Hitec RCD USA, Inc. | 9320 Hazard Way, Suite D, San Diego, CA 92123 | (858) 748-6948 | www.hitecrcd.com

CONTINUES...

Hot on the heels of our wildly popular RDX1 Mini, Hitec is expanding your charging game with the new RDX2. This Mighty Mini features dual independent circuits to charge two batteries simultaneously, regardless of chemistry or capacity. The sleek, compact design allows easy front-loading convenience, while its powerful output and readily accessible balancing and XT60 ports make your battery management moreefficient and effortless.

• Dual Independent Charge Ports

• 5-Amp Charging Output

• 100-Watt Maximum Output

• Charges All Battery Chemistries

• Convenient Front-Loading Design

AC BAlAnCe ChArger

Features

efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.

• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char

• 5-Amp Char• 5-Amp Charging Output • 5-Amp Char• 5-Amp Char• 5-Amp Charging Output • 5-Amp Charging Output • 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Charging Output • 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Charging Output • 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Charging Output • 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Char• 5-Amp Charging Output • 5-Amp Char• 5-Amp Char• 5-Amp Char

• 100-Watt Maximum Output• 100-Watt Maximum Outputatt Maximum Outputatt Maximum Outputatt Maximum Outputatt Maximum Outputatt Maximum Outputatt Maximum Output• 100-W• 100-W• 100-Watt Maximum Output• 100-Watt Maximum Outputatt Maximum Output• 100-W• 100-W• 100-Watt Maximum Output• 100-Watt Maximum Outputatt Maximum Outputatt Maximum Outputatt Maximum Output• 100-Watt Maximum Output• 100-W• 100-Watt Maximum Output• 100-Watt Maximum Output• 100-Watt Maximum Output• 100-W• 100-W• 100-W• 100-W• 100-W• 100-W• 100-W

eatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatureseatures

RDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your chargame with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new game with the new RDX2RDX2RDX2RDX2RDX2RDX2RDX2RDX2RDX2RDX2RDX2RDX2RDX2

features dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cirfeatures dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cirfeatures dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cirfeatures dual independent cirfeatures dual independent cirfeatures dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cirfeatures dual independent cirfeatures dual independent cirfeatures dual independent cirfeatures dual independent cirfeatures dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cirfeatures dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cires dual independent cirtwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslytwo batteries simultaneouslyof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacityof chemistry or capacitycompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frconvenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports

convenience, while its powerful output and eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports

make your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management moremake your battery management moremake your battery management mormake your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management moremake your battery management mormake your battery management moremake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mor

• Dual Independent Charge Portsge Ports• Dual Independent Charge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Portsge Portsge Portsge Ports• Dual Independent Charge Portsge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Charge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Portsge Ports• Dual Independent Charge Portsge Portsge Ports• Dual Independent Charge Portsge Portsge Portsge Portsge Portsge Portsge Ports• Dual Independent Charge Portsge Portsge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Portsge Portsge Portsge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Charge Portsge Portsge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Charge Ports• Dual Independent Char• Dual Independent Char• Dual Independent Char• Dual Independent Char

ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output ging Output

Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular Hot on the heels of our wildly popular RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charging RDX1 Mini, Hitec is expanding your charRDX1 Mini, Hitec is expanding your charging

. This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini . This Mighty Mini es dual independent circuits to charge cuits to charcuits to charcuits to chares dual independent circuits to chares dual independent circuits to charcuits to charcuits to chares dual independent circuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to chares dual independent circuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to chares dual independent circuits to charcuits to charge cuits to charge cuits to charge cuits to charcuits to charcuits to charcuits to charcuits to charge cuits to charge cuits to charge cuits to chares dual independent circuits to charcuits to charcuits to charcuits to charcuits to charcuits to charcuits to chares dual independent circuits to char

egardless dless egardless dless dless dless dless dless dless , regardless egardless egardless egaregardless egardless egaregaregardless egardless egardless egaregaregaregartwo batteries simultaneously, regartwo batteries simultaneously, regartwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, regar, regar, regartwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, r dless egardless egardless egardless egardless egardless egardless dless two batteries simultaneously, regaregartwo batteries simultaneously, regaregar, regaregar, regar, regartwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, regardless egaregartwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, rtwo batteries simultaneously, r, regar, regartwo batteries simultaneously, regardless two batteries simultaneously, regartwo batteries simultaneously, rtwo batteries simultaneously, regardless egardless dless dless dless dless dless egardless . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek, . The sleek,

ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading ont-loading ont-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading compact design allows easy frcompact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading ont-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy front-loading compact design allows easy front-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy front-loading compact design allows easy front-loading ont-loading compact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading ont-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy front-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading ont-loading compact design allows easy frcompact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy frcompact design allows easy front-loading compact design allows easy frcompact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading ont-loading compact design allows easy front-loading compact design allows easy front-loading compact design allows easy front-loading ont-loading ont-loading ont-loading compact design allows easy front-loading compact design allows easy frcompact design allows easy front-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading ont-loading compact design allows easy frconvenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and convenience, while its powerful output and eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports eadily accessible balancing and XT60 ports

make your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management mormake your battery management morefficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.efficient and effortless.

FFFFFFFFFFFFFFFFFFeatureseatureseatureseatureseatureseatureseatureseatureseatureseatures

THE MIGHT

SERVO Issue-1.2020 3

Subscription InformationSERVO Magazine — 2279 Eagle Glen Parkway #112-481

Corona, CA 92883 • (951) 371-8497Call (800) 783-4624 or go to www.servomagazine.com

Subscribe • Gift • Renewal • Change of Info

Issue-1.2020VOLUME 18

06 Mind/Iron An Analog Artifact Worthy of Your Robotics Toolkit

26 New Products

37 The GearBox

72 Advertiser’s Index

73 SERVO Webstore

Departments

For more details on subscribing, see our ad on Page 74.

Combat Zone28 Building a Better Box

30 Stepping Stones —

The Story of Thunder

Child

33 Bringing About the

ApocalypsePage 30

SERVO Magazine (ISSN 1546-0592/CDN Pub Agree#40702530) Issue-1 (Jan-Feb) is published 6X a year for $26.95 per year by T & L Publications, Inc., 2279 Eagle Glen Parkway, #112-481, Corona, CA 92883. Periodicals postage PAID at Corona, CA and at additional entry mailing offices. POST MASTER: Send address changes to SERVO Magazine, 2279 Eagle Glen Parkway #112-481, Corona, CA 92883 or Station A, P.O. Box 54, Windsor ON N9A 6J5; cpcreturns@servomagazine.com.

• Armed and Dangerous?

• HAMR-Jr Time

• Slow as a SlothBot

• Healthcare Gone to the Dogs

• Cheetahs Never Prosper

• Bot or Not?

• Do the Worm

• Draganfly Drones Do Monitoring

• Follow the Bouncing Ball

• Gonna Burst Your Bubble

20 Bots in Brief

4 SERVO Issue-1.2020

07 Grant Imahara Eulogyby David Calkins

10 Experimenting with Walking Robots — Walking Up and Down Hillsby John Blankenship

This series of articles has explored many aspects of

walking robots from the unexpected side effects of various

movements to the need for sensors and how to utilize them.

This final installment utilizes many of the principles discussed

to create a robot that can navigate inclines as easily as level

terrain.

16 Goal Prediction Using AIby Rajat Keshri

Learn the basics of machine learning and the power of

what machine learning can do. This article teaches the

implementation of different machine learning algorithms for

predicting a simple binary classification. It’s mainly focused

on beginners who are very new to machine learning. As an

application to apply what you learn, you’ll discover how to

use different algorithms on predicting if a goal has been

scored or not.

38 Build Your Own Computer-Controlled Three-Axis Robotic Armby Sam DiPietro, Brett Sawka, and Rohan Shah

Having a passion for art but no artistic skill, three

engineering students built a contour image plotter known

as “Bot Ross.” This article explains the design of Bot Ross’s

hardware and software as well as its intended operation.

46 Building a Linear Actuatorby Theron Wierenga

While doing some thinking about building a walking bird

robot, I researched purchasing linear actuators. What I

found is that linear actuators are fairly expensive — especially

if you’re an amateur robot builder with a limited budget.

This led me to thinking about what it would take to build my

own linear actuators.

54 Versatile Stepper Controlby William Cooke

Stepper motors are a staple of robotics. They’re great for

precise speed and positioning. It’s also easy to control one.

But what about two, or three? With different step rates?

For different amounts of time? While your microcontroller

continues doing other tasks? It can quickly become

difficult, but with the technique presented here you can

do all that and use only about two or three percent of the

microcontroller’s time.

61 Laser Alignment System for Your CNC Routerby Roger D. Secura

In this article, I’ll show you how to build a laser power

supply circuit and a special bracket for your CNC router

motor so that you’ll be able to consistently find the edges of

your workpiece. You’re going to like the fact that the power

supply circuit we’ll make only requires three components:

the LM317T voltage regulator and two resistors.

66 Alpha-Writer: A Computer-Controlled Letter Writing Robotic Armby V S Rajashekhar

In this DIY project, I’ll show you how to make a simple

computer-controlled letter writing robot from scratch. It

has two revolute joints connecting two links and at the

end of the robot, there’s an end effector with a pen.

By pressing a button on a screen, you can tell the robot

which letter to do next. It can write all 26 letters of the

alphabet.

70 Appetizer: Connected Cars — A Fast Brewing World in Automotiveby Abhinav Kumar

There’s a huge ecosystem of connected car services and

mobility services startups, technology giants, consulting

companies, and finally, automotive OEMs that are

working tirelessly to modernize the way we commute.

Page 46

Page 54

SERVO Issue-1.2020 5

At my first real job with a communications company, every technician was equipped

with a piece of state-of-the-art test gear designed to function in the harshest environments and with literally constant abuse. Of course, I’m talking about the Simpson 260, easily the most popular analog VOM (volt-ohm meter) of all time.

The best technicians and engineers wouldn’t consider anything else to assist them in diagnosing and maintaining microwave communications gear. I remember the best of the engineers could read a dozen values in only a few seconds. They could accurately estimate values long before the Simpson’s needle moved into final position, simply based on the initial velocity of the needle.

I, on the other hand, lusted after one of the new digital meters on the market. After all, why settle for a reading of only 2-3% full scale accuracy, when a DMM could theoretically take a reading with double the accuracy and to several digits and with a much higher input impedance?

Putting aside the issues of settling time, need for frequent calibration, and the need to be near a 110V outlet, when digital meters first hit the market, they were cool. They were like having one of the first iPhones to hit the street.

Over the years, I worked through several generations of DMMs, ranging from $10 to over $800. I even considered the digital Simpson — a short-lived abomination. My current toolkit includes a portable Fluke 87

PUBLISHED BY

T & L Publications, Inc.

CONTACT

2279 Eagle Glen Pkwy #112-481

Corona, CA 92883

OFFICE: (951) 371-8497

FAX: (951) 371-3052

www.servomagazine.com

SUBSCRIPTION INQUIRIES/

WEBSTORE ORDERS

TOLL FREE: (800) 783-4624

subscribe@servomagazine.com

store.nutsvolts.com

PUBLISHER

Larry Lemieux

publisher@servomagazine.com

ASSOCIATE PUBLISHER/

ADVERTISING SALES

Robin Lemieux

robin@servomagazine.com

EXECUTIVE DIRECTOR/

PRODUCTION

Sean Lemieux

sean@servomagazine.com

EDITOR

Bryan Bergeron

techedit-servo@yahoo.com

CONTRIBUTING EDITORS

Kevin Berry John Blankenship

William Cook V S Rajashekhar

Roger Secura Rohan Shah

Sam DiPietro Brett Sawka

Rajat Keshri Abhinav Kumar

Theron Wierenga Ryan Clingman

Nate Franklin David Calkins

WEBSTORE MARKETING/

COVER GRAPHICS

Brian Kirkpatrick

brian@servomagazine.com

Copyright © 2020 by T & L Publications, Inc.

All Rights ReservedAll advertising is subject to publisher’s approval.

We are not responsible for mistakes, misprints,

or typographical errors. SERVO Magazine

assumes no responsibility for the availability

or condition of advertised items or for the

honesty of the advertiser. The publisher makes

no claims for the legality of any item advertised

in SERVO. This is the sole responsibility of the

advertiser. Advertisers and their agencies agree

to indemnify and protect the publisher from

any and all claims, action, or expense arising

from advertising placed in SERVO. Please send all

editorial correspondence, UPS, overnight mail,

and artwork to: 2279 Eagle Glen Pkwy #112-

481, Corona, CA 92883.

An Analog Artifact Worthy of Your Robotics Toolkit

Mind / Ironby Bryan Bergeron, Editor

6 SERVO Issue-1.2020

DMM and a benchtop Fluke 45 DMM.Other than changing batteries and

leads, these DMMs have been trouble-free and a cornerstone of my repair work. So, why did I add a Simpson 260 to my arsenal, especially when — on specifi cations alone — a DMM with similar capabilities can be had for 5% of the price of a used Simpson 260?

I have to admit the reason is partly nostalgia. After all, handling the 3 lb over-sized Bakelite case and the solid “click-click” rotary switch is pure pleasure. Instead of a series of cold LED or LCD numbers, my measurements are based on a crisp black needle defl ected across a colorful mirrored background.

My reason for acquiring the Simpson 260 (Simpson 260 8p, used, with leather case, $175, eBay) is also partly practical. Measuring the voltage across and current through motors and other actuators is simply easier with an analog meter. The analog meter movement is relatively immune to higher frequency noise and spurious signals, making measurements a lot easier.

In fact, I’ve found the Simpson performs well in just about every task previously covered by my Fluke DMMs. If I could talk with the Simpson designers, the only change I’d suggest is to supplement the current DCV full scale ranges of 2.5V, 10V, 25V, 50V, 250V, 500V, and 1000V with 3.5V and 5.0V or 6.0V. Even so, the 10V full scale range is suffi cient for both 5V and 3.3V circuits.

If you’re convinced that an analog artifact is in your future, the cost of entry is between $50 and $200 used, depending on model and condition, and $350 new (Simpson 260-8p, Amazon).

A point to consider is that, unlike your digital meters and lesser analog VOMs, even an older Simpson is likely to outlast you. SV

Whenever we talk about the famous, we call them “stars.”

The dots of light in an otherwise black sky. However, stars

aren’t the only things in the night sky. About once in our

lifetime, we get to see something even bigger and more

memorable — we are graced with a comet.

A comet isn’t just one point of light in the sky. It fl ies across the

stars leaving a giant trail of lights. That was Grant. It wasn’t enough

that he should be a dot in the sky. Everywhere he went, he made

sure that there was a streak of countless glowing points following in

his wake. Comets are rare and bring with them wonder and magic.

You know they’re special the second you see them.

I fi rst met Grant in 2000, and I knew he was special. We were

just chatting about the nascent fi eld of robots, and he listened to

everything I had to say. He was one of the few people I’ve ever met

that really cared about your opinions. He wasn’t just waiting for his

turn to talk. He wanted to learn from you, about you, and what you

could share with him.

When he did talk, it was invariably about ideas or other people.

Never himself. We bonded over a similar upbringing by single moms

without a strong male infl uence. Which is an all too common thing.

But Grant didn’t just discuss it casually. He was immensely grateful

to his mother for her hard work in raising him, and he was forever

talking her up. How many people actually talk about their moms and

how important they are?

He was already living the dream, working at ILM and in the

incredibly unique position to play both R2-D2 and C-3PO. When The

Phantom Menace went into production, he not only got to build and

Grant Masaru ImaharaOctober 23, 1970 – July 13, 2020

by David Calkins

SERVO Issue-1.2020 7

drive R2, but he frequently put the C-3PO suit on for

public appearances.

He taught me a lot about transparency in those

days. When he drove R2, he’d keep the R/C behind his

hip and drove blind. Not to show off his crazy driving

skills (man, could he drive). No. Just the opposite:

to hide them. He’d subtly cling to a back wall so

that people (especially kids) would only see R2. He

completed the illusion with wonder and amazement.

He didn’t want the accolades. He wanted to make

people happy. To help them believe the magic. To

make them shine. And so, a few more points of light

were born, and trailed him in the sky.

A few years later, he joined Mythbusters. Rather

than shirking the “geek” label, he reveled in it, giving

all of us other geeks a path to follow — unashamed

of any labels that people might put on us. He helped

drive the societal shift to embracing the inner geek in

us all.

While most people might be happy to shine as

a popular TV star, Grant didn’t grow distant. He

continued to help every chance he could with anyone

and everyone in the community. For several years, he

mentored a high school robotics team, long after most

others who had achieved fame would have pulled

away. No matter how tired he was from TV shoots

or how many times he had to cross the Bay Bridge

in a day, he made time for those kids, even donating

considerable money to ensure that they could glow in

the night sky as brightly as he did. And so, even more

points of light appeared in the sky behind him.

As his fame grew, so did his generosity. When old

friends from ILM needed his help on small independent

projects, he was there for them. Not for the money,

but because he could help them. His kindness and

cheerfulness were ever present. Working alongside

him late at night at FonCo on various projects, he was

always the one who was the most sparkling of us, no

matter how late at night (or early in the morning). We

all shone a bit brighter when we were around him ...

and more lights followed him in the sky.

No matter what time it was, Grant the comet just

glowed. His smile and optimism were contagious, and

he stood out in a crowd even if you had no idea who

8 SERVO Issue-1.2020

he was. He cracked jokes, slapped you on the back, and

saw the good in everyone and everything. He wasn’t

good to others to keep up his image. He was kind and

generous to everyone because that was the only way

he knew how to be. When he helped you, you always

knew everything was going to be just fi ne when you

saw him nod and arch his brow.

I had the great fortune of being a close enough

friend to go out socially with Grant. One night at

dinner, as we discussed solemn non-roboty things, a

little girl approached the table. Grant never hesitated

and went from being dulled by the discussion’s clouds

to glowing and listening to everything she had to say. I

don’t think it ever occurred to him to shoo her away ...

and one more light in the sky was born.

On several occasions, when we geeks would

go out “marauding” (as he called it), he was often

approached by fans for photos. He never turned

anyone down and didn’t just take the photo. Grant

made sure to thank them for their fandom. To ask

them about their lives. And to truly listen to them as

they shared their hopes and dreams with him (on more

than one occasion, the fans got more of him than we

did).

At the height of Mythbusters, he called me out of

the blue to go to dinner. It wasn’t just a casual dinner

between old friends, but he looked gravely at me and

said, “You know, now that I’ve made it, I want to help

everyone. What can I do to help RoboGames?”

This was typical Grant. He could have bought a

bunch of fancy cars and hidden away in a condo on a

beach somewhere, but he never forgot where he came

from. So, he MC’d a bunch of events to help everyone.

(You can watch one of them at https://youtu.be/

a45qx2bV6JQ. The fi rst 1:26 of him and Kiki is great.

You can see his passion and honest excitement. Grant

doesn’t appear for the remainder of the clip.)

He didn’t just help host. He roamed the pits and

made contestants from around the world feel special.

He wasn’t basking in his fame. He was a kid in a toy

shop. He just knew that he could make things better

(even helping teams fi x their robots). And, while

helping everyone else, he always made sure that he

took care of his mom (which is far more than most of

us can say ...).

While a lot of stars might turn to product

endorsement, Grant only ever used his name to help

others (other than the McDonalds thingy ... but most

people have forgotten that). He was always teaching

and sharing to help people. If you saw his comet

streaking across the sky, it was telling you how to

make cool stuff and always focused on education.

