Propulsion Unit of a 3DOF Helicopter

Gustav LingJesper Persson

Division of Fluid and Mechatronic Systems

Bachelor ThesisDepartment of Management and Engineering

LIU-IEI-TEK-G–15/00854—SE

Propulsion Unit of a 3DOF Helicopter

Bachelor Thesis in MechatronicsDepartment of Management and EngineeringDivision of Fluid and Mechatronic Systems

Linköping Universityby

Gustav LingJesper Persson

LIU-IEI-TEK-G–15/00854—SE

Supervisors: Martin HochwallnerIEI, Linköping University

Examiner: Magnus SethsonIEI, Linköping University

Linköping, 1 June, 2015

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c© Gustav LingJesper Persson

AbstractThis bachelor thesis is a part of a bachelor project which includes building, pro-gramming and controlling a 3DOF tandem helicopter.

This particular report deals with the propulsion units, i.e. the motors andpropellers of the helicopter. It covers the process of how to determine the mostsuitable propulsion units for the rig that eventually will enable it to run.

To achieve this, different data have been processed. Torque and thrust are twoimportant parameters that have been studied. The data have been acquired bydifferent tests, e.g. thrust measurements from a thrust rig. Also more complexanalysis such as Blade Element Theory and Actuator Disk Theory have beencarried out in order to determine the behaviour of the propulsion units. Studydata sheets and databases was also a part of the work.

The result of this work was two equal propulsion units which were mounted inthe helicopter. They proved to work satisfactory and provided wanted dynamicsto the system.

v

Acknowledgments

We want to give a special thank you to our supervisor, Martin Hochwallner, forall the support, suggestions and guidance throughout the entire project. We aregrateful for all the components getting ordered with help from Hochwallner.

We also want to thank the personnel in the workshop for helping us manufac-ture the parts for the helicopter rig and managed to do this in time.

Also a thank you to our examiner Magnus Sethson for arranging the interestingfield trip to CybAero.

Finally a big thank you to the rest of the project group for excellent groupdynamics, cooperation and lots of fun.Linköping, June, 2015

Gustav LingJesper Persson

vii

Abbreviations3DOF 3 Degrees Of FreedomRig Entire unitHelicopter The unit which is mounted at the end of the arm where

the motors and propellers are placedPropulsion Unit Motor and propeller mounted togetherTandem Helicopter Helicopter with two main rotorsrpm Revolutions per minuteAC Alternating currentDC Direct currentRC Remote controlFBD Free body diagram

Contents

1 Introduction 11.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.3 Delimitations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11.4 Method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21.5 Structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31.6 Safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 Theoretical Background 52.1 Mechanical Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 52.2 Variable Mechanical Parameters . . . . . . . . . . . . . . . . . . . 62.3 System Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72.4 System Specifications . . . . . . . . . . . . . . . . . . . . . . . . . . 72.5 Overall System Performance . . . . . . . . . . . . . . . . . . . . . . 8

2.5.1 Propeller Dynamics . . . . . . . . . . . . . . . . . . . . . . 8

3 The Propulsion Unit 93.1 Prelude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 93.2 The Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

3.2.1 Different Electric Motors . . . . . . . . . . . . . . . . . . . 93.2.2 General Principle of a DC Motor . . . . . . . . . . . . . . . 93.2.3 The Brushed DC Motor . . . . . . . . . . . . . . . . . . . . 103.2.4 The Brushless DC Motor . . . . . . . . . . . . . . . . . . . 11

3.3 Provided Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 123.3.1 Analysis of Provided Motor . . . . . . . . . . . . . . . . . . 13

3.4 The Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 143.4.1 Fixed or Collective Pitch? . . . . . . . . . . . . . . . . . . . 143.4.2 Estimation of Thrust . . . . . . . . . . . . . . . . . . . . . . 153.4.3 Different Propellers . . . . . . . . . . . . . . . . . . . . . . . 163.4.4 UIUC Propeller Database . . . . . . . . . . . . . . . . . . . 163.4.5 Performance Plots . . . . . . . . . . . . . . . . . . . . . . . 173.4.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . 183.4.7 Blade Element Theory . . . . . . . . . . . . . . . . . . . . . 183.4.8 Blade Element Theory Evaluation . . . . . . . . . . . . . . 22

ix

3.5 Choice of Propeller . . . . . . . . . . . . . . . . . . . . . . . . . . . 233.5.1 About the Direction of Rotation . . . . . . . . . . . . . . . 233.5.2 Final Chioce . . . . . . . . . . . . . . . . . . . . . . . . . . 23

4 Measuring the Thrust 254.1 Thrust Rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

4.1.1 Idea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.2 Measuring Thrust in the Thrust Rig . . . . . . . . . . . . . . . . . 26

4.2.1 Assumptions . . . . . . . . . . . . . . . . . . . . . . . . . . 274.2.2 Outcome of the Propeller Data . . . . . . . . . . . . . . . . 274.2.3 Dynamics of Different Propellers . . . . . . . . . . . . . . . 29

4.3 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29

5 Integration of the Propulsion Units 315.1 Propeller Mount . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

5.1.1 Integration . . . . . . . . . . . . . . . . . . . . . . . . . . . 31

6 Result, Analysis & Discussion 356.1 Result . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

6.1.1 Analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 356.1.2 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 376.1.3 Ethics & Society . . . . . . . . . . . . . . . . . . . . . . . . 37

Bibliography 39

A Matlab Code 41A.1 Matlab Code for the Database Calculations . . . . . . . . . . . . . 41A.2 Matlab code for the Blade Element Theory . . . . . . . . . . . . . 42

List of Figures1.1 Rough time division . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2.1 Principle Design of the Rig . . . . . . . . . . . . . . . . . . . . . . 62.2 Side view of the rig . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