Time is always more precious than money, and

Grant was most generous with his time. Even with all

the demands of work and travel, he always found time

for others. When a close friend was having a Sailor

Moon themed wedding, he spent months making a

movie-worthy perfect giant Cutie Moon Rod which lit

up for the bride.

Even his personal robotics projects weren’t to be

kept in his living room. He made a replica BB-8 and

a Baby Yoda not so much for himself, but for kids in

hospitals who needed something to cheer them up.

How many people who could do that, would?

The trail he left — as all comets do — can be seen

more for the countless points of light trailing it, rather

than the single star at the front. There are hundreds

of stories of Grant’s generosity, just like the sparkling

dots of light left in a comet’s wake. He was rare and

unique, fi tting seamlessly into whatever group of

people he encountered. But like a comet, his presence

in the sky was all too short, but never to be forgotten.

He stood apart in a fi eld of endless stars, and it’s his

light that will be remembered.

You’re lucky if you get to see a comet once in your

lifetime. Grant was that comet.

When you look up to the sky and you see a comet

streaking across it followed by an uncountable number

of twinkling lights, look to see if it has that sly smile

and an arched brow.

Thanks Buddy.

SERVO Issue-1.2020 9

10 SERVO Issue-1.2020

Most walking robots built by hobbyists walk by

transitioning between various static poses; an

approach that — while relatively easy — has many

limitations. In addition, affordable walking robots are

typically powered by inexpensive servo motors which have

limited torque for small movements, imprecise repeatability,

and signifi cant play in their gear trains. A major goal of my

experimentation with walking robots was to determine ways

of dealing with these limitations.

The experimentation also revealed that two walking

robots can be far different from each other when compared

with two wheel based robots. This simply means that

techniques that work for one walker might be more or less

successful with another, due to differences in the two robots

such as the center of gravity, the number of joints, and the

quality of the motors and sensors used.

Perhaps the most important revelation is that building

a walking robot with hobby-level hardware is extremely

diffi cult; certainly far more diffi cult than I expected. On the

positive side, walkers provide a very different experience for

hobbyists and when something fi nally works, the process

can be very rewarding.

This fi nal article of the series demonstrates how

applying some of the principles discovered during

experimentation gave my robot the capability to walk on a

sloped terrain as well as a fl at surface.

A Basic Principle

A basic principle of my walking process is to always

know where the major joints are currently located, so that

it’s easy to move to the next position. To that end, my

software always moves major joints in fi xed increments. Let’s

look at an example.

Suppose we want the robot to take a step of size “D.”

It might start by lifting the leg, then extending it. Lifting

This series of articles has explored many aspects of walking robots from the unexpected side effects of various movements to the need for sensors and how to utilize them. This final installment utilizes many of the principles discussed to create a robot that can navigate inclines as easily as level terrain.

Experimenting with Walking

Robots ♦ Part 5

Walking Up and Down Hills

SERVO Issue-1.2020 11

the leg could be accomplished by moving the thigh

forward D degrees and the knee backward by the same

amount. Note that this would move the leg slightly

forward while keeping the foot parallel with the fl oor as

shown in the left side of Figure 1.

After a short delay, we could extend the calf

portion of the leg forward (again by D degrees), but in

order to keep the foot parallel with the fl oor, we also

need to tilt the ankle forward by D degrees. Always

moving the joints in increments of D degrees makes it

easy to keep track of their current location.

The problem is that sometimes when you move a

robot’s leg, it might not appear to be in the position

you intended. If the weight of the raised leg, for

example, causes the robot to lean forward due to stress

on the motors and gear train in the supporting leg,

then the extended foot would certainly not be parallel

with the ground (see the right side of Figure 1).

The left side of Figure 1 looks the way we want

the robot to look after the leg is raised, but the

right side is probably how it will actually be with most

servomotors. Often, people programming a walking robot

like this will try to adjust the amount the joints are moved to

make the robot look like the left side.

Unfortunately, if the stress is relieved from the

supporting leg (perhaps by the next movement which

changes the robot’s balance), the robot’s new position will

be far different than what you’re trying to accomplish. If you

try to keep the robot posed as expected (rather than always

using fi xed movements), then fi guring out how to move to

new positions (that might have different balance issues) can

quickly become an unmanageable task.

The best solution is to try to keep the robot balanced,

but ultimately, you should simply accept that the robot may

not always appear exactly as expected. If you assume the

robot’s joints are where they’re supposed to be (no matter

how they look) and move them accordingly, the robot —

over time — will generally end up reasonably close to where

you expect.

The Code

Figure 2 shows the top levels of my walking code

application. The fi rst sub-routine called in this code is

FindBalance, which was discussed in Part 4 of this series. It

causes the robot to autonomously maintain its balance as

the board the robot is standing on is tilted to create an up

or down slope. An important aspect of this routine is that it

returns the slope of the fl oor (see Part 4 for more details).

The code in Figure 2 also establishes some global

variables (names that begin with underscore are global

in RobotBASIC) that will be used to control the walking

routines. Using global variables allows them to be accessed

from within RobotBASIC’s sub-routines which utilize local

variables. This minimizes the need to pass parameters that

are needed by many routines.

Once we know the slope of the fl oor, it can be used to

alter the step size (this is basically the D value mentioned

earlier). In general, adding the slope of the fl oor to the

primary step size will cause the robot to step higher when

it’s moving up an incline and step lower when it’s going

downhill. Various parameters such as the lean angle are also

set in this routine. The lean angle is how much the robot

should lean in order to lift the opposing foot from the fl oor.

You could arrive at parameters like this experimentally or

even have the robot do it autonomously by leaning until the

foot switches indicate the foot is off the fl oor.

A variable DeltaXtilt is also created that indicates how

much the accelerometer readings will change when the

robot leans to one side to take a step. The number is just

an approximation, but it works well. We’ll see how these

parameters are used shortly.

The fi nal action before beginning the walk is that the

robot will lean its body forward slightly if it’s going up a

slope and backward if it’s going down. This is not required,

but it does help the robot maintain its balance.

The Walk routine uses a loop to make right and left

steps. Before the loop, a call to StartWalk leans the robot to

the left (based on the variable _LeanAngle). When the fi nal

step is taken, StopWalk leans the robot to the right to return

the robot to its normal standing position.

By John Blankenship

Experimenting with Walking

Part 5

FIGURE 1.

To post comments on this article and fi nd any associated fi les and/or downloads, go to

www.servomagazine.com/magazine/issue/2020/01.

12 SERVO Issue-1.2020

Taking Steps

The difficult work is performed by the routine TakeStep

which can perform either a right or left step. In either

case, TakeStep assumes that the robot is already leaning

appropriately, so that the stepping foot is off the ground.

The routine ends with the robot leaning in the opposite

direction, so it’s

prepared for the

next step. The actual

step is accomplished

by calling four

routines as shown

in Figure 3. These

four routines will

move the stepping

leg forward, bring

the body forward

over the stepping

foot, lean the robot

back to the center

to regain a good

balance, and finally

sub LegForward(leg)

amount = _StepSize

gosub InitServoNames

call FromCurServoPos(leg+1,amount)

delay 300

call FromCurServoPos(leg+3,5) // raise toe slightly to prevent stubbing

call FromCurServoPos(leg+2,-amount)

if leg = RGT

call BalanceWithArms(100-_DeltaXtilt,_DesiredYtilt)

else

call BalanceWithArms(100+_DeltaXtilt,_DesiredYtilt)

endif

delay 500

call FromCurServoPos(leg+2,amount)

call FromCurServoPos(leg+3,-amount-5) // lowers toe

call BalanceWithArms(100,_DesiredYtilt)

return

Application:

gosub InitApplication

delay 500

// local variables to control walking

_DesiredXtilt = 100 // used for balance with arms

_DesiredYtilt = 100

_LeanAngle = 12

_PrimaryStepSize = 25

call FindBalance(CurSlope)

_CurrentSlope=CurSlope

_StepSize = _PrimaryStepSize+_CurrentSlope // Step higher going up hills (lower/down)

_DesiredYtilt+=_CurrentSlope

_DeltaXtilt = _LeanAngle/5

// adjust body for hill walking

call FromCurServoPos(Rthigh,_CurrentSlope) // lean back going down slope

call FromCurServoPos(Lthigh,_CurrentSlope) // and forward going up

delay 500

call Walk(4) // 4 steps

return

sub Walk(Num)

gosub InitServoNames

gosub StartWalk

delay 1000

stepping _MODE

for i=1 to Num

call TakeStep(RGT)

call TakeStep(LFT)

next

gosub StopWalk

return

FIGURE 4.

sub TakeStep(leg)

call LegForward(leg)

call BodyForwardOverFoot(leg)

call LeanToCenter(leg)

call StartOpStepPosition(leg)

return

FIGURE 3.

FIGURE 2.

SERVO Issue-1.2020 13

lean further so the robot is ready to step

with the opposite leg.

Moving the Leg Forward

The routine LegForward is shown in

Figure 4. It uses the leg value passed to

it to access the different joints (+1 is the

thigh, +2 is the knee, and +3 is the F/R

ankle). In keeping with the philosophy

discussed earlier, all joints are moved

based on the current step size.

Notice also that the toe is raised

slightly at one point to help prevent

it from stubbing (in case the robot is

leaning forward as depicted by Figure

1), and then lowered again at the end

of the routine. Notice also that the final

line in this routine moves the arms to

improve the robot’s balance.

Executing this routine puts the

robot in the position shown in Figure

5. Notice the knee and ankle joints are

now in a straight line, extending the

foot forward.

Moving the Body Forward

The routine in Figure 6 moves the

robot’s body over the stepping leg.

Because the robot is balanced on one

foot while this is happening, the step-

sized movements are divided into smaller

actions and performed within a loop.

The use of RobotBASIC’s modulo

operator (#) and integer divide ensures

that each movement is fully completed.

Notice that the arms are used to help

maintain balance as the movement

progresses.

Figure 7 shows how the robot will

appear after this routine is executed. This

pose looks very much like Figure 5, but

the body is definitely forward. Compare

the knee and ankle joints in Figures 5

and 7. The camera angle makes these

differences very easy to see.

Leaning Back to Center

At this point in the sequence, the

sub BodyForwardOverFoot(leg)

gosub InitServoNames

SS = _StepSize

if leg=RGT

call FromCurServoPos(Rknee,-SS#4)

call FromCurServoPos(Rankle,SS#4)

call FromCurServoPos(Lthigh,-SS#4)

call FromCurServoPos(Lknee,SS#4)

for i=1 to 4

call FromCurServoPos(Rknee,-SS/4)

call FromCurServoPos(Rankle,SS/4)

call FromCurServoPos(Lthigh,-SS/4)

call FromCurServoPos(Lknee,SS/4)

call BalanceWithArms(100-_DeltaXtilt,_DesiredYtilt)

next

elseif leg=LFT

call FromCurServoPos(Lknee,-SS#4)

call FromCurServoPos(Lankle,SS#4)

call FromCurServoPos(Rthigh,-SS#4)

call FromCurServoPos(Rknee,SS#4)

for i=1 to 4

call FromCurServoPos(Lknee,-SS/4)

call FromCurServoPos(Lankle,SS/4)

call FromCurServoPos(Rthigh,-SS/4)

call FromCurServoPos(Rknee,SS/4)

call BalanceWithArms(100+_DeltaXtilt,_DesiredYtilt)

next

call

endif

return

FIGURE 5.

FIGURE 6.

FIGURE 7.

14 SERVO Issue-1.2020

robot is still leaning to one side, so it needs to move its

weight back toward the stepping foot. Figure 8 shows how

this is accomplished.

Basically, it shortens the leg the robot is currently

standing on in order to lower the stepping foot to the

ground. You might think the amount of this lowering would

change if the robot is moving on an incline. The reason it

doesn’t is because we have the robot taking a bigger (thus

higher) step when it’s walking up an incline and a smaller

(lower) step when it’s going downward.

This adjustment to the step size means the stepping

foot will be approximately the same distance from the floor

regardless of the terrain’s slope. This means we can always

lower the robot a proper amount by moving the joints in

the supporting leg by the _PrimaryStepSize initialized earlier

(this is the step size for level terrain). Figure 9 shows how

the robot will be positioned after this routine is executed.

Notice the robot is

well balanced, but

the stepping foot

is forward in the

stance.

The action

of lowering the

stepping leg to the

ground is much

different than

letting the robot’s

weight pull the

body forward onto

that leg.

This action

helps the robot

maintain its

balance and is a

vital move when

walking up and

down inclines.

sub StartOpStepPosition(leg)

gosub InitServoNames

if leg=RGT

OpLeg = LFT

else

OpLeg = RGT

endif

call Lean(leg,_LeanAngle/2)

call FromCtrServoPos(leg+2,0) // 0 forces startup angles

call FromCtrServoPos(leg+1,-_CurrentSlope) // maintains body tilt for

call FromCtrServoPos(OpLeg+1,-_CurrentSlope) // navigating a slope

call FromCtrServoPos(OpLeg+2,0)

call FromCtrServoPos(OpLeg+3,0)

call Lean(leg,_LeanAngle/2)

// balance based on current lean direction

if leg = LFT

call BalanceWithArms(100-_DeltaXtilt,_DesiredYtilt)

else

call BalanceWithArms(100+_DeltaXtilt,_DesiredYtilt)

endif

delay 500

return

sub LeanToCenter(leg)

gosub InitServoNames

if leg=RGT

OpLeg = LFT

else

OpLeg = RGT

endif

call ShortenLegForStep(OpLeg,_PrimaryStepSize#4)

delay 100

call Lean(leg,_LeanAngle#4)

call BalanceWithArms(_DesiredXtilt,_DesiredYtilt)

for i=1 to 4

call ShortenLegForStep(OpLeg,_PrimaryStepSize/4)

delay 100

call Lean(leg,_LeanAngle/4)

call BalanceWithArms(_DesiredXtilt,_DesiredYtilt)

next

delay 300

return

FIGURE 10.

FIGURE 8.

FIGURE 9.

SERVO Issue-1.2020 15

Preparing to Step with the Opposite Leg

With the robot balanced on

two feet again, the next action is

for the robot to lean away from

the leg that will make the next

step. Figure 10 shows how this is

accomplished.

In this routine, all the joints

are reset to their original balanced

position (as was established by

StartWalk, except that the robot

may be leaning either left or

right depending on which foot

is stepping). This always leaves

the robot ready to proceed with

the next step or to return to the

normal standing position.

Figure 11 shows how the

robot is positioned after this

routine is executed.

Conclusion

Programming hobby-

oriented walking robots can be

both frustrating and rewarding.

Experimenting with a variety of

movements can greatly improve

your understanding of the

problems and ultimately help you

find innovative solutions. Here’s a

YouTube video demonstrating my

robot in action: https://youtu.

be/LB_uBJh5bQ8.

Watching it actively balance

as it walks on different slopes

should be exciting for anyone who

understands how difficult this

project is. I’m sure that fine-tuning

properties such as delays, motor

speeds, and balancing algorithms

could greatly improve the robot’s

performance, but at least for now,

such modifications will be left for

the motivated reader. SV

FIGURE 11.

16 SERVO Issue-1.202016

Goal Prediction Using AI

From this article, you’ll discover the basics of machine learning and the

power of what machine learning can do. I’ll discuss the implementation

of different machine learning algorithms for predicting a simple binary

classifi cation. This article is mainly focused on beginners who are very

new to machine learning. I’ll show you how to use different algorithms

on predicting if a goal has been scored or not by Cristiano Ronaldo — the

famous Portuguese professional footballer who plays as a forward for

Serie A club Juventus and captains the Portugal national team. He is often

considered the best player in the world and widely regarded as one of the

greatest players of all time.

SERVO Issue-1.2020 17

IntroductionWhile watching any football (soccer) match, we want

the team that we support to score a goal. We wait patiently

until a player from our team gets close enough to the goal

and makes a shot ... which seems to be going into the goal

but misses, sadly. Can AI (Artificial Intelligence) predict and

explain why that player missed the shot from that particular

location using data analytics and machine learning?

In this article, we’ll experiment with different ML

(machine learning) algorithms and teach an AI to predict if a

player will score a goal or not.

Machine learning plays a key role in many different

applications such as computer vision, data mining, natural

language processing, speech recognition, and others. ML

provides potential solutions in all the above-mentioned

domains and more. It’s surely going to be a driving force in

our future digital civilization.

Here, we’ll see how we can use different machine

learning algorithms and build a simple binary classifier which

will classify whether a goal can be scored or not, based on

the given input data. This project was done as part of a

hackathon I participated in and from which the dataset was

provided.

In the following section, we’ll go over some basic theory

of different machine learning algorithms which we’ll be

trying to code and apply in the later part of this article.

Some TheoryThere are many machine learning algorithms present.

In this project, we’ll be using classification algorithms since

we’ll be needing to predict whether a goal is scored or not.

This is also called binary classification.

If you have basic knowledge of different machine

learning algorithms and types of classification in machine

learning, feel free to skip the theory section.

Classification in machine learning is done in two ways:

supervised and unsupervised. Supervised learning involves

the data set given with the output each data point should

produce. The algorithm learns the patterns which produce a

certain output and tries to generalize it with supervision.

Supervised learning basically contains the output

labels to be predicted in the data set, and learns how to

predict those values by backtracking and generalization.

Unsupervised learning trains on the data and tries to

generalize blindly without knowing what category each data

point belongs to. It creates a pattern and generalizes the

data points based on its features, and creates output labels

for them during the training process.

Here, we’ll be focusing only on the supervised

learning method. Some of these methods which we’ll be

experimenting with are linear regression, logistic regression,

random forest, and neural networks.

To understand how these algorithms work, check the

following links which offer great explanations and can help

you to understand the workings of these algorithms:

1. Linear Regression: https://towardsdatascience.com/

linear-regression-detailed-view-ea73175f6e86

2. Logistic Regression: https://towardsdatascience.com/

logistic-regression-detailed-overview-46c4da4303bc

3. Random Forest: https://towardsdatascience.com/

random-forest-and-its-implementation-71824ced454f

4. Neural Networks: https://towardsdatascience.com/

first-neural-network-for-beginners-explained-with-

code-4cfd37e06eaf

Let’s start with understanding the inner workings and

the approach for our project of predicting if goals are scored

or not. Before we start with any of the code, the first thing

we should do is to go through the data set thoroughly.

We must understand the data set completely and try

to figure out the most important features from the data

set which we’ll be using for training our model. Sampling

and extracting wrong features might sometimes lead to

inaccuracies in your model.

PrerequisitesThe following packages will be used in the development

of this project. Also, we’ll be using Python 3.6 here, but any

version above 3.6 should be fine to use.

1. Sklearn: Machine learning library.

2. Pandas: Library used for importing the csv files and

parsing the columns.

3. Numpy: Library used for storing the training data in an

array. Numpy arrays are most widely used to store the

training data and the sklearn library accepts the input

data in the form of numpy arrays.

4. If any of the libraries are not present in your system,

just pip install that particular library. The guide to use

pip is at https://www.w3schools.com/python/

python_pip.asp.

The following shows the code snippet with all the

libraries to be imported:

import pandas as pdimport numpy as npimport mathimport scipyfrom sklearn.preprocessing import LabelEncoder, OneHotEncoderfrom sklearn.model_selection import train_test_splitfrom sklearn.linear_model import LinearRegressionfrom sklearn.model_selection import train_test_splitfrom sklearn.datasets import load_boston

To post comments on this article and find any associated files and/or

downloads, go to www.servomagazine.com/magazine/issue/2020/01.By Rajat Keshri

18 SERVO Issue-1.2020

from sklearn.metrics import mean_squared_errorfrom scipy.stats import spearmanrfrom sklearn.ensemble import RandomForestClassifierfrom sklearn.preprocessing import scalefrom sklearn.linear_model import LogisticRegressionfrom sklearn.model_selection import train_test_splitfrom sklearn import preprocessingfrom sklearn import svmfrom sklearn.ensemble import RandomForestClassifierfrom sklearn.neural_network import MLPClassifier

Dataset PreprocessingThe data set used here is a csv file with information

about different matches played by Real Madrid against

different teams. The data set contains different fields

describing the goal scored by Ronaldo at different situations

and scenarios, like what time was the goal scored, how

much distance from the goal, what was the shot power,

what angle did he score at, etc. As mentioned before, this

data set was given to me during a hackathon, so I’m not

sure if it’s publicly available on Kaggle or any other website.

Either way, the data set is included in the article downloads

or you can get it from https://github.com/rajatkeshri/ZS-

HACK-predict-ronaldo-goal.

Figure 1 shows some of the columns for the data set.

From the data set, we’ll be using the following columns as

input data: location_x, location_y, power_of_shot, distance_

of_shot, remaining_sec, and is_goal column as the output

label. You can use the other fields for training the model and

experimenting with it, but in this article, I’ll just explain the

use of the input field data columns listed above.

You’ll notice there are many fields which are empty and

there’s a lot of noise in this data set. Our first step is to go

through the data set and fix the noisy data and remove all

the empty fields.

Let’s jump to the code now. First, we open the data set

csv file using pandas and define the columns which act as

the input data and the columns which are the output labels

for training.

Here, column 10 is the “is_goal” column which acts like

the output label and 2,3,4,5,9 columns are the input labels

location_x, location_y, remaining_sec, power_of_shot, and

distance_of_shot, respectively. If you want to try training

your model with other feature columns from the data.csv,

then just add those column numbers in the array.

datasets = pd.read_csv(‘data.csv’)output=pd.DataFrame(datasets)cols = [10]output = output[output.columns[cols]]df = pd.DataFrame(datasets)cols = [2,3,4,5,9]df = df[df.columns[cols]]

Once we have read the features from the csv files,

we must go through and remove all the noise from these

columns. We loop through the features and check if a

particular value for that column if NAN or not. If it’s NAN,

we drop the entire row, removing the entire noisy data.

Once the noisy data is removed, we store the entire 2D

array of multiple column features in variables X and Y:

#Removing rows with Output label not definedk=0x=[]for i in df[“is_goal”]: if math.isnan(i): x.append(k) #print(i) k+=1df=(df.drop(x))#Removing rows with distance of shot not definedk=0x=[]for i in df[“distance_of_shot”]: if math.isnan(i): x.append(df.index[k]) #print(i) k+=1df=(df.drop(x))#Removing rows with power of shot not definedk=0

Figure 1. Dataset in csv format.

SERVO Issue-1.2020 19

x=[]for i in df[“power_of_shot”]: if math.isnan(i): x.append(df.index[k]) #print(i) k+=1df=(df.drop(x))#Removing rows with X axis location not definedk=0x=[]for i in df[“location_x”]: if math.isnan(i): x.append(df.index[k]) #print(i) k+=1df=(df.drop(x))#Removing rows with Y axis location not definedk=0x=[]for i in df[“location_y”]: if math.isnan(i): x.append(df.index[k]) #print(i) k+=1df=(df.drop(x))#print(df)#Removing rows with remaining time not definedk=0x=[]for i in df[“remaining_sec”]: if math.isnan(i): x.append(df.index[k]) #print(i) k+=1df=(df.drop(x))#print(df)X = df.iloc[:, :-1].valuesY = df.iloc[:, 4].values

Now we have our clean data set. The next step is to

split the entire data into train and test data. This is done so

that we train our model on the train data and then test it

for its accuracy and score on the test data. This will help us

understand where our model stands in predictions and can

thus help us in tweaking the model.

To split into train and test data, we use the function

train_test_split which is imported from the sklearn library.

Random state basically means the percentage of data which

will be used as train and test data; 0.2 means 20%:

(X_train, X_test, Y_train, Y_test) = train_test_split(X, Y, random_state=0.2)

TrainingOkay. We’ve finished understanding the data set and

also cleaned it with some pre-processing. The only step left

is training the model. As mentioned earlier, we’ll be training

our model using linear regression, logistic regression,

random forest regression, and neural network. These

algorithms are available within the sklearn library directly

and that is what we’ll be using.

First, we create objects of different machine learning

algorithms and then pass our input features with output

labels to them. These algorithms generalize upon the data

we feed them.

To train these models, we call “.fit” on these objects. For

more information on each of the machine learning algorithm

classes, refer to https://scikit-learn.org/stable.

LR=LinearRegression()Lr=LogisticRegression(random_state=0, solver=’lbfgs’, multi_class=’ovr’)RF = RandomForestClassifier(n_estimators=100, max_depth=2, random_state=0)NN = MLPClassifier(solver=’lbfgs’, alpha=1e-5, hidden_layer_sizes=(5, 2), random_state=1)LR.fit(X_train,Y_train) #linear regressionLr.fit(X_train,Y_train) #logistic regressionRF.fit(X_train, Y_train) #random forestNN.fit(X_train, Y_train) #neural network multi-layer perception model

Once the training is complete, we check how different

models have performed. This can be done by calling the

“.score” method. The .score method prints an accuracy on

how our model performs on the test data:

print(LR.score(X_test,Y_test))print(Lr.score(X_test,Y_test))print(RF.score(X_test,Y_test))print(NN.score(X_test,Y_test))

Also, if we want to check the predictions on our test

data or give new data values and predict whether a goal is

scored or not, we can do it by using the “.predict” method.

The output produced after the predict method is either

1 or 0, where 1 stands for “Yes, he scored a goal!” and 0

stands for “Hard luck, he will definitely score next time.”

loc_x = 10loc_y = 12remaining_time = 20distance = 32power_of_shot = 3custom_input=[[loc_x,loc_y,remaining_time,power_of_shot,distance]]print(LR.predict(X_test))print(Lr.predict(X_test))print(RF.predict(X_test))print(NN.predict(X_test))print(Lr.predict(custom_input))

ResultsFirst of all, congratulations! We have successfully built

a binary classification model AI which predicts whether

Ronaldo can score a goal or not. We observed that it’s a

basic binary classification problem; the logistic regression

performs the best with approximately 95% accuracy, but the

other machine learning models perform and give a score

of approximately 60–70% accuracy. This accuracy can be

increased by adding more features to the training of the

model.

I hope you enjoyed this article. Cheers! SV

The entire project code is included in the article downloads and can also be found at https://github.com/rajatkeshri/ZS-HACK-

predict-ronaldo-goal.

botsIN BRIEF

Researchers at the

Université de Sherbrooke in

Canada developed a waist-

mounted hydraulic arm that

can help you with all kinds

of tasks.

Photos courtesy of

Université de Sherbrooke.

The researchers envision a number of

applications for their supernumerary arm,

including: vegetable picking (a, b); painting a wall

(c); washing a window (d); handing tools to a

worker (e, f); and playing badminton (g).

Armed and Dangerous?

Researchers from Université de Sherbrooke

in Canada have designed a waist-mounted,

remote controlled hydraulic arm that can help

you with all kinds of tasks. Oh, and you can

smash through walls with it too.

This type of wearable robotic arm is

known as “supernumerary.” The system

created by the Canadian researchers (in

partnership with Exonetik) has three

degrees of freedom and is actuated by

magnetorheological clutches and hydrostatic

transmissions with the goal of “mimicking the

performance of a human arm in a multitude

of industrial and domestic applications.” (Like

wall punching.)

The hydraulic system provides

comparatively high power, but the power

system itself is connected to the user through

a tether, minimizing how much mass the user

has to actually wear (and keeping the inertia of the arm low) while also limiting mobility somewhat.

Off-board power does put a bit of a dampener on the superhero potential, but in practical

terms, users aren’t likely to be moving around all that much. If they are, mobile options could include

being tethered to an autonomous vehicle that follows you around or perhaps a more portable

backpack power unit.

The robotic arm itself weighs just over four kilograms — about the same as a real human arm.

It can lift 5 kg and has a maximum end effector speed of 3.4 meters per second, with a workspace

that’s restricted to keep it from smashing you into a wall.

At the moment, there isn’t much in the way of autonomy since the arm is being controlled by a

second human via a miniature handheld arm in a master-slave configuration. The researchers suggest

that adding some sensors could allow the arm to do things like pick vegetables next to the user, as

well as do more collaborative tasks like providing tool assistance.

You can think of it as being able to act as a co-worker, either directly increasing productivity by

performing the same task as the user in parallel, or doing some different tasks in order to free up

the user to do

stuff that requires

creativity or

judgement.

20 SERVO Issue-1.2020

bots IN BRIEF

About the size of a penny, HAMR-Jr is one of the smallest and

fastest insect-scale robots, capable of running at nearly 14 body

lengths (30 centimeters) per second. Photo courtesy of Kaushik

Jayaram/University of Colorado Boulder/Harvard SEAS.

Georgia Tech roboticists

are exploring the idea

of “slowness as a design

paradigm” through an

arboreal robot called

SlothBot.

Photo courtesy of

Georgia Tech.

HAMR-Jr Time

The Harvard Ambulatory MicroRobot

(HAMR) was a bit chunky back in 2018,

measuring about five centimeters long and

weighing around three grams. However, a new

version of HAMR has been introduced. Called

HAMR-Jr, it’s significantly smaller at just a

tenth of the weight and it comes up to about

knee-high on a cockroach.

HAMR-Jr may be tiny, but it’s no slouch.

Piezoelectric actuators can drive it at nearly

14 body lengths (30 cm) per second, at a gait

frequency of 200 Hz. The actuators can be

cranked up even more approaching 300 Hz,

but the robot actually slows down past 200

Hz because it turns out that 200 Hz hits a

sort of resonant sweet spot that gives the

robot as much leg lift and stride length as

possible.

Slow as a SlothBot

We tend to focus on motion a lot with robots,

and the most dynamic robots get the most

attention. This isn’t to say that highly dynamic

robots don’t deserve our attention, but there are

other robotic philosophies that, while perhaps less

visually exciting, are equally valuable under the right

circumstances.

Magnus Egerstedt, a robotics professor at

Georgia Tech, was inspired by some sloths he met

in Costa Rica to explore the idea of “slowness as a

design paradigm” through an arboreal robot called

SlothBot.

Since the robot moves so slowly, why use a

robot at all you ask. It may be very energy-efficient,

but it’s definitely not more energy efficient than a

static sensing system that’s just bolted to a tree for example. The robot moves but it’s also going to be

much more expensive (and likely much less reliable) than a handful of static sensors that could cover

a similar area. The problem with static sensors, though, is that they’re constrained by power availability,

and in environments like under a dense tree canopy, you’re not going to be able to augment their

lifetime with solar panels.

If your goal is a long duration study of a small area (over weeks or months or more), SlothBot

is uniquely useful in this context because it can crawl out from beneath a tree to find some sun to

recharge itself, then crawl right back again to resume collecting data.

SERVO Issue-1.2020 21

Cheetahs Never Prosper

The North Carolina State cheetah robot

— called LEAP, or Leveraging Elastic

instabilities for Amplified Performance — is a

soft robot that can significantly outpace other

soft robots by borrowing inspiration from the

ways real cheetahs flex their spines to achieve

speed and power. By making the soft robot’s

flexible spine able to quickly flex and extend

to mimic the active role of a cheetah’s spine,

it’s possible to quickly propel the soft robot

forward on the ground (and even underwater).

Healthcare Gone to the Dogs

Some coronavirus patients at

Brigham and Women’s Hospital

in Boston are being greeted by a new

kind of nurse: a four-legged robot

named “Spot.”

Boston Dynamics’ famed dog-

like robot has been working with

patients at the hospital to provide a

buffer between potentially contagious

cases and swamped health care

officials.

“It’s kind of fun working with it,”

Dr. Peter Chai recently told Digital

Trends. “[Spot] is not that hard to

control, and it gets us to where we need to be without being exposed.”

The robot — which is best known for a series of viral videos showing its ability to walk, jump,

and even dance on four legs — has been lending a helping hand (leg?), according to authorities at

the hospital and Boston Dynamics.

“Our hope is that these tools can enable developers and roboticists to rapidly deploy robots

in order to reduce risks to medical staff,” Boston Dynamics wrote in a recent blog post announcing

the collaboration.

Chai said Spot is being used in the hospital’s outdoor triage tent for patients who have upper

respiratory symptoms but are not sick enough to stay in the hospital. Spot greets patients with an

iPad-like device that allows them to see and talk to a physician virtually.

Photo courtesy of Jie Yan/North Carolina State University.

22 SERVO Issue-1.2020

Do the Worm

General Electric is getting into giant robot

earthworms.While this might sound unlikely, GE’s

research division has landed a big $2.5 million award

from the Defense Advanced Research Projects Agency

(DARPA) to ensure the project continues crawling

along.

“What makes this so unique is that we’re really

drawing inspiration from two sources in nature: the

earthworm and tree roots,” Deepak Trivedi, who is

leading this project for GE Research, recently told

Digital Trends. “From the earthworm, we’re mimicking

its fast rhythmic movements to rapidly and efficiently

form the tunnels we’re trying to form. And from the

tree roots, we’re mimicking [their] scale and ability to create large force by studying how roots grow into the

ground. It’s the combination of these two forces of nature that makes our project — and robot — so unique.”

The soft robot tunneler is made up of large segmented pieces which act like the fluid-filled “hydrostatic

skeleton” found in invertebrates. The robot’s artificial muscles move like a real earthworm’s in order to

propel it forward, while the segmented design also gives it impressive freedom of movement and the ability to

maneuver into difficult-to-reach places.

Bot or Not?

For the past several years, there’s been heightened

concern about the impact of so-called bots on

platforms like Twitter. A bot in this context is a fake

account synonymous with helping to spread fake news

or misinformation online.

So, how exactly do you tell the difference between

an actual human user and a bot? While clues such as

the use of the basic default “egg” avatar by Twitter,

a username consisting of long strings of numbers,

and a penchant for tweeting about certain topics

might provide a few pointers. However, that’s hardly

conclusive evidence.

That’s the challenge a recent project from a pair of researchers at the University of Southern

California and University of London set out to solve. They have created an AI that’s designed to sort fake

Twitter accounts from the real ones based on their patterns of online behavior.

“Detecting bots can be very challenging as they continuously evolve and become more

sophisticated,” Emilio Ferrara, research assistant professor in the USC Department of Computer Science,

told Digital Trends recently. “Existing tools that work well with older and simpler types of bots are not

as accurate to predict more complex ones. So, it’s always exciting to identify new, previously unknown

characteristics of the behavior of human users that are not yet exhibited by bots. This could [be used to

help] improve the accuracy of detection tools.”

The researchers leveraged various datasets of hand-labeled examples of both fake and real Twitter

account messages produced by other researchers in the community. In total, they trained their system on

8.4 million tweets from 3,500 human accounts and an additional 3.4 million tweets from 5,000 bots. This

helped them to uncover a variety of insights into tweeting patterns.

For instance, human users are up to five times more likely to reply to messages. They also get

increasingly interactive with other users over the course of a long Twitter session, while the length of an

average tweet decreases during this same time frame. Bots, on the other hand, show no such changes.

SERVO Issue-1.2020 23

Follow the Bouncing Ball

T-Kuhn over at Electron Dust started thinking about

ball juggling machines in 2015. He wrote about his

first attempts at creating them in the Electron Dust

blog post in 2017. He then wrote another post about

his then newest build in 2018. Now, in 2020, the quest

to get a machine to juggle a ping pong ball reliably has

come to an end (as this current build is able to keep

the ball bouncing for hours.)

The machine requires the following components

to work:

• 1x Teensy 4.0 microcontroller running the

code at https://github.com/T-Kuhn/

HighPrecisionStepperJuggler/tree/master/

Arduino/HighPrecisionStepperJuggler

• 4x StepperOnline DM442S stepper motor drivers

• 4x Nema 17 stepper motors with 5:1 planetary gearbox

• 1x 48V 8A power supply

• 1x e-con Systems See3CAM_CU135 camera

• 1x Windows computer with OpenCV installed on it

• All the parts defined in the Fusion360 project described at https://github.com/T-Kuhn/

HighPrecisionStepperJuggler/tree/master/Autodesk%20Fusion360%20data

• The custom Windows Application (made with Unity) described at https://github.com/T-Kuhn/

HighPrecisionStepperJuggler/tree/master/Unity/HighPrecisionStepperJuggler/Build

You can watch it bounce here: https://electrondust.com/2020/03/01/the-octo-bouncer.

Draganfly Drones Do Monitoring

In a rush to combat the global spread of the deadly

coronavirus (COVID-19), Draganfly will deploy “pandemic

drones” to remotely monitor and detect people with

infectious and respiratory conditions to help stop the spread

of the disease.

The Draganfly drones will be fitted with a specialized

sensor and computer vision system that can monitor

temperature, heart and respiratory rates, as well as detect

people sneezing and coughing in crowds and other places

where groups of people may work or congregate.

Draganfly will serve as the global systems integrator

for the Vital Intelligence Project: a health and respiratory

monitoring platform from Vital Intelligence, Inc. The breakthrough technology was developed in a

collaboration between the University of South Australia and the Science and Technology Group

(DST), which is part of Australia’s Defence Department. The project has an initial budget of $1.5

million.

The sensing system uses existing and new camera networks, UAVs, and remotely piloted aircraft

systems for health monitoring and detection of infectious and respiratory conditions, including

monitoring temperatures, heart rates, and respiratory rates.

The drones can monitor people in public crowds, workforces, airlines, cruise ships, convention

centers, border crossings, or critical infrastructure facilities. The technology can also be used to

monitor potential at-risk groups, such as seniors in care facilities.

The Draganflyer

Commander UAV is

a remotely operated

miniature helicopter

designed to carry wireless

camera systems.

Photo courtesy of

Draganfly.

24 SERVO Issue-1.2020

Researchers in Japan developed a drone

equipped with a bubble maker for

autonomous pollination.

Photos courtesy of iScience.

Gonna Burst Your Bubble

While folks around the world are working on different artificial

pollination systems, there’s really no replacing the productivity,

efficiency, and genius of bees. However, researchers at the Japan Advanced

Institute of Science and Technology (JAIST) have come up with an

alternate method of pollination: pollen-infused soap bubbles blown out of

a bubble maker mounted to a drone. And it apparently works really well.

Most other examples of robotic pollination have involved direct

contact between a pollen-carrying robot and a flower. This works, but is

not really efficient since it requires the robot to do what bees do: identify

and localize individual flowers and then interact with them one at a time

for reliable pollination. The problem becomes scaling to cover an entire

orchard.

In a recent issue of iScience, JAIST researcher Eijiro Miyako described

how his team had been working on a small pollinating drone that had the

unfortunate side-effect of frequently destroying the flowers that it came

in contact with. Frustrated, Miyako needed to find a better pollination

technique. While blowing bubbles at a park with his son, Miyako realized

that if those bubbles could carry pollen grains, they’d make an ideal

delivery system.

You can create and transport bubbles very efficiently, generate them easily,

and they literally disappear after delivering their payload. They’re not targetable,

of course, but it’s not like they need to chase anything, and there’s absolutely no

reason to not compensate for low accuracy with high volume.

According to Miyako:

We accidentally found that natural pollen grains can be easily incorporated into a

soap film and flown in the air using various bubble devices.