3.1 Correlation between Torque and Speed of a DC motor. . . . . . . . 103.2 Force on a conductor in a magnetic field . . . . . . . . . . . . . . . 113.3 Principle design of a brushless dc motor . . . . . . . . . . . . . . . 123.4 The provided Maxon EC-max 40 . . . . . . . . . . . . . . . . . . . 133.5 Stream Tube . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 153.6 Plot of thrust versus rpm . . . . . . . . . . . . . . . . . . . . . . . 173.7 Plot of power versus rpm . . . . . . . . . . . . . . . . . . . . . . . 173.8 Plot of Torque versus Rpm . . . . . . . . . . . . . . . . . . . . . . 183.9 Performance plot with the given motor and a suitable propeller . . 193.10 Principle Propeller Blade . . . . . . . . . . . . . . . . . . . . . . . 203.11 XFLR5 Plot with Cl versus α at different Reynolds Numbers . . . 213.12 XFLR5 Plot with Cd versus α at different Reynolds Numbers . . . 223.13 Different Propellers . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

4.1 Thrust rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 254.2 Thrust rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 264.3 FBD of the thrust rig . . . . . . . . . . . . . . . . . . . . . . . . . 274.4 APC MRP 10" x 4.5" propeller test . . . . . . . . . . . . . . . . . . 284.5 APC 11" x 4.7" Slowflyer propeller test . . . . . . . . . . . . . . . . 28

5.1 The Propeller Adapter . . . . . . . . . . . . . . . . . . . . . . . . . 325.2 The integrated propulsion unit . . . . . . . . . . . . . . . . . . . . 33

6.1 The final rig . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 366.2 Measured Thrust in the Helicopter . . . . . . . . . . . . . . . . . . 37

List of Tables3.1 Maxon EC-Max 40 Data . . . . . . . . . . . . . . . . . . . . . . . . 133.2 Vectors for geometrical data . . . . . . . . . . . . . . . . . . . . . . 20

Chapter 1

Introduction

1.1 BackgroundThe institution of Fluid and Mechatronic Systems at Linköping University, Swe-den, has requested a prototype rig to investigate principles of automatic controland the dynamics of a tandem rotor helicopter system.

The rig, which is limited to 3DOF, offers a good simplification of a realistic full-scale system for evaluating performance of different automatic control principles.

The system could be used as a tool for laboratory classes in various controlcourses. The students could for example, as an exercise be given the task ofcalculating certain controller parameters with respect to some given specifications.

This particular thesis is written as a part of this project and will focus specif-ically on the propulsion units, which is the combination of the motor and thepropeller that powers the helicopter.

1.2 ObjectivesThe goal of the main project is to design and build a test rig to analyze and controla 3DOF tandem helicopter.

The goal of this part of the project is to find a satisfying combination of a motorand a propeller suitable for the entire system, and providing sufficient thrust anddynamics to the system.

A more personal goal is to increase theoretical knowledge about how a propul-sion unit works and its characteristics. And finally, to get a feeling about theprinciple of working as a part of a project and the engineering work process.

1.3 DelimitationsTo make the project objectives achievable and not too comprehensive, due to timeinsufficiency, delimitation’s regarding equipment and materials for building thetest rig was necessary.

1

2 Introduction

Generally, the test rig is limited to 3DOF. The available hardware to build thetest rig is limited to that provided by the institution of Fluid and MechatronicSystems, Flumes.

Furthermore, the test rig should be built in a reasonable size, i.e, portable.And last, patents will not be observed.The propulsion units are limited to indoor use only. Since there are many

electrical components involved, the propulsion units should not be exposed tomoist and low temperatures since it can affect the performance of the unit.

1.4 MethodAs a part of the whole project, this thesis only focus on the propulsion units. Thegroup, consisting of two people, have been working close together throughout theproject. Likewise with the rest of the groups in order to adapt the respective partsto each other so that it would lead to a fully functioning rig.

In order to gain an understanding about the principles of a propulsion unit andachieve adequate knowledge there have been extensive research about the parts ofa propulsion unit, both in the University library and on the Internet. The group’ssupervisor has been supporting and guiding with knowledge and experience fromthe beginning to the end of the project.

Specifically this project, instead of only theory, is also based on tests andcalculations. In order to obtain relevant data different tests have been carried out,providing useful data and insights of how the different parts correlated to eachother.

Tests that have been carried out was for example to achieve a certain thrustfor a given rpm. Furthermore, to some extent, theoretical analysis, i.e. the BladeElement Theory, gave an idea what performance to expect from the propulsionunits. This were essential information for the project.

In the final phase of the project, all groups worked together with the assemblingof the rig to get it up and running.

The project have been going on continuously during a spring semester. Theoverall time consumption has been the work with the testing of the motors andpropellers, as well as on assembling the rig and writing the report.

Since this project involves a considerable amount of work, a brief time divisionwas made in order to give a rough approximation of how the time should be spent.This is displayed in figure 1.1.

1.5 Structure 3

15%

15%

20%

10%

40%

Initial Time Division

Research

Calculations

Tests

Assembling

Report Writing

Figure 1.1: Chart illustrating a rough time division between different parts of theproject.

1.5 StructureThis thesis is, as mentioned before, written as a part of a larger project. A briefdescription of the project is described in this introduction chapter. Chapter 2 bringup information about the entire system where the propulsion units should be ableto fit in. From the entire project’s point of view, chapter 2 provides necessarybackground information about the expectations of the propulsion units. Chapter3, which is the core part of the project, thoroughly describes the work process.This chapter is followed by chapter 4 which explain tests that was carried out foranalyzing the theoretical results from chapter 3. Furthermore, chapter 5 explainsthe mechanical integration of the propulsion units. Finally, chapter 6, describesthe result of the project followed by analysis and discussions. Worth mentioning,some results and analysis have been written throughout the whole report makingit easy to follow.

1.6 SafetyThroughout the project different tests have been carried out. Thus there weresome safety issues that had to be taken into account, e.g due to high speeds up to10 000 rpm, and fairly large power sources.

Therefore some preparations was made before starting. To avoid any injuriesand unexpected events, preventative measures was carried out.

If any part was to unexpectedly fail while running the propulsion units, animportant measure was to use a cover close to the propulsion units. Therefore amakeshift protective wall enclosing each propulsion unit was constructed in orderto minimize unexpected events. The persons working near the propulsion units

4 Introduction

was also obligated to use safety glasses.An emergency switch had to be connected to the rig’s power supplies to quickly

be able to stop operation in case of unexpected events.The motors can become warm after extensive usage, use caution.Since there is fairly high power sources, any contact with water or any other

fluids could be dangerous. Therefore, no fluids were allowed around the rig.The rig weighs around 30 kg. One have to be careful while carrying it to avoid

any damage.

Chapter 2

Theoretical Background

2.1 Mechanical DesignThe mechanical design of the test rig was determined by the project group tolook like figure 2.1. In short, this design was selected because of the limitationsin degrees of freedom. By choosing this design the helicopter unit could have acontinuous forward motion by turning around the main axis of the rig, meaningno limitation of angle b in figure 2.1.

Furthermore, it can be seen in figure 2.1 that the arm which extends to thehelicopter is considerably balanced by a counterweight placed on the other sideof the pivot point. This means that the propulsion units wont have to providethrust in order to independently lift the helicopter by themselves, because therewill be a moment from the counterweight which will help lifting the helicopter. Thehelicopter also has continuous power connection through wiring in the structurewhich means it is not dependent on a limited power source.

It should also be mentioned that the rig is to be controlled automaticallythrough a controller which will rely on sensors measuring the angels marked a, band c in figure 2.1.

5

6 Theoretical Background

ab

c z

Counterweight

Stand

Arm

Helicopter

Propulsion unit

Figure 2.1: The principle design of the test rig displaying the three degrees offreedom denoted a, b and c. Note the helicopter and the counterweight positionedat each end of the arm. The arm pivots around the point were the stand connectsto the arm.

2.2 Variable Mechanical ParametersConsidering the difficulties associated with calculating exactly what thrust anddynamics one could expect from the propulsion units in advance, the rig wasdesigned in such a way that a few critical parameters could be changed after thecomplete rig was assembled. Those were:

• The mass of the counterweight

• The lever of the counterweight

• The lever of the helicopter

• The lenght of the helicopter pivot arm marked z in figure 2.1

It was initially said that the counterweight should compensate the weight of thearm and the helicopter should provide enough thrust to be able to lift itself. Worthmentioning is that the mechanical design of the rig, which was done by anotherpart of the group, was going along at the same time as different propulsion unitswere analysed. This was carried out early in the project and it was relativelyeasy to scale all mechanical dimensions to fit the propulsion units which wereconsiderably critical for the final dimensions. For example, heavier and morepowerful propulsion units would require a stronger and larger structure comparedto lighter ones. Because of that, communication with the mechanical design group

2.3 System Control 7

during the first part of the project was essential. However the adjustability of thecounterweight also meant that it easily could compensate for any mismatches withthe mechanical design. E.g. if the propulsion unit would not be able to provideenough thrust making the helicopter lift, it was supposed to be easy adjusting themoment from the counterweight to make the thrust sufficient enough for take off.

2.3 System ControlChanging the thrust on the propulsion units were the only way to change the stateof the helicopter meaning that the signals out from the control system were onlygoing to the propulsion units. Thus it was necessary to understand in what waythe propulsion units would perform to affect the angels shown in figure 2.1. Thelist below explains briefly how the propulsion units were supposed to perform dueto make the helicopter move and change position.

• Both propulsion units provides equal thrust making the helicopter changeits elevation, meaning, increasing or decreasing angle a in figure 2.1.

• A difference in thrust between the propulsion units making the helicopterpitch, meaning increasing or decreasing angle c in figure 2.1.

• When the helicopter pitches, meaning, angle c is not equal to 90 degrees, thehelicopter will change the travel angle marked b in figure 2.1

2.4 System SpecificationsAt the beginning of the project a list of specifications for the rig was set up. Belowis a brief summary of the list including the entries which affected the selection ofpropulsion units.

• Mechanical

– Minimum of 270 degrees of rotation about the travel axis.– 45 degrees of angular displacement about the pitch axis, positive and

negative.– 30 degrees of angular displacement about the elevation axis, positive

and negative.– Mechanical three axis locking system to enable power up from a known

reference point.– Maximum weight of 40 kg.– The entire system should be able to fit and function in a space the size

of 3x3x2 meters.

• Performance

8 Theoretical Background

– Tangential acceleration and speed about the travel axis of at least 1m/s2 and 1 m/s respectively.

– Tangential acceleration and speed about the elevation axis of at least 1m/s2 and 1 m/s respectively.

– Angular acceleration and speed about the pitch axis of at least 2πrad/s2 and π/4 rad/s respectively.

A direct conclusion from the list above was that the propulsion units could not beto large. As mentioned, the entire rig was somehow dimensioned with respect tothe propulsion units. Larger propulsion units would lead to a larger and heavierrig. The specification list states a maximum weight of 40 kg and a maximumoperation area of 3x3x2 meters.

2.5 Overall System PerformanceRegarding the system’s performance it was preferable that the helicopter, or morecorrect its propulsion units, could generate as much thrust as possible. This meantthat the moment from the counterweight could be smaller which in return wouldprovide a faster system response around axis of elevation and travel. This dueto the distance a in figure 2.2. A greater mass at a greater distance leads to anincreased inertia around the axis of travel and elevation. As familiar, a greaterinertia means that a greater force must be applied to change its current state.However, it should be mentioned that a slower system is considerably easier tocontrol, but less exciting.

Fc

Ft

Fg

Oa b

Figure 2.2: Displaying the forces which contributes to moments around the pivotpoint marked O.