To show that their bubble pollination approach is

scalable, the researchers equipped a drone with

a bubble machine capable of generating 5,000

bubbles per minute. In one experiment, the method

resulted in an overall success rate of 90 percent

when the drone moved over flowers at 2 m/s at a

height of 2 m.

SERVO Issue-1.2020 25

NEW PRODUCTS36 Tooth Pinion Gear

The 36 tooth 8 mm REX bore pinion gear is now available from

goBILDA. The bore perfectly matches their 8 mm REX shafting to create a positive drive. While little work is left for the set screws, goBILDA put two of them in for good measure.

This particular gear is able to be meshed with an 84 tooth hub gear spaced 48 mm away for a 2.33:1 ratio, or it can mate to a 24 tooth gear to create a very compact 1.5:1 ratio only 24 mm apart. If your build provides the freedom to adjust the spacing between your gears, it’s able to mesh to any MOD 0.8 gear that suits your needs. The counterbore on the top side of the gear allows you to run right up against an 8 mm bearing without the use of a shim. Price is $8.99.

40 Tooth Pinion Gear

The 40 tooth 8 mm REX bore pinion gear is also now available from

goBILDA and perfectly matches the 8 mm REX shafting to create a positive drive as well. There are two set screws.

This gear is able to be meshed

with an 80 tooth hub gear spaced 48 mm away for a 2:1 ratio, or it can mate to a 20 tooth gear to create a very compact 2:1 ratio only 24 mm apart. If your build is able to adjust the spacing between your gears, it’s able to mesh to any MOD 0.8 gear you choose. The counterbore on the top side of this gear allows you to run right up against an 8 mm bearing without the use of a shim as well. Price is also $8.99.

30 Tooth Miter Gear

The 8 mm REX Bore Miter Gear from goBILDA is able to mate with any

other 2315 Series Miter Gear. A miter gear is a specific type of bevel gear.

Two mating miter gears create a 1:1 ratio, and transmit power at a 90 degree angle due to the 45 degree pitch cone angle.

The underneath side of this gear has been dished out to allow a thrust bearing to set the location of the gear (relative to the inside wall of an 1120 Series U-Channel) and counteract the potential spreading forces in the most extreme applications.

Additionally, the 32 mm shelf on the back will allow a 32 mm diameter component such as goRAIL, goTUBE, or a Sonic Hub to nest down in the cavity and fasten with M4 socket head screws. Price is $12.99.

38 mm Pitch Steel Set Screw Sprocket

This 10 tooth sprocket from goBILDA has a 6 mm D-bore to

perfectly match 6 mm D-shafting, as well as the D-shafts used on goBILDA’s 5202 Series Gear Motors. The steel construction provides excellent strength and wear resistance. Price is $7.99.

8 mm Pitch Steel Set Screw Sprocket

This 10 tooth sprocket from goBILDA has an 8 mm REX bore

to perfectly match their 8 mm REX shafting. Its steel construction also provides excellent strength and wear resistance. Price is $7.99 as well.

For further information, contact:

goBILDAwww.gobilda.com

26 SERVO Issue-1.2020

Learning Platform for Arduino

Dr. Duino has expanded its line of rapid learning and prototyping platforms with its latest Explorer edition and

an updated Pioneer version.Building and tinkering with electronics is much easier

with these Arduino compatible shields. They are complete compact learning and prototyping systems which are perfect for anyone interested in electronics.

Designed with the beginner in mind, the Pioneer Edition helps you easily learn about the world of electronics through

hands-on projects. Designed with the experienced user in mind, the Explorer edition helps you build and test your electronic concepts quickly.

It’s jam-packed with powerful features, which include:

• 128x64 line character and graphics OLED• Power options• Bluetooth LE• Prototyping area• Eight channel addressable LEDs• Mini breadboard• And more ...

The Pioneer is Arduino Uno compatible, while the Explorer is compatible with the Uno and Nano versions.

Expansion packs are also available for both the Pioneer and Explorer. Both platforms are currently on sale.

For further information, contact:

Dr. Duinowww.drduino.com

Programmable USB Keyboard Controller Module

Saelig Company, Inc., has introduced the KeyWarrior28: the smallest controller of the

KeyWarrior family with a great deal of functionality that is more than just standard keyboard functions.

The KeyWarrior28 — available as a 3.3V QFN28 chip or DIL28 module — controls up to 64 keys in an 8x8 matrix. Just a USB cable and the keys are connected to the module. The functionality of the keys is programmable via a USB port and stored in internal Flash memory. For instance, it can offer a key-operated mouse function or media and application controls like Play, Pause, Mute, Start Browser, etc.

Each individual key can be programmed with either a single key code, a key code plus a modifier (shift, ctrl, alt, gui), a macro, a mouse function, a media/application control, or an FN key. The two optional FN keys give the ability to switch to a second or third key layout.

Like the modifier keys, FN keys can be programmed to act as ‘locking’ or ‘sticky’ (locking, but only for the next key). This allows mode switching or single finger operation.

Each of the 19 macros can be programmed on to any of the keys. A maximum of 31 key codes can be in each macro. There are three different types of macros. A static macro acts as if all keys in the macro are pressed at the same time. Typing macros activate each code just momentarily. This allows repeating characters, special character use, and upper/lower case in the macro. Cell macros work like the text input on phones with numeric keypads. Pressing the key again removes the last character and replaces it with the next. The KeyWarrior28 works with existing system

drivers and does not require special software. Each unit has a unique serial number and a built-in counter to register the number of erase cycles. KeyWarrior modules and ICs are designed by Code Mercenaries. Pricing starts from $12.20.

For further information, contact:

Waterproof Smart Servos

Tthe DYNAMIXEL XW series of smart servos are ROBOTIS`first line of IP level models, featuring a certified

IP68 rating which means they’re good at one meter for a 24 hour duration. The servos are designed for use in wet environments, underwater, and any outdoor applications where a sealed servo is necessary. The XW series come with a separate waterproof cable and extension cable.

Features include:

Saelig Companywww.saelig.com

Continued on page 72

SERVO Issue-1.2020 27

28 SERVO Issue-1.2020

When I started my journey into building combat robots, I followed a guide published in the

Combat Zone section in one of the 2010 issues of SERVO to build an easy test box out of a steamer trunk.

This test box has served me faithfully for a few years now. However, it could only be used for basic drive testing or static weapon testing. There just wasn’t enough room to really drive around with a weapon running.

As my experience as a builder grew, so did the destructive power of my creations, until the little box couldn’t be relied on to contain them without signifi cant modifi cation.

It was time to build a bigger, better box. I had four goals I wanted to meet with my new box design:

1. I wanted it to be big enough to drive around.

2. I wanted it to be small enough

to be easily stored without disassembly.

3. I wanted it to be able to contain my bots if they smack the wall with the weapon running at full speed.

4. I wanted it to be dead simple to source and build.

The materials used include (https://pastebin.com/ZRVeNz9K):

• 4x 1”x6”x8’ lumber• 2x 24”x48” MDF sheets• 1x 48”x48”x1/4”

polycarbonate sheet• 8x 6”x24” sheet metal strips• 8x corner brackets• 2x utility hinges• 2x latches• 1x handle• 120x #8x3/4” screws

With the exception of the polycarbonate sheet, all the supplies could be obtained with a trip to my local hardware store.

The entire set of materials costs less than $300, with 70% of that cost being for the polycarbonate and metal

sheets to contain the power of the spinning weapons.

Construction

1. Cut the boards into eight 47.25” lengths.

2. Pre-drill and screw the corner brackets onto one end of each board.

3. Pre-drill and screw four of the boards together to make two 4’ square boxes.

4. Lay the polycarbonate on top of one of the boxes, then pre-drill and screw it to the top of the box, with the screws 12” apart at most.

5. Lay the two sheets of MDF on top of the other box (soon to be the bottom), and drill and screw them to the box like the polycarbonate. Then, fl ip the box over.

6. Drill two holes near each end of all eight sheet metal strips; close enough to be screwed to one of the bottom boards.

7. Pre-drill and screw all eight sheet metal strips to the inside of the MDF-fl oored box, with two strips overlapped to fi ll each side.

Building a Better Box

FEATURED FEATURED

THIS MONTHTHIS MONTH

28 Building a Better Building a Better

BoxBox

30 Stepping Stones — Stepping Stones —

The Story of Thunder The Story of Thunder

ChildChild

33 Bringing About the Bringing About the

ApocalypseApocalypse

By Ryan Clingman

Corner bracket installed on the end of a cut board.

SERVO Issue-1.2020 29

8. Lay the top box on top of the

bottom box.

9. Mount the hinges on the back

side where the two boxes meet,

12” from the ends.

10. Mount the latches on the front

side where the two boxes meet,

12” from the ends.

11. Mount the handle in the middle of

the front side of the box.

Congratulations! You’ve created

a simple and sturdy test box that

only required cutting a few boards to

length and screwing it all together!

The steel reinforced corners and

inner frame combined with the 1/4”

polycarbonate should make this test

box strong enough to survive rigorous

testing up to the Beetleweight class.

The inside is over 7” tall, which

should accommodate the majority of

Beetleweight designs, and the floor

space is enough that it could even be

used as an arena for 150g bots.

Happy testing! SV

To post comments on these

articles and find any associated

files and/or downloads, go to

www.servomagazine.com/

magazine/issue/2020/01.

Boards assembled to form a box.

Completed steel-reinforced

test box.

30 SERVO Issue-1.2020

After my first event in late

2012, I decided to get

started in the world of

Beetleweight combat

robots. Since I had no

fabrication skills or access to any

tools, one of my friends suggested I

purchase a kit from kitbots.com.

After looking at their selection, I

chose the chassis for a four-wheel brick

based on the Beetleweight Trilobite as

my introduction into the class.

After getting all the necessary

electronics and hardware, my dad

and I assembled it on the dining room

table a week before its first event:

Motorama 2013. The bot was named

Thunder Child, which came from the

fictional ironclad warship in H.G. Wells’

War of the Worlds.

The bot didn’t do so well. The

ESCs I purchased were too big for the

bot and drew way too much current,

which resulted in most of my bot’s

motors burning

out throughout

the competition.

Despite this issue, Thunder Child

managed to finish with a 1-2 record,

and won a grudge match held during

downtime.

After the event, I was given a lot

of advice from fellow builders. Thunder

Child would go on to compete at a

few events over the next two years

where it achieved minimal success,

usually getting knocked out of the

tournament with a single win.

The turning point for Thunder

Child came in summer 2015, when

another builder that lived 30 minutes

from me offered to help me out by

Stepping Stones —Stepping Stones — The Story of Thunder The Story of Thunder ChildChild By Nate Franklin

The new wedge didn’t last long, but it was a step

in the right direction.Thunder Child at its first event.

SERVO Issue-1.2020 31

making a steel wedge for Thunder

Child. With the kit’s CAD files freely

available for reference, he was able to

design a new attachment and taught

me how to make it. It was my first real

experience working with tools, but the

wedge turned out nicely.

The work paid off, and Thunder

Child placed third at Bot Blast 2015,

with the wedge coming in handy

when dealing with horizontal spinners.

Unfortunately, Thunder Child would

struggle in the next two events,

resulting in the wedge I had built

getting destroyed by a nasty vertical

spinner.

In 2016, Thunder Child found

success when Pete Smith (the owner

of Kitbots) sold me a wedge from the

BotKits D2 kits modified to fit Thunder

Child. I managed to pull off an

undefeated run at Bot Blast, and place

second at SWORD later that year.

The wedge worked extremely well

against horizontal spinners but was an

easy target for the new meta: vertical

spinners with wedglets.

I found the solution to the

problem when BotKits released their

Wolverine claws in 2017: S7 tool

steel wedglets designed for fighting

vertical spinners and other wedges.

After finding out that the claws used

the same size hole for the mounting

that the Trilobite kits use, I instantly

purchased a pair.

With Thunder Child now able

to swap to different attachments

depending on the opponent, I chose

to replace the stock titanium axle with

shaft collars with a grade 8 hex bolt

and lock nut.

This allowed for easier attachment

swapping since I didn’t need to worry

about applying Loctite to any set

screws. However, it came at the cost

First place and best driver at Bot

Blast 2016 with the D2 wedge.

The anti-D2 wheels (only used

once) and wedglets.

Original titanium axle and shaft collars (top) and new grade 8 bolt

and lock nut (bottom).

32 SERVO Issue-1.2020

of an additional ounce in weight.

Thunder Child entered 2018 by

placing fi fth at Motorama, stopped

only by a broken soldering joint. Things

were looking up, as I had also started

learning computer-aided design (CAD).

My fi rst big project for Thunder

Child was creating a set of wedglets

designed to fi ght D2 kits, which had

become increasingly popular in the

Northeast. In addition, I came up with

an anti-D2 confi guration, where I could

swap Thunder Child’s normal snap

hubs for longer hubs that would fi t an

additional wheel for extra traction.

Bot Blast 2018 was my fi rst event

with the three attachments (wedge,

claws, and wedglets), and proved

to be a huge learning experience. I

lost my fi rst match with the anti-D2

confi guration, where one of the set

screws came loose and a wheel fell

off.

In addition, the bot shut off at the

end of the fi ght, likely due to the new

speed controllers drawing too much

current like what happened at its fi rst

event. Despite this, I managed to fi ght

through the loser’s bracket, utilizing all

three of the attachments to place third

after experiencing similar electronics

failures.

After solving the electrical

gremlins, Thunder Child came back

stronger than ever, placing at the next

two events and fi nishing in fourth

place at Motorama. I then took the

bot overseas to the UK Beetleweight

web series, “Bugglebots,” where it

placed second in a fi eld of 30 bots

from around the world and became a

fan favorite.

The only change in 2019 was

swapping to the faster 22 millimeter

motors and a brand new Futaba

transmitter. These upgrades resulted in

Thunder Child placing fi rst twice, much

to my delight.

After placing seventh at

Motorama 2020, I felt it was time

for a change. I took all the skills I

had learned in CAD and built a new

Thunder Child from scratch. My

original kit had done its job. It served

as a stepping stone into the world of

designing combat robots. SV

Fighting Claws 2 at Bugglebots.

A render of the new Thunder Child. Coming soon to an arena near you!

SERVO Issue-1.2020 33

Portable Apocalypse is

my current bot in the

3 lb category, and it’s

an undercutter with a

powerful single tooth

disk. The bot has gone through four

major iterations, with each new

version seeking to improve on the

performance and shortcomings of the

previous versions.

Version 0 of the design began as

a scaling-up of my 3D printed 1 lb bot

design, Someone Else’s Problem. This

meant that I 3D printed the frame

as a solid chunk of glass-filled nylon,

and then supplemented with UHMW

plastic for armor to protect the wheels.

Unfortunately, life happened, and

it never saw competition. While I was

waiting for the opportunity to make

it to another competition, I slowly put

together the design for Version 1 of

Portable Apocalypse.

The overall shape remained the

same, but my discovery of metal laser

and waterjet cutting services inspired

me to make the frame out of metal

instead; 2 mm titanium works great

for the wedges for the popular D2 kits,

so why not make your bot out of that?

The main structure of the whole

bot comes from its top and bottom

plates. Aluminum standoffs between

the plates provide the rest of the

structure, and the standoffs can

be press-fit into 3D printed walls to

contain the electronics, as well as

giving something to mount the motors

and armor to.

Due to the space constraints

inherent in making an undercutter,

there weren’t a lot of parts that were

ideal for dealing with both axial and

radial forces in a small package.

Bringing About the Apocalypse By Ryan Clingman

Portable Apocalypse

version 1, featuring a

titanium frame.

Portable

Apocalypse

version 0, with a

3D printed frame.

34 SERVO Issue-1.2020

So, I wound up making my

own unique bearing setup. There’s

a bearing in both the disk and the

pulley, with a nested pair of washers

squeezed between

them to help

handle axial loads

on the weapon

disk.

I can really tighten the shoulder

bolt shaft down hard to lock the inner

races of the bearings together and

make the frame nice and tight, while

still leaving the outer races and the

weapon disk free to spin.

Slots in the 3D printed pulley let

me put in square nuts to clamp the

pulley to the disk.

After some issues I had with the

weapon of the earlier versions of my

1 lb bot flexing enough to damage its

own pulley, I designed it so that the

disc is always directly over the weapon

motor and pulley.

This way, even if the weapon

flexes, it just rubs on the pulley instead

of having the chance to bite into the

pulley and risk disabling itself.

I designed all this so that (with the

exception of the weapon shaft and

power switch) I would only need one

size of hex wrench to fully assemble/

disassemble the entire bot.

All the 6-32 screws for the frame

use a 5/64” hex drive, and all the

metric screws for the motors need a

2 mm hex drive, but the two are so

3D printed walls combine with the standoffs

to complete the electronics compartment and

provide mounting points for the motors and

armor.

The weapon shaft setup allows the center of the

bearings to be clamped to the frame while leaving

the outer part free to spin with the disk and pulley.

The two metal plates combined with some standoffs form the key

part of the frame.

SERVO Issue-1.2020 35

close together that I can use one hex

wrench for all of it.

Portable Apocalypse v1 performed

fairly well at the NERC Franklin

Institute 2019 event at least in terms

of offense and durability, but the

competition also served to highlight

several points in the design that could

be improved on.

Portable Apocalypse v2 may look

much the same on the outside, but

every part on the inside got changed

out.

I learned that having to

completely remove the top plate to

get the battery out for charging was

more annoying than anticipated,

so I made the lid for the electronics

compartment its own separate part.

Not needing to completely remove

the top plate also means that the

weapon motor can simply be mounted

directly to the top plate instead of

needing to find a funky way to mount

it off the bottom plate.

The other problem with the

electronics compartment of version

1 was that I apparently failed to

leave enough room for all the wires,

leaving me to play a rousing game of

spaghetti Tetris every time I took the

battery in and

out. To alleviate

this, the height

and length of

the electronics compartment were

increased slightly to provide much

needed space for wire routing.

Version 1 of the design used

a combination of heat-set inserts,

nutstrip, and Actobotics parts to

attach the wheel guards and drive

motors to the frame.

After seeing the apparent success

of the technique in the EndBots

Vector kits, I decided to change to

using square nuts press-fit into the

Portable Apocalypse Version 2,

with aluminum frame for a less

expensive option.

In Version 2 onward, square nuts pressed into the

printed walls provide all the horizontal attachment

points for the frame.

The disk is designed to always be over the

weapon motor to avoid having it deflect into the side of the pulley and damage it.

36 SERVO Issue-1.2020

3D printed parts to attach these parts

instead.

At the time of building, I had

some inklings of trying to turn the

design into a kit to sell, so I also tried

to reduce the cost and complexity of

the parts where I could.

The titanium frame plates were

replaced with thicker aluminum ones;

the DIY brushless gear motors were

replaced with off-the-shelf brushed

motors; and I tried out some cheap

Chinese brushed ESCs. All of it

performed admirably.

After a respectable showing at

NERC’s Motorama 2020 event, I have

now built Portable Apocalypse v3 with

the goal of achieving a spot on the

podium the next time around (no small

feat when the competitions I frequent

have 30-60 competitors to overcome

to get there).

With the v2 design working well,

the changes were relatively minor this

time.

While the aluminum frame

worked great, I have switched back

to a titanium frame for the best

durability. What lost me both matches

and knocked me out of the previous

tournament was my receiver slowly

failing due to repeated impacts.

Wrapping all the electronics in

foam should help to abate the impacts

and increase the lifespan of the parts.

Bringing Portable Apocalypse

to this point has been a measured

process of evolution in the design,

addressing fl aws in the design as well

as looking at the building techniques

that have worked well for others

and, incorporating them into my own

designs.