2.5.1 Propeller DynamicsConsidering that the control system must be able to quickly alternate the thrust,it is preferable that the propeller dynamics is faster than the helicopter dynamics.This had to be kept in mind during the propulsion unit selection process since itwould make the helicopter easier to control.

Chapter 3

The Propulsion Unit

3.1 PreludeUp to this point there has been specifications regarding the propulsion units per-formance from a complete system perspective. This is however very importantinformation upon which the selection was based.

The propulsion unit itself consist of a propeller mounted upon a motor shaft.The motor spins the propeller at different speeds which provides various thrust.When the thrust alternates, the helicopter moves around its axis. As stated before,it is this thrust the control system will regulate in order to make the helicopterfollow a reference signal.

3.2 The Motor

3.2.1 Different Electric MotorsTo understand all the relevant variables for the selection of an appropriate motor,it is interesting to know some background facts about common electric motors.

Today’s market offers a wide selection of different electrical motors. A commonone is the DC motor. The DC motors differ significantly when it comes to size,performance, appearance and functionality.

3.2.2 General Principle of a DC MotorThe DC motor is powered by direct current. Simplified, it works as a converterfrom DC to mechanical energy, i.e. torque. It is a common used motor due toits high torque, ability of speed control and good speed-torque characteristics [11,p.762]. Basic speed-torque behaviour of a DC motor is shown in figure 3.1.

The DC motor can be found in many areas of use, e.g. household appliancesto more advanced products such as robotics, measure and analysis equipment,machines, etc.[5].

9

10 The Propulsion Unit

DC motors are commonly constructed according to two different principles,brushed and brushless.

Speed in rpm

Torq

ue in N

m

No load speed

Stall Torque

Max Power, Pmax

ω

Figure 3.1: Correlation between Torque and Speed of a DC motor.

What is often limiting a DC motor is the current which is related to the torqueaccording to equation 3.1, where T is the torque and i is the current. Kt is thetorque constant which is a motor parameter. Every motor has a specification ofwhat maximum current it can withstand. This has to do with the motor windings,which becomes overheated if exposed to a large current over a certain period oftime.

T (t) = Kt i(t) (3.1)

3.2.3 The Brushed DC MotorThe very basic operating principle of a brushed DC motor is based upon electricityand magnetism. According to Lorentz law, equation 3.2, a conductor of length lcarrying current of magnitude i in a magnetic field B is exposed to a force Fdepending on the angle α between the conductor and the magnetic field. Basicallydescribed in figure 3.2.

F = Il×B (3.2)

Brushed DC motors are characterized by its commutators. The commutatoris a type of mechanical switch which together with the coil windings creates arotating armature. In a brushed DC motor the polarity in the stator is fixedwhile the polarity in the armature is changing with help from the commutator[9, p.15-16]. Brushes supply the armature through physical connection with thecommutator, hence the name.

The torque from the motor is obtained by the force F which increases accordingto equation 3.2 and its lever which is the height of the armature measured fromthe center of the shaft. The greatest torque is obtained when the conductor is

3.2 The Motor 11

N pole S poleF

Magnetic Field

B

i

Current

Trough

Conductor

Current i

Field B

Force B

α

Figure 3.2: Force on a conductor in a magnetic field [11, p.763].

perpendicular to the magnetic field. In a real brushed DC motor the armatureconsists of many coil windings which makes the torque relatively constant. Thebenefit of using a brushed motor is that it is cheap and does not necessarily needa controller of its own. On the other hand the motor needs more maintenance,e.g. the brushes wear out, it emits a loud noise and it has a limited efficiency dueto the brushes [10].

3.2.4 The Brushless DC MotorUnlike the brushed DC motor the basic principle of the brushless motor is rotatingpermanent magnets, i.e. the rotor or armature, on the contrary to the brushed DCmotors [11, p.768]. The construction of the brushless DC motor is quite simplebut to get the motor running it needs both a controller and a some hall sensors.

A brushless DC motor can have numerous coils, stationed in a circular pattern,depending on which motor it is. The hall sensors measure the location of the rotorso that the controller can decide which coil to energize and thereby get a steadytorque of the rotor [3]. The principle design of a brushless DC motor is displayedin figure 3.3.

The brushless DC motor is more reliable, efficient, weighs less and emits alower noise compared to the brushed motor [3].

12 The Propulsion Unit

W1

W2W3

A

V

ABW2

I

A

1

V2

V3

I

U1-2

U2-3

U3-1 BW1

BN

Hall 1 High

Hall 2 High

Hall 3 HighM

Figure 3.3: Principle design of a brushless DC motor displaying the rotating per-manent magnet in the middle attempting to line up with the coil in front of it [6].

3.3 Provided MotorThe goal of this project is to provide the rig with the most suitable propulsionunits. A main part of this goal is the motor, which is somewhat half the propulsionunit.

Early in the project it was noted that the University had a few motors to pro-vide, Maxon EC-Max 40, which could fit this project. This was a very interestingopportunity since they were "for free" and could be used and tested directly with-out having to wait for delivery. However, to decide whether they were suitable forthe rig a few parameters had to be analysed and tested. A summary of importantparameters of the Maxon EC-Max 40 is presented in table 3.1.

3.3 Provided Motor 13

Table 3.1: Relevant data for the EC-max 40 [7].

Power 120 WVoltage 48 VNo load speed 10100 rpmNo load current 310 mANominal speed 9250 rpmNominal torque (max. continuous torque) 170 mNmNominal current (max. continuous current) 4.06 AStall torque 2090 mNmStall current 46.7 AMax. efficiency 85 %Torque constant 44.8 mNm/ASpeed constant 213 rpm/VSpeed / torque gradient 4.89 rpm/mNmNumber of phases 3Weight 720 gLength 88 mmDiameter 40 mmShaft Diameter 6 mmShaft Length 20 mm

Figure 3.4: The provided Maxon EC-max 40 brushless DC motor connected withthe encoder to the right. c©Marcus Almén

3.3.1 Analysis of Provided MotorThe provided Maxon EC-Max 40 is a brushless DC motor equipped with an en-coder. Maxon control units for regulating the speed of each motor was also avail-able from the University.

The main characteristics that immediately could be analyzed was the motorsweight of 720 grams. Considered as significantly heavy, this could affect the spec-ifications regarding the size of the complete rig. However, after consulting themechanical group, who analyzed the effect on the structural dimensions, it was

14 The Propulsion Unit

confirmed that the rig still would fulfill the mechanical specifications, although itwould be bigger than initially expected. To directly conclude anything about theother parameters was almost impossible since there was at this point no informa-tion about the load.

The motor was to be able to spin a propeller at a speed which would providea needed thrust. Because of the shape of the propeller it produces not only thrustwhen rotating in air but also drag. To deal with the drag at a certain rotationspeed, the motor must be able to provide sufficient torque. To know anythingabout the torque a few details about the propeller had to be looked into.

3.4 The Propeller

There were many ways to begin the propeller selection process. For instance, thepower rating from the motor could be used together with an estimation of desiredthrust to calculate an approximation of the propeller diameter. But since it wasfamiliar that the provided motor was rather large and heavy, it was decided tobase calculations on the largest propeller that would fit in order to maximize thethrust. This was estimated to around 10" or 0,254 m in diameter. Propeller datais commonly given in inches, and therefore that unit will be used throughout thisreport.

3.4.1 Fixed or Collective Pitch?

During early research of RC-helicopters and drones on the Internet, there werea few important observations made. Basic RC-helicopters and most drones usepropellers with a fixed pitch. The pitch is the length the propeller travels duringone revolution around its through axis. For a better understanding, consider thelength a certain screw travels when tightened one turn. The fixed pitch helicopterschanges the thrust by changing the rotation speed of the propeller. As a result,the thrust increases with increasing speed.

On the other hand, real helicopters and also more advanced RC-helicopters usea propeller, or more correct, a rotor that alternate the pitch on all the blades atthe same time using a collective [4, p.81]. When using this principle, the propellerrotates at constant speed and the pitch is instead changed on all blades at thesame time generating an increase or decrease in thrust.

The benefit with the fixed pitch propeller is that it does not require the complexmechanics that is needed to alternate the pitch. However the disadvantage is thatthe propeller, due to its inertia, can not change its rotation speed momentarily.This means that it will be a delay before the wanted thrust is achieved. The delayis however very small when using small diameter lightweight propellers. Due tothis, the decision was to use a constant pitch propeller, and it was preferable thatit would be as light as possible to keep the inertia manageable.

3.4 The Propeller 15

3.4.2 Estimation of ThrustAfter deciding a maximum diameter of the propeller, an estimation of how muchthrust one could expect from the propellers had to be carried out. Since there is awide range of different propellers to choose from on the market it was not possibleto buy and test them all.

There are several mathematical theories that provides this information. Oneof them, which is probably the simplest, is called Actuator Disk Theory [4, p.63].

This theory is based upon application of the flow momentum conservationprinciple. The propeller is here exchanged with an infinite thin actuator disk andthe static pressure will be assumed to increase instantly over the disk. The disk isplaced in a contracting stream tube through which the air stream of interest willflow according to figure 3.5. This theory is used for making a rough estimation of

V0

A3

p0

A1

p1 p2

V1

p0

V3

A0

0 1 2 3

const.

Figure 3.5: The principle stream tube used in the Actuator Disk Theory [4, p.65].The propeller is replaced with an infinitely thin actuator disk with area A1 markedin the figure.

what maximum thrust could be expected from a propeller with a certain diameter.However, for the theory to be valid some limitations and simplifications needed

to be done [2, p.69]:• An incompressible, perfect fluid.

• Uniform fluid flow properties. One-dimensional flow.

• Continuous-flow velocity and pressure everywhere, except over the disk.

• The flow in front of and behind the disk are lossless. Bernoulli’s equationscan be applied in these regions.

• The lines of the stream tube in figure 3.5 defines the limits of what air flowsthrough the disk and which does not

Taking the above criteria in account, equation 3.3 can be used [4, p.67] to make arough estimation of the thrust:

P0 = F0w0 =

√F 3

02ρA1

(3.3a)

16 The Propulsion Unit

F0 = P2/30 (2ρA1)1/3 (3.3b)

Where P0, in this case, is the ideal static power required from the motor. F0 isthe ideal maximum thrust and w0 is the induced velocity. Furthermore, ρ is thedensity of air which was chosen as 1.204 kg/m3 and A1 is the area of the actuatordisk seen in figure 3.5.Using a diameter of 10" in equation 3.3 resulted in an estimated thrust of around11 N, using 120 W as static power. A considerable estimation is the usage of thegiven power rating, 120 W since this is rather an average power. The real poweris the product of current through the motor and voltage. The voltage is limitedto 48 V and the current depends on the load.

It is important to note that this theory does not take the shape of the propellerinto consideration and assumes everything is ideal. It means that the calculatedthrust is certainly higher than reality. At least, an approximation was obtainedshowing a thrust that would be sufficient to lift the motor and some part of thehelicopter frame.

3.4.3 Different PropellersThe market offered a wide range of 10" propellers in many different shapes. Oneproblem was the limited information about the specifications of the propellers.Research indicated what others recommended to RC-helicopters and what wasavailable for fast delivery in Sweden. The preliminary decision was to choose thecompany APC Propellers [1]. They were able to provide more information aboutwhat air foils they used which was necessary for more exact calculations regardingthrust and torque.

3.4.4 UIUC Propeller DatabaseAnother significant advantage with the APC Propellers is that many are availablein the University of Illinois propeller database [13]. The database consists ofmeasured data from a large amount of different RC-propellers. Static data for theAPC Thin Electric 10" x 5" [14] provides measured data of, among other things,coefficient of thrust, CT , and coefficient of power, CP , for different rotation speeds.The CT and CP are basically described as performance parameters which dependson the shape of the propeller.