Only time will tell if it will come

out on the top of the pile, but I plan

to keep improving it until it gets there!

SV

Make Precision Metal Projects

User-friendly, budget-friendly,

making-things-happen-friendly.

The compact Tormach PCNC 440

runs on single-phase power and

fits just about anywhere.

The pre-configured Starter Package

is priced to run at $7,176.

Build yours at tormach.com/440/loop.

Portable Apocalypse Version 3 — back to titanium and better

than ever.

GearBox

Get Your Robot Ru� in’!

THE MOST COMPLETE PROGRAMMING TUTORIAL!� Everything you need to learn the fundamental concepts of PIC® microcontroller programming, including:

•Program Flow•Loops•Coding Techniques•Binary Manipulation

•Device-To-Device Communication•User Interface Design•In-circuit Debugging•And More!

� Includes all the necessary software, compiler, trainer board, cable, tutorial with exercises and sample code!

Check out our other popular productsfor PIC® developers including:

U2 Programmer•PBP3 CompilerPrototyping Boards•Experimenter Boards

Contact us at info@melabs.com

$99.99

SERVO Issue-1.2020 37

38 SERVO Issue-1.2020

SERVO Issue-1.2020 39

Bot Ross is an easy-to-use machine capable of

turning an image from your computer into

an accurate sketch. Driven by a PIC32MX

microcontroller, two H-bridge circuits for

controlling stepper motors, and a serial

communication interface with a Python script run on any

computer, you can see Bot Ross come to life.

It draws with a pen attached to a servomotor controlled

rack and pinion mechanism to move the pen up and down,

which moves in two dimensions using stepper motors which

turn threaded rods.

With a careful control algorithm, a linear interpolation

of the desired image can be drawn in roughly 10 minutes.

It works with any image you upload to the system, meaning

infi nite masterpieces await.

Electronics

To give Bot Ross the ability to think, we needed to add a

brain. While there are many different options for control, we

decided to go with a PIC series microcontroller which would

give us all the computing power we’d need to draw and

store images.

The PIC is a fi ne microcontroller, but we needed to fi rst

install it onto a printed circuit board (PCB) where it could

receive power, distribute signals, and connect to a laptop.

On the PCB, we added a port expander, which gave

the PIC an extra 12 input/output pins; a color LCD display

so that we could debug our programs; and fi nally, a low

current power supply to give power to just the components

on the PCB. This board ran the C code we wrote to operate

the stepper motors and drawing algorithm.

Responsible for Bot Ross’s entire range of motion, the

motors needed to be precise and accurate — much like

the arms of his namesake. We decided to go with stepper

motors as they offered not only accuracy but also range of

motion.

Stepper motors are a special kind of motor, containing

tiny “steps” that you can power. This means that the motor

is essentially quantized into small, precise values which are

easy to program. When you apply a voltage to each of the

“steps” — controlled by two coils of wire called inductors —

the gear on the inside aligns, turning the motor by a small

degree. By applying specifi c patterns to the motor, Bot Ross

would be able to precisely move to any location on the

paper.

Much like a human bicep that is bigger than the

forearm, we used two different sized motors so that one

motor could support the weight of the other. Just like the

bicep, the big motor would not only have to move up and

down the page, it would also have to carry around Bot

Ross’s “hand” which held the other stepper motor and the

pen.

Stepper motors (while very accurate) take a lot of power

to operate — too much for our microcontroller to directly

supply. The good news is, our microcontroller doesn’t have

to actually do the heavy lifting. It just has to act as the

operator.

Using H-bridges, we can control the fl ow of current

through each of the motor coils that act as electromagnets.

Meet Bot Ross

Between the three of us, as engineering students, drawing just

isn’t something we’re any good at. Fortunately, we are good at

engineering. So, by extension, being good at engineering means

we’re actually great at drawing. That is, after we build a robot to draw

things for us! Enter Bot Ross: the ever-precise robot built to draw any

picture your heart desires (as long as you can fi nd a version of that

picture with a quick Google image search, of course).

By Sam DiPietro, Brett Sawka, and Rohan Shah

40 SERVO Issue-1.2020

By alternating the

direction of current

fl ow in each coil, the

electromagnet can

be activated in such a

manner that the shaft

rotates in discrete

amounts.

The current

direction in each coil

also dictates whether

the motor turns

Figure 1: H-bridge current fl ow.

Figure 2: Schematic of main board.

SERVO Issue-1.2020 41

clockwise or counter-clockwise. This is shown

in Figure 1. A full schematic of the system is

shown in Figures 2 and 3.

Coding It UpThe software side of Bot Ross comes in

three parts, each of which work together to

drive the entire system. We have our motor

control code, which is needed to work with

our circuitry to get the steppers moving and

our servo to lift the pen up and put it down.

With that established, we needed a script

to process images, formatting image data

in a way that works well with our motor

controlling code. This script also includes

our method of communicating that image

data from a computer to our PIC32MX

microcontroller.

Finally, the most visible part of our code

comes with the control algorithm, which

interfaces the data sent over by our image

processing script with our motor control code.

When it all comes together, we have everything we need to

get Bot Ross to draw some pictures.

When starting to code, we fi gured the best place to

begin was with getting our motors moving, since a robot

that can’t move wouldn’t do a whole lot. With our motor

controller circuitry already built, we dug into determining the

right inputs to that circuitry to accomplish three main things:

spin a motor at the right time; turn it the exact right number

of degrees; and get it to spin in the direction we wanted.

To make stepper motors move, they require two

carefully timed pulse pairs coming from our microcontroller

to the H-bridge inputs. A “pair” of pulses in this case involves

two pulses which are exactly opposite each other; meaning

when one pulse is on, the other is off, and vice versa.

We needed to generate two of these pairs, one of

which was offset from the other by exactly half the length

of a pulse. This is best described using a diagram like the

one in Figure 4.

Since timing is key, the best way to generate

these pulses was to use one of the PIC32MX’s

periodic interrupt timers. We can load the hardware

timer with some value (corresponding to an amount

of time), and it counts down to zero while other code

runs on the CPU. Once the timer reaches zero, it

interrupts whatever code is currently running in order

to do something else.

In our case, that “something else” was to turn

on or off the GPIO pin used to send out pulses.

This chunk of code — called an interrupt service routine

(ISR) — would fl ip pins on or off to create the pulse form

above. If we were to let the ISR do this every single time it

was triggered, that would mean the attached motor would

always be moving in the same direction. We needed a way

to change direction, and only move when we wanted to.

We accomplished both these things by setting up some

global control variables for controlling our two motors.

This gave the ISR a way to check whether the user (or the

picture-drawing program) actually wanted the motor to

move. Figuring out the direction worked similarly.

We could tell the ISR whether the motor should spin

clockwise or counter-clockwise, and it checks every time. If

the direction variable is a 1, the motor spins clockwise with

the ISR-generated pulses shown above. If it’s a 0, the ISR

uses the below waveforms to make the motor spin counter-

clockwise.

Figure 3: Schematic of stepper drivers.

Figure 4: Stepper motor control signal waveforms.

42 SERVO Issue-1.2020

With all this established, it was time to fi gure out the

system for actually drawing pictures. Since each drawing

is basically just a map of X-Y coordinates, we needed to

fi gure out exactly what one coordinate meant. We ended up

deciding that each coordinate — corresponding to one pixel

on an image — would be 1 mm by 1 mm.

Our motor control code could easily support drawing

millimeter-long lines, which gives picture drawing great

precision. With our motors controlled and a convention for

how an image should appear, we now needed a way to get

pictures involved. This required a script for image processing,

or having a computer look at a picture and turn it into arrays

of numbers.

The goal here was to break an image down to a map of

X-Y coordinates, then fi gure out the best way for Bot Ross

to connect the dots in that map. Since images would be

coming from a computer rather than the microcontroller, we

decided to write this part of the code using Python to take

advantage of easier-to-use arrays and the OpenCV library for

computer vision and image processing.

Using OpenCV, we can use an algorithm called the

Canny algorithm to do an edge detection of an image. An

“edge” is any kind of boundary that you can see between

shapes in an image. This algorithm takes an image and

creates that X-Y map of edges.

With that 2D map of the image’s edges, we wrote

an algorithm suitable for Bot Ross to draw the image as

effi ciently as possible. The algorithm starts at the top right

of the X-Y map and fi nds the fi rst coordinate where an edge

actually is. The stepper motors turn on, move the pen to the

right point, and place it down on the paper.

Next, Bot Ross looks for any adjacent points which need

to be drawn. If there is one, the pen moves there, drawing

the fi rst little bit of the picture. Then, the algorithm looks for

points adjacent to that point.

This process continues until it fi nds an “end” point with

nothing adjacent to it. When that happens, the pen goes up

and it retraces its steps, fi nding any points that had another

adjacent point which weren’t drawn the fi rst time. The pen

goes down, and the process happens again, just with a new

starting point. This same process happens over and over,

until the pen is back at that very fi rst point without any

adjacent points to draw.

By now, there should be some lines and curves, all

connected to each other. To keep drawing, Bot Ross starts

over. It fi nds a new undrawn point, places the pen, and

looks for adjacent pixels. With this algorithm running over

and over (and over) again, eventually every single pixel will

be found and the entire image will be sketched.

This process is based on a common algorithm called

depth-fi rst search2, which is often used for robots to

traverse their surroundings. In this case, we used it to give

instructions for a robot to draw a picture.

With software and hardware in place, it was time to

perfect the mechanics behind picture drawing.

The Build

We spent a lot of time writing code and designing

circuitry to make the plotter run well, but to put it all

together in one system, we needed to physically construct

Bot Ross. The system had three degrees of freedom; two of

which were the stepper motors moving along the X and Y

axes, with the third degree being the pen moving up and

down. Take a look at Figure 5.

An important part of using the stepper motors was

Figure 5:

Physical design

block outline

(right) and

construction

(left).

SERVO Issue-1.2020 43

having a method of turning their rotational motion into

linear motion. This was done using two lead screws which

are similar to threaded rods, and allowing the turning

motion of the stepper motors to become linear motion.

Since the stepper motors only have a metal shaft to use

for any kind of fi xture, collars were needed to connect the

lead screw to the motor. Also, each lead screw has a nut

which connects to the object that is moving across the axis.

For the big stepper motor, the nut was attached to the

smaller arm that held the second smaller motor. For the

smaller stepper motor, the nut was attached to the block

that held the actuation mechanism for the pen.

While one end of the lead screws was fi xed to the

shaft of the stepper motors with collars, the other ends

were held in place at a level height by custom 3D-printed

screw holders. These holders were essentially blocks, with

openings to allow the screws to be propped up instead.

To allow the smaller arm to move smoothly when the

big motor was stepping, we used a drawer slide (Lowe’s

item #380974) to reduce the frictional resistance on the

arm when moving. These slides are mechanisms found in

drawers pretty much anywhere. They’re basically rails with

supporting wheels that allow the support to move across it

with little friction.

This reduction of friction was important due to the

nature of our design. Any friction on the free end of the

smaller motor arm would cause “missed” drawing as the

arm would bend without the pen moving the specifi ed

distance. We sprayed WD-40 on the drawer slide as well to

ensure the support was not sticking to any part of the slide

rail when moving the entire distance across.

To make the pen move up and down, a 3D-printed

rack and pinion mechanism obtained from the Thingiverse

website was used in conjunction with a micro servo to allow

the pen to move linearly up and down. This mechanism

was a highly important component to our project because

it allowed us to fi ne-tune the position of the pen when

drawing. We wanted our artistic creation to be great!

A rack and pinion works similar to the way the lead

screws work in our project. The pinion is a gear that

attaches to a servo, and when it rotates, it moves the rack

holding the pen. Refer to Figure 6.

Figure 6: The rack and pinion mechanism.

ITEM QTY

Threaded Rods 2

Stepper Motors 2

Shaft Couplers 2

Drawer Slide 1

Big Board 1

Port Expander 1

MicroStick2 1

PIC32MX 1

Jumper Cables 19

Header Pins 8

Dual H-Bridge Motor Drivers (four pack) 1

PLA for 3D Prints

Link to Project Web Page: http://people.ece.cornell.edu/land/

courses/ece4760/FinalProjects/f2019/bas335_rns85_sdd58/

bas335_rns85_sdd58/bas335_rns85_sdd58/index.html

Link to Project Video: https://www.youtube.com/

watch?v=UoiOHu-NbZk&t=3s

OpenCV Python Library: https://opencv.org

Explanation of Depth-First Search: https://en.wikipedia.org/wiki/

Depth-fi rst_search

Rack and Pinion 3D object fi les: https://www.thingiverse.com/

thing:3170748

Richelieu 20” drawer slides (purchased at Lowe’s): https://www.

lowes.com/pd/Richelieu-2-Pack-20-in-Drawer-Slide/50041730

Microchip Documentation on Stepper Motors: https://www.

microchip.com/stellent/groups/SiteComm_sg/documents/

DeviceDoc/en543050.pdf

Parts List Resources

44 SERVO Issue-1.2020

The fi nal part of the construction was attaching

everything to the wooden base. This project was done

with a relatively small budget, so we resorted to the cheap

(yet very effective) method of hot gluing to attach all the

components onto the base.

As we later noticed, this wooden base was quite

warped from its previous use, so we had to place another

platform on the base with small supports underneath to

create a level drawing surface.

Happy AccidentsAs with all engineering projects,

problems and bugs arise mid-build

and need to be addressed. Nothing is

ever perfect on the fi rst try, and Bot

Ross was no different. For the fi rst

few runs of Bot Ross, the robot would

slowly start drawing the image over

itself, getting lost on the large page.

Thankfully, we included an

onboard display which allowed Bot

Ross to tell us that it thought it was in

the right position. Figure 7 shows an

image of the distortion that we kept

on noticing.

No matter what we tried, we

couldn’t fi gure out why the image

Figure 8: Original image of Elon Musk (left) and drawn image of Musk (right). The left image by Duncan.Hull is licensed under CC BY-SA 4.0.

The image by Duncan.Hull is shown cropped in Figure 8 as that was the optimal aspect ratio determined to be used for the plotting system. The

image was not modifi ed in any form other than cropping.

Figure 7: Distorted image (left) and

corrected image (right).

SERVO Issue-1.2020 45

would keep on shifting to the left. It wasn’t until the late

hours of the night that we fi nally fi gured out what was

plighting Bot Ross. Just like having a proper canvas to paint

on, we realized that Bot Ross didn’t have a level surface to

draw on.

When the pen was down and moving to the right

(uphill), it would go slower than if it was drawing downhill.

However, this proved to be no problem as it was constant

and calibrated out.

By simply adding a correction factor — an additional

step for every 10 going uphill — we were able to counteract

the force of going uphill and re-center the drawing.

As stated, in all projects bugs are going to appear, and

it was extremely useful for us to have accounted for the

potential for bugs from the get-go with the inclusion of the

debugging terminal.

The MasterpieceAfter weeks of long hours spent in the lab, we did it.

We had fi nally drawn a complete image. We fi nally drew a

picture of the tech mogul, Elon Musk (Figure 8).

Due to the constraints of the plotter, the edge detection

algorithm was run on only the upper portion of the digital

image, as shown by the drawing.

Although the contoured version of the image doesn’t

look exactly like the original, almost all of the portrait outline

and facial details are captured. The suit is the most clear

part; you can even see the outline of his collar.

Since the stepper motors were not that fast, it took

about 15 minutes to draw the picture of Musk, but the time

was different for every image. The aspect ratio of the drawn

image is slightly different from the original, but that could

be easily fi xed by adjusting the number of steps between

coordinates in the X and Y axes.

We learned a lot from the challenges this project

presented and succeeded in creating a “masterpiece.”

Designing Bot Ross was a rewarding experience in

collaborating with a team towards a common goal and

learning how to effi ciently use resources to make a great

project. SV

To post comments on this article and fi nd

any associated fi les and/or downloads, go to

www.servomagazine.com/magazine/issue/2020/01.

46 SERVO Issue-1.2020

Building Building a Linear a Linear ActuatorActuator

While doing some thinking

about building a walking bird

robot, I researched purchasing

linear actuators. What I found is

that linear actuators are fairly

expensive — especially if you’re

an amateur robot builder with

a limited budget. This led me to

thinking about what it would take

to build my own linear actuators.

By Theron Wierenga

SERVO Issue-1.2020 47

A linear actuator functions very simply. By powering

the DC motor, the arm moves out linearly; by

reversing the polarity to the DC motor, the arm

moves in. Circular motion is turned into linear

motion. A linear actuator is a simple on and off

device with no control over the position of the arm. To avoid

extending the arm too far in or out, limit switches are often

used which must be continually read by a microcontroller.

A servo linear actuator is a more complicated device.

However, it does have the ability to position itself. This can

be done through the use of servo motors or DC motors that

have feedback or encoders attached to them or by sensors

to control positioning. My requirements included simple

positioning.

The arm needs to move out to position X and then

return to position Y, with some speed control. This could be

done with limit switches at the needed positions and pulse

width modulation (PWM) to control the speed.

Some further thinking and a few sketches later, the

idea of using Hall-effect sensors instead of limit switches

was added to my plans. A square tube within a square tube

was envisioned, to be 3D printed, forming an actuator arm

within a body.

At the back end of the inner arm is a captured 1/4 - 20

nut, and just outside the back end of the square body is a

captured ball bearing connected to a threaded 1/4 - 20 rod

that moves the inner arm by turning in the captured nut.

This ball bearing is 9/32 inches wide with an outer

diameter of 3/4 inches and a 1/4 inch inner diameter. The

bottom of the inner arm tube has two circular holes at the

ends to press-fit 8x3 mm neodymium disk magnets. The

bottom of the square body has slots in it to hold small Hall-

effect 3144 sensors. Refer to Figure 1.

A single Hall-effect sensor on the bottom (at the

forward end of the outer body) can sense the magnets at

each end of the inner tube. This then becomes the limit

switches but without the mechanical complications of micro

switches. If additional specific positioning of the inner arm

is desired, additional Hall-effect sensors can be added in the

slots.

The complications of this design would be difficult

for the amateur builder if it were to be constructed from

something like aluminum tubing. Fortunately, 3D printing is

a natural for this design and solves a number of construction

challenges. Plus, it allows for accurate sizing and alignment.

Refer to Figure 2.

Selecting an appropriate DC motor was a challenge, but

I was fortunate in my first choice. Electronic Goldmine has a

small surplus Johnson brand DC motor (#G9332), reportedly

1-1/16 inches in diameter, 1-1/2 inches long, 6-24 volts,

and with a 1/16 inch shaft. The shaft turned out to be .090

inches not .0625.

Because some spur gears are available for 1/8 inch

shafts, I increased the shaft diameter by gluing 1/8 inch

Figure 1. Concept diagram, top view.

To post comments on this article and find

any associated files and/or downloads, go to

www.servomagazine.com/magazine/issue/2020/01.

48 SERVO Issue-1.2020

diameter thin wall brass tubing to the shafts with

marine epoxy. This worked quite well and doesn’t

appear to have added any vibration. I measured

the no-load current of this motor to be about 160

milliamps and the stall current three amps.

For gears, I ordered a number of 48 pitch Traxxas

spur gears with 12, 21, 26, and 31 teeth and an 1/8

inch shaft size from Amazon. Some experimenting

was done with the Hobbypark 17, 21, 26, and 29

teeth gear set from Amazon. The Traxxas gears run a

lot smoother.