The APC Thin Electric 10" x 5" is a 10" diameter propeller with a 5" pitch.It was chosen because of its high similarity with the ones that were available inSweden.

The correlation between CT and thrust is displayed in equation 3.4[4, p.72].Correlation between CP and power is presented in equation 3.5[4, p.73].

F = CT ρn2d4 (3.4)

PS = CP ρn3d5 (3.5)

The parameter F is the thrust, PS is the power and n is the rotation speedmeasured in revolutions per seconds. ρ is the density of air and d is the propeller

3.4 The Propeller 17

diameter. With d set to 10", Matlab was used to interpolate between the given rpmvalues and extrapolate outside the given range to obtain data showing a correlationbetween rpm versus thrust and power. There was also a plot made with the rpmversus torque using the same Matlab script and equation 3.6. The resulting plotsare shown in figures 3.6, 3.7 and 3.8. Since these plots are based upon measureddata of CT and CP they are considered very reliable. The Matlab script used isprinted in appendix A.

PS = Qω (3.6)

3.4.5 Performance Plots

Rotation Speed in RPM

2000 3000 4000 5000 6000 7000 8000 9000 10000

Th

rust

in N

ew

ton

0

5

10

15Thrust vs RPM

Figure 3.6: Plot showing thrust with respect to rpm of the APC Thin Electric 10"x 5" propeller.

Rotation Speed in RPM

2000 3000 4000 5000 6000 7000 8000 9000 10000

Po

we

r in

Wa

tt

0

20

40

60

80

100

120

140

160

180

Power vs RPM

Figure 3.7: Plot of power versus rpm for the APC Thin Electric 10" x 5" propeller.

18 The Propulsion Unit

Rotation Speed in RPM

2000 3000 4000 5000 6000 7000 8000 9000 10000

To

rqu

e in

Ne

wto

n M

ete

r

0

0.02

0.04

0.06

0.08

0.1

0.12

0.14

0.16

0.18

0.2Torque vs RPM

Figure 3.8: Plot of torque versus rpm for the APC Thin Electric 10" x 5" propeller.

3.4.6 SummaryThese plots were of significant interest and presented many interesting findings.Firstly, it should be noted that none of the curves display linear characteristicsbut rather a second degree behaviour. This was interesting for the control systemgroup which also had interest in the correlation between thrust and rpm.

This data, in comparison with the data of the given motor, outlined the limitswithin which the propulsion units could perform. This is displayed in figure 3.9.

A few important parameters could be set from figure 3.9. The torque curvecrosses the border of the continuous operation area somewhere around 0.155 Nmand this occurs at a rotation speed of about 8300 rpm. During that speed, thepropellers will provide approximately 10 N of thrust. This means, that if theprovided motor was to be used with an APC Thin Electric 10" x 5" propeller, amaximum thrust close to 10 N could be expected. There might be some reactionsdue to the high proximity to the value of 11 N approximated with the actuatordisk theory. This has to do with the power rating of the motor. The power ratingof electrical motors is not, as stated before, the maximum power which the motorcan provide but rather an average load power. As seen in figure 3.9, the powerneeded to spin the propeller at 8300 rpm is approximately 140 W. The providedMaxon motor is capable of providing around 150 W continuously at 8300 rpm.This may not be the case when the motor works at its highest efficiency, due tohigher heat losses. The motor was however not supposed to provide maximumtorque during all time of operation.

3.4.7 Blade Element TheoryAnother way to estimate the performance of a certain propeller is to use the BladeElement Theory. This is a mathematical method that is more accurate than theActuator Disk Theory but also more complex. The very basic principle of the

3.4 The Propeller 19

Power in Watt

0 50 100 150

Rota

tion S

peed in R

PM

0

2000

4000

6000

8000

10000

12000RPM vs Power

Thrust in Newton

0 2 4 6 8 10 12 14 16 18 20

Rota

tion S

peed in R

PM

0

2000

4000

6000

8000

10000

12000RPM vs Thrust

Torque in Newton Meter

0 0.05 0.1 0.15 0.2 0.25 0.3 0.35

Rota

tion S

peed in R

PM

0

2000

4000

6000

8000

10000

12000Torque vs RPM

Performance Chart

Motor: Maxon EC-Max 120 W 48V

Propeller: APC Thin Electric 10x5

Torque

Thrust

Power

Red Area: Continuous Operation Range

White Area: Short Term Operation Range

Figure 3.9: Plot showing propeller torque, thrust and power curves over the con-tinuous area of operation of the provided Maxon motor.

theory is a propeller blade with known air foil which is split up, or mathematicallydiscretized, into a number of elements. The elements are then evaluated individu-ally looking at their aerodynamics. This evaluation is undertaken over the entiretyof the blade and then put together to get a good estimation of the propeller per-formance [4, p.69]. While it was expected that the theory would produce similarresults as those from the UIUC database calculations, it was interesting to explorethe similarities.

The first step in the process was to obtain geometrical propeller data. Thisdata was again retrieved from the UIUC database and the APC Thin Electric 10"x 5" propeller. The data of interest was the chord width and the pitch angle (β)displayed in figure 3.10. It should be noted that these calculations were basedupon a hover situation meaning the forward velocity equals zero and pitch angleequals angle of attack (α).

The propeller was divided into 17 segments along the blade radius of 5" or

20 The Propulsion Unit

Forward Velocity

Rota

tional Velo

city

Chord

Lin

e

Rela

tive W

ind

Thrust

Angle o

f Atta

ckPitch Angle

Chord

Width

Figure 3.10: A principle side view of the propeller blade element. Note the pitchangle and chord width.

0.127 m. Each segment with an individual pitch angle and chord width accordingto the data from UIUC [12]. The first segment from 15 to 20 percent of the radiusstarting from the center and then with 5 percent increment. Below 15 percentis the propeller hub which does not contribute to the aerodynamics substantially.The radial stations and associated geometrical data was then stored in separatevectors shown in table 3.2. Refer to appendix A for all vector data and the Matlabcode.