There are other sets available with differing

numbers of teeth. With different combinations of

these gears, one can increase or decrease the speed

and torque of the motor. For each pair of gears,

the only change in the design is the height of the

center line of the motor. Spur gears must be carefully

aligned, and any misalignment will cause loss of

power, wear, and noise. My goal was to have the

linear actuator be able to have a speed of 50 mm/sec. Using

the 17-tooth gear on the motor and the 26-tooth gear on

the shaft, it averages 84 mm/sec with no load. Having the

arm lifting a 550 gram load, it averaged 67 mm/sec. Refer

to Figures 3 and 4.

Another motor considered was a Tsiny TRS-550PC from

www.tsinymotor.com and available on Amazon. This

motor is considerably larger at 37-1/2 mm in diameter and

64-1/2 mm long. With a 12 volt power supply, the no-load

current is 1.35 amps; nominal current is over 10 amps; and

stall current is a whopping 76 amps.

When I clipped leads onto this motor from a 12 volt

lead acid battery, I wasn’t holding the motor very tightly in

my hand. On start-up, it jumped out of my hand. This would

be a good candidate for some heavy lifting.

It will need a hefty motor driver as well; something like

the BTS7960. While it’s advertised as a 43 amp driver, this is

not a continuous current rating. At 20 amps continuous, this

driver will run very hot.

Construction

The majority of time spent on this project was designing

the 3D models for the parts and then getting them to print

at the exact sizes needed. 3D plastic shrinks on cooling and

a 1/4 inch hole ends up being something like 0.243 inches.

This will vary depending on the brand of plastic used and

even the color in some cases.

PLA was chosen for its ease of use. One can estimate

the shrinkage for the various types of plastic, but nothing

works better than printing, testing, measuring, and printing

again. It’s very important to get all the parts to fit snugly

and be well aligned. All the moving parts need to be able

Figure 4. Inner arm, bottom view with circular openings for magnets.

Figure 2. 3D model from Sketchup, without the top pillow block to hold the captured ball bearing in place.

Figure 3. Inner arm, top view without top cover.

SERVO Issue-1.2020 49

to glide smoothly without binding

or drag. My models went through

many iterations for different designs

and sizes. The stroke length on my

model is 3-1/2 inches or 88.9 mm.

This can be easily lengthened or

shortened by changing the length

of the inner and outer tubes and

the threaded rod. Included in the

downloads are all the Sketchup files

and their object files for 3D printing.

I used Cura 4.6.1 for my slicer.

After 3D printing the inner arm,

a 1/4 - 20 stainless steel nut was

inserted into the capture space and

then the cover screwed down with

1/4 inch 4-40 flat head machine

screws. The two magnets are then

press-fit into the openings on the

bottom. Be sure you have the

correct side of the magnet facing

out for the Hall-effect sensor.

A 6-1/4 inch piece of 1/4 -20

threaded rod was cut and the end

turned down to 1/8 inch to accommodate the spur gear.

Double-check the length of the threaded rod because if it’s

too long, it can hit the end of the inner tube before the

Hall-effect sensor reacts to the magnet. A small lathe is

necessary to get good alignment. Care must be taken not to

crush the threads of the threaded rod with the lathe chuck

jaws.

The threaded rod gets a 1/4 - 20 nut, a 3/4 inch

diameter ball bearing, a 1/4 inch lock washer, and a final

1/4 - 20 nut. I used stainless steel for the nuts and lock

washer. This assembly is then placed into the capture area

at the back end of the outer tube. It’s held in place with a

3D printed pillow block that is held down with four 4-40 flat

head machine screws 5/8 inches long. With the chosen gear

placed on the end of the 1/8 inch axle coming out of the

threaded rod, the assembly should turn easily with very little

friction. Refer to Figures 5 and 6.

There is an inherent problem here with alignment. While

the ball bearing inner diameter is close to 0.25 inches, the

threaded rod is not; it’s something like 0.232 inches. When

the two 1/4 -20 nuts are tightened down, the threaded

rod will not be aligned with the center line of the bearing

opening, causing vibration.

To improve this, I coated

the portion of the threaded

rod that goes inside the

bearing with marine epoxy.

This blob of epoxy was then turned down on a lathe to 0.25

inches to fit snugly in the bearing. This aligns the threaded

rod better with the bearing. Several different models were

built; some with an attached motor mount and others with

separate motor mounts. A separate motor mount allows for

only changing the motor mount when different size gears

are used. The gears were left exposed, but additional walls

could be added to enclose them. It would also be fairly easy

to upscale this design with larger tubes, thicker walls, and a

more powerful motor.

A model with the motor directly attached to the

threaded rod is shown in Figure 7. The shaft coupling used

is a 3 mm to 3 mm flexible coupling 25 mm in length and

18 mm diameter (found on Amazon). The 3 mm holes

were drilled out to accommodate the 1/8 inch shafts. This

diameter is only about 0.007 inches larger.

This version performed better than expected. Using

the same G9332 motor, the no-load speed was 93 mm/sec

and with the 550 gram load 77 mm/sec. The use of geared

drives allows for more torque when gearing down, and

therefore high lifting power. With a direct drive, one does

not have that option. With the use of PWM to a direct drive

or spur geared motor, the speed can only be reduced and

with a loss of torque. Refer to Figure 8.

Figure 8. Drive type variables at full power.

Figure 7. A direct drive model, with the pillow block in place over the bearing.

Figure 5. Threaded rod assembly.

Figure 6. Model with separate motor mounts before installation of the pillow block over the ball bearing.

Direct Drive Spur, Geared Down Spur, Geared Up

Torque (Lifting Power) Fixed Higher Lower

Speed Fixed Slower Faster

Noise Lower Higher Higher

50 SERVO Issue-1.2020

Spur gears are known for their noise and a direct

drive improves this. Helical gears would be another option,

although I had difficulty finding small ones in the sizes I

wanted.

Motor Driver and Hardware

An L298N motor driver (Figure 9) was used to power

the motor. These are widely available and inexpensive.

Two DC motors can be driven from one of these modules

and it can handle 25 watts or about two amps using a

12 volt battery for power. These modules can be digitally

programmed to run a DC motor forwards or backwards, and

can also use PWM to vary the speed of the motor.

A simple circuit to drive a single DC motor with

feedback from a Hall-effect sensor is shown in Figure 10.

Pin D9 on the Arduino Nano is connected to ENA on the

driver board, D8 to IN1, and D7 to IN2. The Hall-effect

sensor output is connected to A5, which is used as a

digital input pin. Note that the jumpers must be removed

on the Enable pins ENA and ENB of the L298N module

to use PWM. These jumpers are shown in place on the

Fritzing diagram in Figure 10. Although an Arduino Nano

was chosen for the microcontroller, just about any other

microcontroller could be used.

A printed circuit board (PCB) was designed to fit an

ExpressPCB standard MiniBoard at 3.8 x 2.5 inches. This

circuit uses a single Nano to drive two of the L298N driver

boards (mounted vertically) and headers for eight 3144 Hall-

effect sensors. The layout for this board can be found in the

downloads. All the pins on the Nano are used, except for D0

and D1 which are used for the serial monitor.

The schematic for the linear actuator drive board is

shown in Figure 11.

Software

A program for multiple linear actuators to run on the

Figure 9. L298N motor driver module.

Figure 10. A circuit to operate a single motor with the L298N driver and Hall-effect sensors for feedback.

SERVO Issue-1.2020 51

Nano was created and

designed for use with

the circuit built on the

PCB. The program has

a few simple functions

to control four linear

actuators.

The functions

available are:

// Retract the actuator arm until it hits the home positionvoid homeMotor(int motor, int hall, int pwm)

// Soft start by increasing PWM before full powerbool softStartPWM(int motor, int setting, int maxPWM)

// Turn motor on, off, brake or free, turning at full powerbool setMotor(int motor, int setting)

// Turn motor on, off, brake or free turning using PWMbool setMotorPWM(int motor, int setting, int pwm)

// Read the output of a Hall Effect sensor, a low read means contactint readHall(int num)

// Run the motor for ¼ second so travel can be measuredvoid speedCheck()

The homeMotor() function is shown below and is

straightforward. It first checks if a correct motor has been

defined and if not, it returns with a false. Next, it turns

the motor on pulling the inner tube inwards, then begins

reading the Hall-effect sensor until it turns on. It then brakes

the motor and returns a true:

// Return motor to home positon, which is fully retractedbool homeMotor(int motor, int hall, int pwm){if ((motor != MOTOR_A) && (motor != MOTOR_B) && (motor != MOTOR_C) && (motor != MOTOR_D)) return

false; setMotorPWM(motor, MOTOR_IN, pwm); while (readHall(hall) == HALL_OFF) {}; setMotor(motor, MOTOR_BRAKED); return true;}

The setMotor() function is quite basic and is only

lengthy because it can service four motors. After doing an

error check for correct input, it uses a switch statement to

select which motor, then another switch statement to select

the setting:

// This function is used to turn a motor ON, OFF, BRAKED or OFF (free turning) at full powerbool setMotor(int motor, int setting){ if ((motor != MOTOR_A) && (motor != MOTOR_B) && (motor != MOTOR_C) && (motor != MOTOR_D)) return false; if ((setting != MOTOR_OFF) && (setting != MOTOR_BRAKED) && (setting != MOTOR_IN) &&

Figure 11. Design of linear actuator

drive board.

52 SERVO Issue-1.2020

(setting != MOTOR_OUT)) return false; switch (motor) { case MOTOR_A:switch (setting) { case MOTOR_OFF: digitalWrite(ENABLE_A, LOW); break; case MOTOR_BRAKED: digitalWrite(IN_A1, LOW); digitalWrite(IN_A2, LOW); digitalWrite(ENABLE_A, HIGH); break; case MOTOR_IN: digitalWrite(IN_A1, LOW); digitalWrite(IN_A2, HIGH); digitalWrite(ENABLE_A, HIGH);

break; case MOTOR_OUT: digitalWrite(IN_A1, HIGH); digitalWrite(IN_A2, LOW); digitalWrite(ENABLE_A, HIGH); break; } break; case MOTOR_B:switch (setting) { case MOTOR_OFF: digitalWrite(ENABLE_B, LOW); break; case MOTOR_BRAKED: digitalWrite(IN_B1, LOW); digitalWrite(IN_B2, LOW); digitalWrite(ENABLE_B, HIGH);

ITEM SOURCE

1/4-20 Threaded Rod Home Depot or Lowes

1/4-20 Nuts and Lock Washers, Stainless Steel Home Depot or Lowes

4-40 Flat Head Machine Screws and Nuts, 1/4, 3/8, and 5/8 lengths Home Depot or Lowes

4-40 Pan Head Machine Screws 1/2 inch, All Screws and Nuts Stainless Steel

48 Pitch Spur Gears Traxxas 2412, 2421, 2426, 2428, and 2431 Amazon or Local Hobby Shop

Hobbypark 48 Pitch Gear Set, 17, 21, 26, and 29 Teeth Amazon

Xnrtop 3 mm to 3 mm Shaft Coupling 25 mm length, 18 m diameter Amazon

8 x 3 mm Neodymium Disk Magnets Home Depot, Lowes, or Amazon

Loctite Marine Epoxy Amazon or Menards

White Lithium Grease Home Depot or Lowes

Johnson DC Motor, #G9332 Electronic Goldmine

L298N Motor Driver Board eBay or Amazon

Battery or Power Supply, 12 volt/3 amp Home Depot or Lowes

Arduino Nano eBay or Amazon

Hall-effect 3144 Sensors eBay

Printed Circuit Board or Breadboard ExpressPCB

Header Pins and Header Jumpers eBay or Amazon

Hookup Wire, Solder Home Depot or Lowes

Ball Bearing, 3/4 inch OD, 1/4 inch ID, 9/32 wide Amazon

If Printed Circuit Board is Built:

LM7805 Voltage Regulator eBay or Amazon

1,000 µF 6.3 volt Electrolytic Capacitor, .1 µF Capacitor eBay or Amazon

Tools Needed:

Small Lathe

3D Printer, Plastic Filament, Cuda Software, and Optional 3D Design

Software.

Parts List

SERVO Issue-1.2020 53

break; case MOTOR_IN: digitalWrite(IN_B1, LOW); digitalWrite(IN_B2, HIGH); digitalWrite(ENABLE_B, HIGH); break; case MOTOR_OUT: digitalWrite(IN_B1, HIGH); digitalWrite(IN_B2, LOW); digitalWrite(ENABLE_B, HIGH); break; } break; case MOTOR_C:switch (setting) { case MOTOR_OFF: digitalWrite(ENABLE_C, LOW); break; case MOTOR_BRAKED: digitalWrite(IN_C1, LOW); digitalWrite(IN_C2, LOW); digitalWrite(ENABLE_C, HIGH); break; case MOTOR_IN: digitalWrite(IN_C1, LOW); digitalWrite(IN_C2, HIGH); digitalWrite(ENABLE_C, HIGH); break; case MOTOR_OUT: digitalWrite(IN_C1, HIGH); digitalWrite(IN_C2, LOW); digitalWrite(ENABLE_C, HIGH); break; } break; case MOTOR_D:switch (setting) { case MOTOR_OFF: digitalWrite(ENABLE_D, LOW); break; case MOTOR_BRAKED: digitalWrite(IN_D1, LOW); digitalWrite(IN_D2, LOW); digitalWrite(ENABLE_D, HIGH); break; case MOTOR_IN: digitalWrite(IN_D1, LOW); digitalWrite(IN_D2, HIGH); digitalWrite(ENABLE_D, HIGH); break; case MOTOR_OUT: digitalWrite(IN_D1, HIGH); digitalWrite(IN_D2, LOW); digitalWrite(ENABLE_D, HIGH); break; }

break; } return true;}

This program doesn’t need to be run with the included

PCB design. Point-to-point wiring can be used between

the Nano, Hall-effect sensor, driver board, and motor. By

following the pin assignments in the program shown below,

it can be used as a general interface for one to four linear

actuators.

Pin assignments can also be changed in the program to

suit user needs.

#define HALL1 A5#define HALL2 A4#define HALL3 2#define HALL4 4#define HALL5 12#define HALL6 13#define HALL7 A7#define HALL8 A6#define ENABLE_A 9#define IN_A1 8#define IN_A2 7#define ENABLE_B 3#define IN_B1 6#define IN_B2 5#define ENABLE_C 11#define IN_C1 A0#define IN_C2 A1#define ENABLE_D 10#define IN_D1 A2#define IN_D2 A3

A copy of this program is included in the downloads.

Conclusion

This was an enjoyable project, even though many hours

were spent getting things “just right.” For the builder, it’s

imperative that everything runs smoothly with little friction.

It’s worth the extra effort to reprint something (like the inner

tube) if it sticks slightly when moving in and out. With the

small motor used, it doesn’t take much friction to bind and

stall the motor.

When the threaded rod and its bearing are inserted into

the main body, be sure everything can turn easily using a

thumb on the gears or coupling. A small amount of white

lithium grease can be used on the gears and threaded rod

to reduce friction. The pillow block that holds the bearing in

place should fit snugly, but do not overtighten it.

Using 3D printing allows for custom attachment

methods, depending on the use intended for the linear

actuator. My models simply have a mounting hole at each

end, but a simple redesign would allow a better integration

into the model the linear actuator moves. SV

54 SERVO Issue-1.2020

Versatile Stepper Control By William Cooke

SERVO Issue-1.2020 55

I’m going to borrow a method often used for generating radio and

audio signals and use it to generate step rates for motors. We’ll

be able to step several motors, with each motor having individual

control of the step rate and number of steps.

The code uses interrupts and runs mostly in the background, allowing

your controller to continue doing whatever else it needs while the steppers

continue stepping along. The example uses an Arduino, but you can apply it

to almost any controller.

Brief Review of Steppers

Let’s take a brief review of how to control a stepper. We’ll only cover the

parts relevant to us, so if you want to know more about steppers, check out

the References.

For control purposes, there are two basic types of steppers: bipolar and

unipolar. Refer to Figure 1. A unipolar motor appears to the control circuits as

(usually) four motor windings.

Those four windings are connected together at one end, either internally

or externally to the motor. That mutual connection is attached to one side of

the power supply, most often the positive side. By connecting the other end

of the winding to the other side of the supply, our circuit can energize that

winding. We only control one side of the supply. Hence, the name “unipolar.”

A bipolar motor, however, usually has two windings. We control both

Stepper motors are a staple of robotics. They’re great for precise

speed and positioning. It’s also easy to control one. But what about

two, or three? With different step rates? For different amounts of

time? While your microcontroller continues doing other tasks? It can

quickly become difficult, but with the technique presented here you

can do all that and use only about two or

three percent of the microcontroller’s time.

Figure 1. Schematic diagram of unipolar and bipolar stepper motors with

representative driver circuits. The circuits are incomplete and only used for

reference.

56 SERVO Issue-1.2020

ends of both windings. Our control circuit (using an H-bridge

or something similar) can connect either end to either side

of the power supply.

If we connect one end to positive and the other to

ground, current will flow in one direction. If we reverse both

ends, current flows in the other direction. If both ends are

connected to the same side of the supply, no current flows.

So, now we can energize the winding in either direction or

not at all. That’s why these are called “bipolar.”

It would seem the control of these two types of motors

would be very different. However, it turns out our software

can control them exactly the same. Both types have four

connections. The unipolar has connections to one end of

four windings. The bipolar has connections to two ends of

two windings. In both cases, if we energize the windings in

the correct sequence, the motor will step.

A single output bit can either energize or not energize

a winding in a unipolar motor. In a bipolar motor, two bits

together determine if a winding is energized and in which

direction. A sequence of patterns applied to either motor

makes it go around. Reversing the sequence makes it spin

the other direction. It turns out that both motors use the

same patterns and sequences.

There are three common sequences of patterns: full-

wave, half-wave, and half-step. The full-wave and half-wave

take a complete step with each pattern change. The half-

step takes half a step (as expected) for a total of twice as

many steps. Look at Figure 2 for all three patterns and how

they apply to both types of motors.

The full-wave sequence energizes two windings at once

and gives the most torque. It also uses the most energy.

The half-wave sequence only energizes one winding at a

time. Although it also takes full steps, the steps are halfway

between those of the full-wave sequence. Since only one

winding is energized, it has less torque but uses less power.

The half-step sequence is a combination of the two

previous sequences. It takes twice as many patterns but

gives twice as many steps. It also gives torque between the

other two. The driver electronics may

be as simple as four transistors for

a unipolar motor. H-Bridge chips are

typically used for bipolar motors, but a

DPDT relay is also effective.

In the example system shown,

I used a ULN2803A (with eight

Darlington pair transistors) for two

unipolar motors and a SN754410 dual

H-bridge to control one bipolar motor.

To control the motor, we send

the bit pattern to the winding drive

electronics. Stepping through the table of bit patterns —

either forward or backward — steps the motor forward or

backward, respectively. When we reach one end of the

table, we wrap around to the other and continue on.

Controlling One Motor

Once we decide to use a stepper, we may want to step

some number of steps per second for a certain number of

steps. After a bit of thinking, we dive in and write some

Arduino code. Maybe it looks like this:

uint8_t fullWaveTable[] = { 0x03, 0x06, 0xc0, 0x09 }; // Full Wave table 0011, 0110, 1100, 1001

void stepMotor(uint16_t steps, uint8_t delayTime){ for(uint16_t step = 0; step < steps; step++) { uint8_t outputValue = fullWaveTable[step % 4]; sendToMotor(outputValue); // Send this bit pattern to controller delay(delayTime); }}

That will work. It will step a motor up to 65,535 steps

with a delay between steps of 0 to 255 milliseconds.

Unfortunately, it has problems.

Perhaps the most obvious problem is that the Arduino

can’t do anything else while the motor is running. If we

ask it to step the motor 10,000 steps with a delay of 20

milliseconds (50 steps per second), our Arduino will be

tied up doing nothing else for 10,000 * 20 = 200,000

milliseconds. Over three minutes.

A bit less obvious is what if we want a step rate of 750

steps per second? A delay value of 1 gives about 1,000 steps

per second and a value of 2 gives 500 steps per second.

We could use something like delayMicroseconds() and that

might fix the timing problem, but it doesn’t help with the

other issues. Plus, it adds plenty of problems of its own. We

Figure 2. Full-wave, half-wave, and half-

step stepping patterns for unipolar and

bipolar motors. The table entries for

the windings match those in Figure 1.

SERVO Issue-1.2020 57

won’t pursue that any further.

Here’s another problem. Suddenly, we remember the

robotic arm we’re building needs three motors moving

simultaneously but at different rates, and may not start and

stop at the same time.

I encourage you to try to extend the function above

to handle two motors with different numbers of steps and

different stepping rates. If you manage to make two work,

try three.

A Better Way

We can take a big step forward by using interrupts.

An interrupt is like a phone ringing. You can be working

on something and paying no attention to your phone, but

when it rings, you stop what you’re doing and handle the

call. When complete, you start back right where you left off.

An interrupt in a microprocessor is like a telephone ring.

The processor pays no attention to some

device until an interrupt is activated; it

stops what it’s doing and saves enough

information to come back later. It does

whatever is needed by the interrupt and

goes back to what it was working on.

If we have some device interrupt

the processor at regular intervals, we

can handle the stepper motor(s) without

using any delays. Instead of spinning our

wheels waiting on time to pass, we do

other tasks that need to be done.

For example, if we have a hardware

timer interrupt the processor 1,000

times per second, we can step our motor

each time. If we want it to step slower,

we can step every second or third or

whatever time. That solves the problem

of the controller spending all its time

waiting. It also makes it fairly simple to

control more than one motor. We still

have the issue of resolution; we can have

1,000 steps per second or 500 steps per

second, but not 750 or 800.

Interrupts are a huge topic by

themselves. It’s important to keep the

Interrupt Service Routine (ISR) short and

fast. It’s also important to protect any

data that may be accessed by both the

interrupt and the main code.

Often, that means turning off

interrupts in the main code before

accessing that data and turning them

back on after. You can see examples

in the project we’ll be discussing, plus

Reference 2 has some good basic

information.

Fractional Steps

What if we could take an arbitrary fraction of a step?

Say, 4/5 (0.8) or 3/4 (0.75)? With 1,000 interrupts per

second and taking 4/5 steps per interrupt, we could have

800 steps per second. Or, 3/4 would give us 750 steps per

second. It turns out we can.

Radio and audio frequency signal generators, arbitrary

waveform generators, “wavetable” sound systems, and

various other types of signal generating systems use a

technique called Direct Digital Synthesis (DDS). We can

borrow DDS to generate our stepper waveforms.

DDS is a fascinating technique and I encourage you to

check the References to learn more about it. Let’s apply it

to making things spin!

Instead of an audio or radio signal, our waveform is the

pattern sequence we chose to drive our stepper. By taking

fractional steps at each interrupt, we can get almost any

desired step rate up to the maximum,

which is the interrupt rate.

The trick is a variable called a “phase

accumulator.” The variable is broken into

two parts: two or three bits are used to

index into our pattern sequence table;

the rest represent a fraction.

As an example, let’s create a five-bit

phase accumulator and use the full-wave

table. For either the full-wave or half-

wave tables, we use the most significant

two bits, and for the half step table, the

upper three bits. Refer to Figure 3.

When our interrupt calls, we add a

number to the phase accumulator. Then,

we take the most significant two bits

to index into the step table. We output

the value at that location to the motor

controller.

Those extra three bits represent

a fraction. Three bits represent eight

different numbers from zero to seven, or

1/8 of a step. Adding one to the phase

accumulator each time effectively takes

1/8 of a step. If we add four each time,

we take a half step (4/8). Adding eight

each time will take a full step, which is

the max.

In Figure 3, the entries highlighted

in yellow represent the steps taken with

a five-bit phase accumulator, a four-entry

table, and an increment of five.

You can see some numbers are

output more than once, but that has no

effect on the result. The motor won’t

care if you re-write the same value to it.

Increments can be any value from

Figure 3. An example five-bit phase

accumulator showing how steps are

taken with an increment of five. The

individual patterns are color-coded on

the right and the phase accumulator

values are highlighted in yellow.

58 SERVO Issue-1.2020

zero (motor stopped) to eight (one step per interrupt.) Our

step rate can be 1,000 * n/8: 0, 125, 250, 375, 500, 625,

750, 875, and 1,000. If we increase the size of the phase

accumulator, that leaves more bits for the fraction. A good

size is 16 bits.

With a four-

entry table, 14

bits are left for the

fraction, giving

a step resolution

of 1/(2^14),

or 1/16384

(0.000061) step.

Again, at 1,000

steps per second,

we get 1,000 *

n/16384 steps per

second.

Here is the

general formula:

StepsPerSecond

= InterruptRate

* Increment /

(2^FractionBits)

We rearrange

that to be more

useful and find the

needed increment:

StepRate =

InterruptRate *

n/16384

rearranging:

n = StepRate * 16384 / InterruptRate

To find n for 750 steps per second:

n = 750 * 16384 / 1000 = 12,288

or for 800:

n = 800 * 16384 / 1000 = 13,107.2.

Round down to 13,107 for

799.99 steps per second — probably

close enough. If you really need

better resolution, you can go to a

32-bit phase accumulator, but that

isn’t often necessary.

What if we want to go really

slow?

Photo 1. The example prototype

board with one unipolar and one

bipolar motor attached.

Figure 4. Schematic diagram of the

example system showing the Arduino

Nano, the ULN2803 used to drive two

unipolar motors, and an SN754410

used to drive a single bipolar motor.

SERVO Issue-1.2020 59

n = 0.1 * 16,384 / 1,000

n = 1.64 round to 2

StepRate = 1,000 * 2 / 16384 = .122 steps per second

Remember that you can never take a step larger than

1.00 or the motor will miss steps. That means for a 16-bit

phase accumulator and two-bit index, the maximum value is

16,384. For a three-bit index, it’s 8,192. In either case, we

get one step every interrupt.

Note how simple it is to take a step and calculate the

next one:

1. Use the upper bits of phase accumulator to index

table.

2. Output table value to motor driver.

3. Add increment to phase accumulator, rolling over

at either end.

That’s it! Simple and fast. Note that the increment can

be negative, which steps backward.

Example Implementation

I promised an Arduino example. Let’s use an Arduino

Nano, two unipolar motors, and one bipolar motor. We will

use the half-wave step table. It should be relatively simple to

change how many and the types of motors or the step table

used if you stay with an Arduino.

Moving to a different controller will be more work;

you’ll need to know what timer, interrupt, and input/output

resources are available. The schematic is shown in Figure

4. The complete source code (Listing 1) is available in the

downloads.

Getting the Interrupts

First, we need a source of interrupts. Most stepper

control applications will be well-served with an interrupt

rate of around 1,000 interrupts per second. That will allow

almost any rate up to the interrupt rate. For a stepper with

200 steps per revolution, we get five revolutions per second

or 300 RPM.

The Arduino has a timer that interrupts close to 1,000

times per second for the millis() counter. Timer 0 on the AVR

chip (the chipset used by most Arduinos) counts from 0 to

255 and interrupts when it rolls over to zero. Actually, 997

times per second; close enough. The only problem is we

can’t hijack that interrupt. But we can hitch a ride!

Timer 0 also has two compare registers not normally

used that can interrupt when their value matches the

counter. Let’s use one.

To avoid the interference to the millis() interrupt, we

set the compare register to a value other than zero. A good

choice is 0x20 (32 decimal); about 1/8 millisecond after the

rollover interrupt. Plenty of time for the millis() counter to

finish. It’s simple to do. We write the value to the compare

register, then enable the interrupt. We do that in the setup()

function. Here’s the required code:

// Set up the Compare A Register timer interrupt OCR0A = 0x20; // Set the compare A register to 0x20, away from 0 TIMSK0 |= 2; // enable the compare A interrupt

Processing the Interrupt

When the interrupt occurs, the ISR is called. It looks

much like any normal function, but there are some

differences. First, a special syntax is used to create it.

Second, it must not have any inputs or return a value.

Interrupt routines should be short and fast. They should

only do the minimum amount of processing required.

Anything that can be done outside the ISR should be.

Interrupt programming can be full of headaches, but if

you’re careful, it isn’t too bad. I strongly encourage you to

read up on the subject.

The ISR is the heart of this method. The demo is for an

Arduino, but most of the code is generic and should work

unchanged or with small changes on most processors. The

code in the listing is heavily commented, so I won’t discuss

most of it, but let’s take a look at the ISR.

First, there are several variables that technically

aren’t part of the ISR but are critical to its operation. The

first — stepper_phase — is an array that holds the phase

accumulator for each motor.

The second is another array — stepper_stepSize —

that holds the phase increment for each motor. Next is

stepper_steps, holding the number of steps for each motor

to take. The last is a single variable called stepper_running

to indicate if any motors are currently running.

Here’s the first half of the ISR. The part not shown is the

output to the motors. You can see it in the main listing, but

you’ll likely need to change it to match your hardware.

ISR(TIMER0_COMPA_vect){ static uint16_t oldIndex[NUM_MOTORS]; // store old index to test if we step

if(stepper_running) { uint16_t index; uint8_t out[NUM_MOTORS];

for(int mtr = 0; mtr < NUM_MOTORS; mtr++) { if(stepper_steps[mtr] != 0) { stepper_phase[mtr] += (uint16_t)stepper_stepSize[mtr]; index = stepper_phase[mtr] >> stepper_indexShift; out[mtr] = stepper_stepTable[index]; if(index != oldIndex[mtr]) { stepper_steps[mtr]--;

60 SERVO Issue-1.2020

oldIndex[mtr] = index; } } }

// Code to output to motors goes here

}}

The first line of the ISR is how we declare an ISR for

the Arduino compiler. It looks like a function named “ISR”

with the name of the interrupt in parentheses. For any

Arduino based on the AVR chips, you can get the interrupt

name from Reference 4. If you’re using some other type of

controller, you’ll need to find out how to use an appropriate

interrupt.

You’ll have to research that on your own. Interrupt

control is not a standard part of the C or C++ languages, so

every compiler does it differently. Even the same compiler

may be different on different processors.

Inside the ISR, we first declare an array named oldIndex

to hold all the previous index values, so we can determine if

a motor stepped in this iteration. By declaring the array as

“static,” it holds its values between calls to the ISR. Another

array named out temporarily holds the table values to write

to the motors.

The main body of the ISR is a for loop that cycles

through all the motors. First, it checks if the motors are

running and skips everything else if not. If the motors are

running, it adds the phase increment for each motor to the

corresponding phase accumulator.

The resulting phase is used to find the index and look

up the needed pattern from the pattern table, stepper_

stepTable. It saves that pattern to use later.

The new output values found for the motors are

compared to the previous values held in the oldIndex array.

If they’re different, it means that motor took a step, so the

step count is updated. The only thing left to do is write the

new table values out to the motor controllers.

The ISR is short and simple. All the supporting code and

interface functions are in Listing 1.

In the example, I used direct port I/O. I highly

recommend doing that. Using the digitalWrite function is

slow and can cause performance issues with your code as

well as the motors. Reference 6 has information on using

direct port I/O.

In all, the example controls three motors and uses only

about 2% of the processor’s time, leaving plenty for your

other code.

Conclusion

You can take the example project here and use it

immediately to control three motors. Of course, much more

can be done by using it as a basis for your own ideas.

I hope you’ll take the techniques presented and go

further. Interrupts are a powerful tool and most processors

have many interrupt sources.

The phase accumulator/DDS method presented here is

useful for creating many different types of repetitive actions

that don’t match timer interrupt rates. I look forward to

hearing what you create and perhaps reading about it in

these pages.

As a final note, I’d like to thank my friend, Thomas

for asking the question that led to this article, and then

encouraging me and reviewing it. SV

1. Douglas W. Jones on Stepping Motors http://homepage.divms.uiowa.edu/~jones/step/ More than you ever wanted to know about steppers. 2. Arduino attachInterrpt() Reference https://www.arduino.cc/reference/en/language/functions/external-interrupts/attachinterrupt 3. DS Tutorial https://www.analog.com/en/analog-dialogue/articles/all-about-direct-digital-synthesis.html#Ask The Application Engineer—33: All About Direct Digital Synthesis by Eva Murphy and Colm, Slattery. A great introduction to Direct Digital Synthesis.

4. Interrupt Names AVR LIBC Interrupts https://www.nongnu.org/avr-libc/user-manual/group__avr__interrupts.html Lists the interrupt names recognized by the GCC compiler for all supported AVR processors. 5. Wikipedia entry on Direct Digital Synthesis https://en.wikipedia.org/wiki/Direct_digital_synthesis More good information on DDS. 6. Direct Port I/O on Arduino https://www.arduino.cc/en/Reference/PortManipulation Explains how to use direct port I/O instead of the Arduino single pin method.

References / Further Reading

To post comments on this

article and find any associated

files and/or downloads, go to

www.servomagazine.com/

magazine/issue/2020/01.

SERVO Issue-1.2020 61

LASER ALIGNMENT LASER ALIGNMENT

SYSTEM FOR SYSTEM FOR

YOUR CNC YOUR CNC

ROUTERROUTER

By Roger D. Secura

I really like simple solutions to

problems. For example, I designed and

built a desktop CNC router some time

ago. Although it works as expected,

I was wasting a lot of time trying to

align the center of my tool bit with the

corner edge of my workpiece (wood).

Then, like a fl ash of light (no pun

intended), it hit me — use a laser to

fi nd the edges of the wood. As it turns

out, designing and building a laser

system for my CNC router was really

simple — just what I like.

62 SERVO Issue-1.2020

WHAT TO EXPECTIn this article, I’ll show you how to build a laser power

supply circuit and how to construct a special bracket for your

CNC router motor. Figure 1 shows the kind of output you

can expect from my laser system.

You’re going to like the fact that the power supply

circuit only requires three components: the LM317T voltage

regulator and two resistors. If that sounds good to you, keep

reading.

START WITH THE BRACKET

Figure 2 is the CAD drawing for the bracket that holds

the two lasers in place. Figure 3 is a photo of the bracket

after it was printed on my Alfawise U30 3D printer. Finally,

Figure 4 shows the bracket mounted onto the CNC router

motor.

Aligning and mounting the bracket is really simple. Draw

(pencil) a temporary 90° angle on your router table so that

each leg of the 90° angle is an equal distance from the edge

of your table. Place a board in the corner of the angle. Now,

slide the bracket onto the motor and lightly tighten the #6-

32 machine screw. Rotate the two “line” lasers so they align

themselves with the lower left-hand corner of the board

as shown in Figure 1. Once aligned, level and tighten the

bracket around the motor.

Now, using the two laser lines as a guide, it’s possible

to center a router bit to any X and Y location on your table.

For example, move your cutting tool to the Home position

(Machine Zero). In the Offset screen in Mach 3, enter: X = 4;

Y = 4. Now, hit the ‘Go to Zero’ button on the main screen

in Mach 3. Once you reach the designation X = 4 / Y = 4,

the lasers will show you where to put the corner of your

workpiece.

Please note that this bracket was designed for my

DeWalt DNP611 router. You may

need to adjust the inner diameter

(2.75”; see Figure 2) of the

wooden bracket to fit your router

or spindle motor. Be aware that

in some cases, this bracket may

interfere with the movement and/

or travel limits of your Z axis.

Also, since both lasers have

a focus adjustment screw on the

front lens, you should unscrew the

lens and add some Teflon tape

(plumber’s tape) around the screw

threads.

Apparently, the screw is too

loose (bad design/manufacturing)

to maintain a set focus point.

Watch out for the spring inside the

laser. It will pop out.

Finally, once you insert the

9/64” diameter mounting screws

into the bracket, don’t over-tighten

FIGURE 1

FIGURE 2

SERVO Issue-1.2020 63

the screws. You could crack the bracket or the laser.

OKAY, LET’S POWER UP THE LASERS

As you can see in Figure 5, the circuitry required

to power the lasers is quite simple. I wanted to use 9V

batteries, so I wouldn’t have to keep replacing them so often

(like I would with AA batteries).

This requirement forced me to find a voltage regulator

that could step down the voltage from nine volts to 3.3 volts

— the laser’s operating voltage. Fortunately, the LM317T

met my requirement and did so with just a couple of extra

components — two resistors!

You’ll need to build two of these circuits; one for each

laser. Get some general-purpose PC board (2-7/8” L x 1-7/8”

W) and hard-wire the components as shown in Figure 6.

You can glue or Velcro™ the battery clips to the

perfboard. This makes it easy to replace the 9V batteries

when they get low. Figure 7 shows the circuit board

mounted onto the CNC machine.

HOW THE CIRCUIT WORKS

The LM317T voltage regulator is kind of

amazing for what it can do. If you insert a

potentiometer into the circuit (R2), you can

vary the regulator’s output voltage (Vout) from

1.25V to 37V.

The uniqueness of the LM317T is that

you only need to add two resistors to get any

output voltage between 1.25V and 37V.

According to the datasheet, the LM317T

must have a minimum of 10 mA flowing

through resistor R1 or it falls out of regulation.

In addition, by design, the regulator will

always have a constant “reference” voltage level

of 1.25V across R1, measured from pin 2 to pin

1. In order to determine the resistor value for

FIGURE 3

FIGURE 5

FIGURE 4

64 SERVO Issue-1.2020

R1, we use Ohm’s Law as follows:

R1 = E/I

R1 = 1.25V/10 mA

R1 = 125 ohms

As you can see, the value for R1 is 125 ohms. Let’s

verify the minimum required current running through R1 is

10 mA:

IR1 = E/R

IR1 = 1.25V/125 ohms

IR1 = 10 mA

Since the current running through R1 is 10 mA, the

series circuit of R1 and R2 dictates that the same 10 mA

must run through R2. To calculate the resistance value for

R2, we use the following formula (use 3.3V as our desired

output voltage for the laser):

R2 = 205 ohms

Now, insert R1 (125 ohms) and R2 (205 ohms) into the

circuit. Take a voltmeter and check the output voltage and

verify that it’s 3.3V, measured from the Vout terminal to

ground.

Notice that if we add the 1.25V across R1 and the

2.05V across R2, we get 3.3V at the Vout terminal. In other

words, since the voltage across R1 (1.25V) never changes,

we can control the output voltage at the Vout terminal

(1.25V to 37V) just by varying the resistance of R2.

If you’d rather not do the math, you can just make R1

equal to 125 ohms and use a potentiometer for R2. Now,

turn the pot (R2) until the desired output voltage (measured

from Vout to ground) is acquired.

Remove the pot from your breadboard and check

the ohm’s setting with an ohmmeter. Insert an equivalent

resistor value back into the circuit.

Again, check the voltage level at the Vout terminal to

verify that you have the required output voltage; 3.3 volts

for example. Done!

Okay, now for a few caveats about the LM317T. First,

the input supply voltage at pin 3 (Vin) MUST be a minimum

of 2.5V to 3V higher than the output voltage (Vout). In

other words, if you need 3.3V for Vout (load), Vin must be

at least 6.3V. Failure to adhere to this rule will cause the

LM317T to fall out of regulation.