Table 3.2: Vectors for geometrical data at the 17 segments.

rR Proportion of Total RadiuscR Chord Widthsβ Pitch AnglesA Average airflow area of each segment

The next step was to make an estimation of the speed of rotation at which thecalculations would be valid, since there are different Reynolds Numbers at differentspeeds. Earlier calculations indicated that a speed around 8300 rpm would be themaximum for the provided motor. However, it was known that the Blade ElementTheory overestimated the thrust and underestimated the torque. Due to this, thecalculations was based on a speed of 9000 rpm to get some margin of the criticaltorque. Subsequently the air flow velocity for the respective data points of thepropeller was calculated and stored in a separate vector shown in equation 3.7.

v = 2π900060 r (3.7)

3.4 The Propeller 21

Where r is the distance along the radius to the geometric data points, calculatedin equation 3.8 and R is the radius in meters.

r = rRR (3.8)

The Reynolds Number (RN) at each station was calculated with the propellersurface estimated as a flat plate according to equation 3.9

RN = vc

ν(3.9)

Where c is the chord width for respective geometric data points, calculated inequation 3.10, and ν is the kinematic viscosity.

c = cRR (3.10)

Next step was to estimate the coefficients of lift and drag, Cl and Cd. APCPropellers states that the MRP propeller uses the Eppler E63 air foil inboards andClark-Y air foil near the tip. Inboards is around 85 percent of the propeller withrespect to centre. UIUC provides data of these air foils in their air foil database[8]. This data was then loaded into a software called XFLR5 [15] for analysis.The software was used to estimate Cl and Cd at a certain pitch angle (α), andReynolds number shown in figure 3.11 and 3.12. The Cl and Cd numbers werethen stored in separate vectors.

Figure 3.11: XFLR5 Plot with Cl versus α. Different Reynolds Numbers illustratedwith different colors. Note that in this case α = β.

22 The Propulsion Unit

Figure 3.12: XFLR5 Plot with Cd versus α. Different Reynolds Numbers showedin different colors. Note that in this case α = β.

Another interesting aspect was the area over which the air flows at each segmentcreating lift and drag. This area was calculated as average radius multiplied withaverage chord width of each segment, and was also stored in a vector A.

The lift and drag components from each section was then calculated. This wasdone using equations 3.11 and 3.12 [4, p.69].

Fl = 12ρv

2ClA (3.11)

Fd = 12ρv

2CdA (3.12)

The last task was to numerically integrate data from each section to get datafor the entire blade. To obtain the torque, the drag components of each sectionwas multiplied by the average radius of the section and then summed up. Finally,the total lift and torque was multiplied by two since it was a two blade propeller.

3.4.8 Blade Element Theory EvaluationThe final results indicated that a thrust of approximately 13 N and a torque ofapproximately 0.19 Nm could be expected. These values was very reasonable sincethe database calculation, which are very exact since they are based upon measureddata, showed 10 N and 0.15 Nm at 8300 rpm. The Blade Element calculationswere based upon a rotation speed of 9000 rpm. Therefore, it was logical that thosevalues were a bit higher. This also due to the mentioned overestimate of thrustand underestimate of torque that occurs because of some simplifications.

To obtain a curve showing a correlation between thrust or torque and rpm isalso possible with this theory. This was however not carried out since it was atime consuming process and the values of most interest were the maximum ones.

3.5 Choice of Propeller 23

3.5 Choice of Propeller3.5.1 About the Direction of RotationAnother considered critical aspect when looking at certain propellers was the di-rection of the rotation. A propeller is designed to rotate in one direction anddoes not perform well if rotated in the "wrong" direction. Since the helicopterwas to have two propulsion units, each consisting of one motor and one propeller,it was preferable that the propellers turned in different directions. This since atorque from the helicopter is required to be able to hold the motors in place whenspinning the propellers. If the motors and propellers are spinning in different di-rections these torques will eliminate each other. Although this will only occur ifthe propellers are turning at equal speed, which will be the case when hoveringor changing elevation. As mentioned in section 2.3, the motors are to turn thepropellers at different speeds when pitching the helicopter. This will in fact con-tribute to a net torque on the helicopter. This is however dealt with since thehelicopter is locked by the arm in the direction of the torque. But even thoughthe helicopter is locked in the torque direction it is not a preferable situation andtherefore it was said that the propellers should turn in different directions. Thisfact eliminated a few of the propellers available in Sweden.

3.5.2 Final ChioceAs discussed before, the propeller which the database calculations shown in figure3.9 were based on, was not available in Sweden. However a very similar propeller,the MRP 10" x 4.5", from the same company but with a slightly lower pitch wasavailable for short delivery time and in different turning directions. One turningclockwise and the other turning counterclockwise. These were ordered along withsome other propellers, some of them displayed in figure 3.13, of similar shapes andmeasurements. Since the final task was to test the propeller in a thrust rig, it wasconsidered interesting to have a few different propellers to chose from and makecomparisons.

24 The Propulsion Unit

Figure 3.13: A few of the different propellers that were ordered for testing. TheAPC MRP 10" x 4.5" is the one to the right hand side.

Chapter 4

Measuring the Thrust

4.1 Thrust RigTo validate the calculations and get exact measurements a simple thrust rig wasconstructed. The thrust rig is displayed in figure 4.1. The rig is constructed like a

Figure 4.1: Principle design of the thrust rig

90 degree wooden arm. On the top, the propulsion unit was mounted with screwsin order to get it as stable as possible while conducting tests, see figure 4.2 forthe design of the mount. As figure 4.2 displays, the neck of the mount has astreamlined design. The reason for this is that the reactive force is considerably

25

26 Measuring the Thrust

Figure 4.2: The thrust rig design displaying the mount and the streamlined neck

lower compared to a flat shaped rectangular neck. This will generate a largerthrust value while conducting the tests compared to what would be expected ofthe thrust generated by the helicopter rig.