The ‘minimum’ differential voltage between Vin and

FIGURE 6

FIGURE 7

SERVO Issue-1.2020 65

Vout is called the “drop-out”

voltage (see the datasheet). If you

go below the minimum (3V), the

regulator stops working.

Secondly, the larger the

voltage differential is between Vin

and Vout, the more heat will be

dissipated within the LM317T. It

makes sense.

If, for example, you have

a 12V supply coming into the

regulator at pin 3 (Vin) and your

Vout (load voltage) only requires

3.3V, the LM317T will have to

dissipate the voltage differential

(5.7V) as heat.

As a rule of thumb, the larger

the differential, the more heat is

generated. This means a heatsink

may be required.

LASERSThe two lasers used in this project (and shown in Figure

8) are called “line” lasers. In other words, you can buy lasers

that project a single line, a cross pattern, or a dotted line

pattern. Just be careful when buying your lasers online. Look

for focusable 5 mW line lasers.

WARNING! WEAR EYE PROTECTION!

No project is worth damaging your eyesight. Any

time you work with lasers, you need eye protection. Just

remember, a laser beam reflected

off a shiny surface could accidently

target your eyes.

Please, don’t power-up your

5 mW lasers until you have read

‘Sam’s Laser FAQ’ at www.

repairfaq.org/sam/lasersaf.htm.

The 5 mW lasers used in this

article have a wavelength of 650

nm-660 nm. Therefore, before you

buy a pair of safety goggles, drop

by YouTube’s website and enter

the following text into the Search

Box: “Choosing Laser Goggles”

and “Testing Laser Goggles.” Don’t

buy those cheap goggles and

damage your eyesight!

Spend the extra money and

get a good pair of safety glasses.

You’re worth it! SV

To post comments on this article and find

any associated files and/or downloads, go to

www.servomagazine.com/magazine/issue/2020/01.

FIGURE 8

PARTS LIST

ITEM QTY DESCRIPTION PART# SOURCE

R1 1 125 ohm, 1/4W, 1%, Metal Film 71-RM60D1250F Mouser

R2 1 205 ohm, 1/4W, 1%, Metal Film 71-CMF50205R00FHEB Mouser

IC 1 Voltage Regulator, 1.25V-37V 511-LM317T Mouser

Laser 2 650 nm, 5 mW, Red, Focusable, “Line” Laser with Driver, Working Voltage 3-5V, Dimensions 12 x 35 mm

650ML-5-1235-2pcs-LM Amazon

Goggles 2 Red, 635-660 nm Laser Protection NYBG Amazon

Perf Brd 1 General-Purpose Grid-Style PC Board 276-150 RadioShack

Screw 3 Machine, #6-32 x 1-3/4”, Phillips n/a Home Depot

Nut 3 #6-32 Machine Screw Nut n/a Home Depot

Washer 3 #6 Lock Washer n/a Home Depot

Battery 2 9 VDC n/a (optional)

Bat Snaps 2 9 VDC Battery Snaps & Contacts 121-0526/I-GR Mouser

Bat Clip 2 9V Horizontal Battery Clip 12BH071-GR Mouser

66 SERVO Issue-1.2020

As I moved forward to do my Masters in Advanced

Manufacturing, I had a course on industrial robotics.

While doing that class, our professor came up with

an idea that a simple two-link robot could be used to

write letters. Figure 1 shows the simple two-link robotic arm.

It’s called a 2R robotic arm since it has two revolute

joints connecting two links. At the end of the robot, there’s

an end effector which, in our case, is a pen to write the

letters.

In this DIY project, I’ll show you how to make a simple

computer-controlled letter writing robot from scratch. Once

you have all the required materials, it will take about an hour

to complete the build. The robot arm writes a designated

letter on a piece of paper when a particular button is

pressed on the screen that’s part of the build. You can see

what it’s writing in the camera using the Graphical User

Interface (GUI).

You can see the robot arm in action at https://youtu.

be/-GWMAvIMX4w.

Make Sure You Have These to Begin

First, we’ll be making the two-link robotic arm.

For this, we’ll need two servomotors with at least 10-

15 kg cm torque for better results. You can also use

9g servo motors.

Next, is two 30 centimeter wooden or steel rulers

to make the links of the robotic arm.

A drill and a few nuts and bolts are necessary to

fit the wooden or steel ruler to the servo horn. An

L clamp or a piece of sheet metal that can be bent

into an “L” shape is needed to hold the pen or pencil

using a paper clip.

A few male-to male jumper wires are needed

to connect the servomotors to the microcontroller.

An Arduino Uno with a USB-UART cable is the

microcontroller I used. A 5V 1A power supply is

required to power the servomotor.

Alpha-Writer:Back from my school days, I remember my teachers

giving homework that involved a lot of writing. I

always wondered why there couldn’t be a robot that

would do this task of writing homework for me. I’m

glad it’s now possible to make this happen.

FIGURE 1: Representation

of a simple two-link robotic

arm with joints and end

effector.

SERVO Issue-1.2020 67

Building the Two-Link Robotic Arm

Find a big pad or a table and fix one of the

servomotors to it. Attach the ruler to the servo

horn using the nuts and bolts. Attach the second

servomotor to the other end of the ruler. Your setup

should look something like Figure 1. You’ll now need

to make a similar horn and ruler setup as shown in

Figure 2.

Next, attach the L clamp to the

end of the ruler so that the pen or

pencil can be attached to it. Refer to

A Computer-Controlled Letter Writing Robotic Arm

FIGURE 2: The first servomotor is attached to ground. The ruler is connected to the horn. The second servomotor is attached to the other end.

FIGURE 3: The second link of the robotic arm is made by attaching to the horn of servomotor 2.

By V S Rajashekhar

Try changing the initial angle of the

mechanical robotic arms and you’ll

find differences in the font style!

68 SERVO Issue-1.2020

Figure 3. Attach the servo horn with the ruler and pen to

the second servomotor. Your two-link robotic arm is ready

and should resemble Figure 4.

Circuit ConnectionsThe circuit is shown in Figure 5. A breadboard

is used and the 5V 1A power is attached to it. From

this, the power is distributed to the two servomotors.

Pins 10 and 9 are given to the servomotor as 1 and 2,

respectively.

Here, servomotor 1 is the grounded motor and

servomotor 2 is the motor that is attached to the link

connected to servomotor 1.

Finally, connect the male-to-male jumper wire from

the ground pin of the Uno to the ground in the

breadboard.

Software Setup and Running the Code

A. Programming the Microcontroller

Open your computer and install the Arduino

software. You can get it from https://www.

arduino.cc/en/Main/Software.

Open the Arduino file that is included with the

downloads for this article. Connect the Uno to the

computer and upload the code. Remember to keep

the board connected to the computer until the end of

the project.

The following block of code tells you that the

letter A will be written if the button A is pressed in

the GUI (covered next):

FIGURE 6: The circuit diagram of the robotic arm with the

motors and microcontroller.

FIGURE 4:

The color pen

attached to

the L clamp

made of

sheet metal.

This is the

end effector.

FIGURE 5: The assembled robotic arm ready to

write the letters.

SERVO Issue-1.2020 69

if(val == ‘a’){ //if a received myservo1.write(0); myservo2.write(15); delay(2000); . . . myservo1.write(0); myservo2.write(22.5); delay(2000); }

If button A is pressed, that

value is sent to the microcontroller.

It makes servomotor 1 (myservo1)

and servomotor 2 (myservo2) move

to certain angles with a delay of two

seconds in between each transition.

B. Graphical User Interface

1. Download the Processing

software at https://

processing.org/download.

2. Open the fi le alpha_writer.pde

that’s in the article downloads.

3. Look out for this line: port

= new Serial(this, “/dev/

ttyACM0”, 9600);

Replace “/dev/ttyACM0” with

the port name to which your

Arduino is connected. Don’t forget

to use the double quotes.

4. Run the Processing program and

you should get the screen shown

in Figure 6.

Success! You’re ready to write

letters by clicking on the button shown

in the screen.

Adjust a camera (possibly a web

camera) over the robot so that you can

see what it’s writing.

Watch the computer-controlled

robotic arm writing all 26

English letters at https://youtu.

be/0612D6gnf3U. By adjusting

the initial position of the links, the robotic arm writes in

a different font as shown at https://youtu.be/5QB-

lQINRKw.

I hope you fi nd this “write” on the money for your next

computer-controlled project! SV

www.melabs.com

� Everything you need to learn to program PIC® micro-

controllers is included in this package

� Learn the fundamental concepts of programming,

including program flow, loops, coding techniques, binary

manipulation, device-to-device communication, user

interface design, in-circuit debugging, and more!

� Includes all the necessary the software, compiler,

trainer board, cable, tutorial with exercises and sample

code!

THE MOST COMPLETE PROGRAMMING TUTORIAL!

$99.99Academic and bulk pricing available

Check out our other popular products

for PIC® developers including:

U2 Programmer

PBP3 Compiler

Prototyping Boards

Experimenter Boards

Contact us at info@melabs.com

PICBASIC PRO™ Compiler

PBP3

FIGURE 7: A GUI used for giving the input to the robotic arm.

The more rigid the robot

is, the more accurate the

letters written will be!

To post comments on this article and fi ndany associated fi les and/or downloads, go to

www.servomagazine.com/magazine/issue/2020/01.

70 SERVO Issue-1.2020

We yearn for the best return on investment

when it comes to selecting a car. Our go-

to parameters to shortlist cars have been

consistent over the years. A standard question

which is still very valid today is, “Mileage kitna deti hai?” or

what is the mileage?

This continues to be a major deal breaker for a good

portion of customers, but most buyers also consider the

size of the vehicle, expected resale value, fuel cost, and

after-market service. As of late, buyers have also started

considering the safety features (airbags, ABS). This was a

result of lenient regulations on the safety requirements.

Early adopters have added another new and very

critical parameter to this checklist, which is whether the car

has in-built connectivity. To understand the importance of

these features, the late adopters need to catch up with this

innovative suite of connected car services or else they will

miss out on a very exciting — yet important — experience.

There’s a saying that the cars we drive say a lot about us. I think this

couldn’t be more true in the world we live in.

Connected Cars — A Fast Brewing World

in Automotive

Somewhere in a Utopian world where each car communicates with one another. After

all, communication is the key to staying connected.

SERVO Issue-1.2020 71

By Abhinav KumarTo post comments on this article, go to www.servomagazine.com/magazine/issue/2020/01.

If the buzz phrase “connected car” caught your

attention, read on.

Let’s begin by answering what a connected car is all

about.

A connected car is a vehicle which has the ability to

communicate with systems both inside and outside, using in-

car connectivity. A connected car has Internet access within

it which allows data sharing with devices (also) both inside

and outside the vehicle.

In more basic terms, you’re driving a vehicle which is

constantly sending key data points from the car to a cloud-

based application hosted at a secure site. Now, please don’t

jump to the conclusion of your privacy being compromised

which is not the case here, but surely one should have

concerns. However, that’s a discussion for another day which

will last for years to come.

Next, you want to inquire about the services which are

enabled in a connected car.

Typically, the following are the broad services which can

be activated using the connected car suite:

1. Car Navigation: The features under this category

allow the driver to make informed decisions on reaching a

destination quickly, safely, and in a cost-effi cient manner

using navigation data (current traffi c information, shortest

routes available, and parking lot or garage assistance,

eventually leading to optimized fuel consumption).

2. E-commerce: This could be an array of services

enabling users to purchase goods or services on-the-fl y. (Pay

for your fuel from your car app, order food and beverages,

pay parking, tolls, etc.)

3. Vehicle Insights: These functions enable drivers to

know the vehicle condition and further help them reduce

operating costs and improve ease of use (vehicle condition

— mainly referred to as telematics — and service scheduling

and reminders based on the vehicle condition, remote

operations, etc.).

4. Breakdown Prevention: This is basically predictive

analytics or data to analyze to predict events. In this, using

a back end algorithm predicting breakdowns and being

connected to a breakdown service, the car has the ability

to use an outbound service intervening via phone, SMS, or

push notifi cation on the connected car app.

5. Safety: These functions intimate the driver of

external hazards and internal responses of the vehicle to

hazards. Basically, in case you have had an unfortunate

crash, your car immediately makes an emergency call

(referred to as e-call) to the responsible call center and

reports the incident (emergency breaking, lane keeping,

adaptive cruise control, and blind spot object identifi cation).

6. Entertainment: This involves integrating content

from various sources on the entertainment unit for the

passengers (smartphone interface, Wi-Fi hotspot, music,

video, Internet, social media, and mobile offi ce).

7. Driver Assistance: These functions comprise of

partially or fully automatic driving. There are in-car speech

recognition or voice activation systems which aim to remove

the distraction of looking at your mobile or car dashboards

while driving (operational assistance or autopilot in heavy

traffi c, in parking, or on highways).

8. Comfort and Well-being: This manages driver’s

comfort and current state to drive (fatigue detection,

automatic environment adjustments to keep drivers alert,

and medical assistance).

It’s obvious to think at this moment that your car

doesn’t do any of this, or possesses just a few functions

but not all. This has already become a hot space to follow,

and automotive OEMs are racing with one another to roll

out these functionalities in more and more models, without

limiting them to their premium ones.

So, let’s take a step back and see how this came into

existence. What was the infl ection point which led to its

discovery?

General Motors was the fi rst automaker to bring the

fi rst connected car features to market with a program called

OnStar in 1996. They started this with the Cadillac DeVille,

Seville, and Eldorado.

In the beginning, the program was limited to

notifi cations of crashes to emergency responders, locating

the vehicle, and roadside assistance. While this began as an

after-market model, i.e., customers can opt for these services

and choose to pay for them like they do with additional

accessories for their cars. In 1998, GM improved the OnStar

service with a change to factory-installed models that allow

for hands-free calling and voice recognition.

During these years, other OEMs geared themselves

up and launched similar suites of services. In 1999,

Mercedes-Benz launched its TeleAid telematics program

with emergency response roadside assistance and location

of stolen vehicles. By 2003, connected car services included

vehicle health reports, turn-by-turn directions, and a network

access device. The OnStar program was such a huge success

that in 2015, OnStar had processed one billion requests

from customers. It’s safe to consider it the benchmark

program in this space.

Clearly, this area has enough promise and has already

delivered value in various ways in different parts of the

world. The strong, steady, and slow world of automotive has

been totally rocked by new technology. It defi nitely gave it

an extra pair of supersonic wings to fl y faster than ever.

There’s a huge ecosystem of connected car services

and mobility services startups, technology giants, consulting

companies, and fi nally, automotive OEMs that are working

tirelessly to modernize the way we commute. SV

Actuonix Motion Devices ���������������������������������� 29

ExpressPCB �����������������������������������������������������������15

goBILDA ��������������������������������������������������������� 37, 75

Hitec RCD USA, Inc� ����������������������������������������������2

IM Service ����������������������������������������������������������� 37

LDG Electronics ������������������������������������Back Cover

M�E� Labs ������������������������������������������������������� 37, 69

Tormach ��������������������������������������������������������������� 36

WONWOO Engineering ���������������������������������������3

ADVERTISER

INDEX

New Products Continued from page 27

1. Six operating modes: torque control; velocitycontrol; position control; extended positioncontrol; current based position control; andPWM control.

2. Profile control for smooth motion planning.3. Improved heatsink featuring an aluminum

case.4. Hollow back case minimizes cable stress

(three-way routing).5. Direct screw assembly to the case (without

nut insert).6. Energy saving; reduced current from 100 mA

to 40 mA.7. 28.4% reduced volume compared to the

MX-106.8. Supports synchronous control mode.

For further information, contact:

ROBOTISwww.robotis.com

Dual 60A Speed Controller

The Sabertooth Dual Drive Board now available from AndyMark is

acceptable for high powered robots up to 120 lbs in combat or up to 1,000 lbs for general-purpose robotics. It can supply two DC brushed motors with up to 60A each. Peak currents of 120A per channel are achievable for a few seconds. Overcurrent and thermal protection integrated into the controller ensure you’ll never have to worry about killing the driver with stalls. Dual motor control can be operated via analog voltage, radio control, serial, and packetized serial. Independent speed and direction operating modes make it the ideal driver for tank-style robots. Price is $190.

The operating mode is set with the onboard DIP switches so there are no jumpers to lose and screw terminals for connections mean no soldering is required. This controller also has synchronous regenerative capabilities. The regenerative topology means that your batteries get recharged whenever you command your robot to slow down or reverse. Sabertooth also allows you to make very fast stops and reverses, giving your robot a quick and nimble

edge. A built-in 5V 1A switch-mode BEC can supply power for your receiver or microcontroller, as well as 3-4 standard analog servos. The lithium cutoff mode allows Sabertooth to operate safely with lithium-ion and lithium polymer battery packs. This component is not legal for the FIRST Robotics Competition and FIRST Tech Challenge robots. Features include:

• Synchronous regenerative drive• Ultrasonic switching frequency• Thermal and overcurrent

protection• Lithium protection mode

• Two-channel 60A continuous delivery

Specifications are:• Input: analog, R/C, simplified serial, packetized serial• Voltage: 6-30V nominal, 33.6V absolute maximum• Weight: 0.664 pounds

For further information, contact:

AndyMarkwww.andymark.com

72 SERVO Issue-1.2020

Some Of Our Most Popular Books On RoboticsRobot Buildingfor Dummies

Robot Builder’s Bonanza - 5th EditionRobot Programmer’s Bonanza

The Ultimate GuideTo DIY Animatronics

Building With Virtual LEGO

SERVO On CD

To Order Visit www.servomagazine.comTo Order Visit www.servomagazine.comor call 1-800-783-4624or call 1-800-783-4624

SERVO Issue-1.2020 73

https://www.servomagazine.com

75

AT-1000PROII

QRO Auto Tuner to 1000W

� Switch L Network� Dual Antenna� 1000W SSB / 350 W Digital� USB Control

AT-600PROII

600 Watts to Mid Size Amps� Dual Bargraph� 1.8 to 54MHz� 600W SSB / 200W Digital� USB Control

AT-200PROII

200 Watts Desktop� Tunes 10:1 SWR� 2 Year Warranty� 250W SSB / 100W Digital

High Power Desktop

AT-100PROII

� Dual Bargraph� Auto / Semi-Auto Mode� 125W SSB / 30W Digital

Zero Power - Go Box Ready!IcomBalun / Unun

Z-100 PLUS

� Low Cost� Highly Portable� 125W SSB/30W Digital

Designed for portable and low power applications -zero current drawn once tuned.

Z-11PROII

� LED SWR Indicator� 10:1 SWR� 125W SSB/30W Digital

Z-817

� FT-817/818 Compatible� Operates on 4 AAs� 20W SSB/5W Digital

IT-100

� AH-3 & AH-4 Compatible� Includes Interface Cable� 125W SSB / 30W Digital

Tuner dedicated to Icomradios with seamless

integration.

� RU 1:1 UNUN� RU 4:1 UNUN� RU 9:1 UNUN� RBA 4:1 BALUN� RBA 1:1 BALUN� 200W SSB

ANTENNA MATCHING

ACCESSORIES

Special! $229.99 FREE

Shipping

LDG YT-1200With FREE 500mA PowerSupply and FREE Shipping

Call Main Trading1-903-737-0773 +

BEST PRODUCTS. BEST VALUE. BEST WARRANTY. CONTACT YOUR FAVORITE DEALER TODAY!

support@ldgelectronics.com 410-586-2177 www.ldgelectronics.com

R&L Electronics 800-221-7735

Special! $149.00

LDG YT-100

Our Most PopularDesktop Tuner