4.1.1 IdeaThe purpose for this type of test is to obtain a correlation between the speedand thrust for controlling the motor, and to obtain a graph that illustrates thebehaviour of the propellers. To choose the most suitable propeller, tests with dif-ferent propellers were carried out. The obtained data would later be implementedin the control system for the helicopter rig.

4.2 Measuring Thrust in the Thrust RigAs mentioned before, the propulsion unit was mounted on the top of the thrustrig and tightened with screws to get the rig as rigid as possible to reduce anythrust losses when testing. The speed was then increased via the controller withan increment of 200 rpm. During the tests, the wooden arm pushed the scale andthe thrust was transferred directly onto the scale according to figure 4.3.

By using this method different values from the scale could be read. Using thevalues from the scale, the reaction force could be obtained due to the fact thatthe reaction force on the scale is proportional to the generated thrust from the

4.2 Measuring Thrust in the Thrust Rig 27

DC motor Fthrust

Fscale

L1

L2

g

FAx

FAy

A

MA

Figure 4.3: FBD of the thrust rig. The masses of the motor and the rig areassumed to be negligible.

propulsion unit. This can be proved with help from a FBD. From the FBD infigure 4.3, equation 4.1 can be obtained.∑

MA = 0 (4.1a)

L1 Fthrust − L2 Fscale = 0 (4.1b)

Fthrust = L1

L2Fscale = Fscale (4.1c)

As can be seen in figure 4.3, the lengths L1 and L2 are equal meaning that Fthrust

and Fscale are equal. With the scale values can Fscale be calculated according toFscale = mscale g = Fthrust. Finally, the gravitational force zeroes the scale andthe forces acting on the pin support, denoted point A in 4.3, are not needed forsolving equation 4.1.

4.2.1 AssumptionsThe rig was made as rigid as possible to avoid any losses in thrust due to defor-mation. Small losses in thrust will always occur since it is difficult to make thethrust rig fully rigid. However the losses in this case was assumed to be very smalland was thereby considered neglectable.

Similarly regarding the generated air flow. When testing the propulsion unitthe air flow would not be ideal due to the fact that no equipment such as a windtunnel model was used. This could induce some losses in the air flow, meaningless thrust.

4.2.2 Outcome of the Propeller DataMeasurements with different propellers was conducted and plotted in Matlab toillustrate the performance of the propellers. Matlab was also used for estimatingthe respective functions by interpolating the test results. The functions are statedin equation 4.2 for the 10" x 4.5" propeller respective equation 4.3 for the 11" x

28 Measuring the Thrust

4.7" Slowfyer propeller . Since there is a wide number of different propellers on themarket, only a few propellers were tested, see figure 3.13. Especially two propellersconsidered to be of more interest, the 11" x 4.7" and the 10" x 4.5". Performanceof these propellers are displayed in figure 4.4 and 4.5.

y = 1.04 10−7 x2 − 9.3 10−5 x (4.2)

y = 2.6 10−7 x2 − 0.00023 10−5 x (4.3)

Speed in rpm

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Th

rust

in N

0

2

4

6

8

10

12Thrust as a function of speed

Thust data

Quadratic

Figure 4.4: Test results of the APC MRP 10" x 4.5" propeller. The y value denotesthe maximal thrust, 10.16 N for a given speed, 8600 rpm, x

Speed in rpm

0 1000 2000 3000 4000 5000 6000 7000

Th

rust

in N

0

1

2

3

4

5

6

7

8

9

10Thrust as a function of speed

Thrust data

Quadratic

Figure 4.5: Test results of the APC Slowflyer 11" x 4.7" propeller. The y valuedenotes the maximal thrust, 9.33 N for a given speed, 6400 rpm, x

4.3 Summary 29

4.2.3 Dynamics of Different PropellersAn interesting observation during the tests was the dynamics of the different pro-pellers. This had been anticipated since the project’s start, but was hard to docalculations on since there was no data available. The motors had no problemwhen accelerating and decelerating all propellers up to 11" in diameter. However,one propeller, the APC MRP 13" x 4.5", showed a bit of delay when changingspeed. Bearing this in mind, the choice was to exclude the APC MRP 13" x 4.5".

4.3 SummaryBetween the two propellers, the APC MRP 10" x 4.5" propeller was finally chosenbecause it was able to provide slightly more thrust, 10.16 N, at a speed of 8600rpm.

All propellers were tested up to the rotation speed at which they hit the motorlimitation in torque according to table 3.1. Overriding this limit would result in acurrent above the limit of 4 A in the motor windings generating overheating whichcould destroy the motor.

30 Measuring the Thrust

Chapter 5

Integration of thePropulsion Units

5.1 Propeller MountTo physically mount the propeller upon the motor shaft, an adapter was built.This had to be strong but yet have low inertia. It was lathed of steel and holeswere drilled on the sides. Small locking screws were then used in the holes to lockthe adapter on the shaft. Countersinks were made on the motor shaft, in whichthe head of the locking screws should fit. Finally the adapter was mounted uponthe motor shaft and locked in position by the locking screws. These were thenfixed with a thread locking glue to prevent them from falling out over time.

The upper shaft of the adapter was threaded so that a locking nut could beapplied to lock the propeller on the adapter. The diameter of the shaft was selectedto 6 mm since research showed that most of the propellers of interest used a 6 mmhole. The drawing of the propeller adapter is displayed in figure 5.1.

5.1.1 IntegrationThe installation of the propulsion units in the helicopter went very smooth due to agood communication with the mechanics group which had designed the helicopterto fit with the Maxon EC-Max motors. The integrated propulsion unit is showedin figure 5.2.

31

32 Integration of the Propulsion Units

Konstruerad av

Artikel nr/Referens

Ägare

Utgåva Blad

Titel/Benämning

SkalaVyplaceringjämnhet, RaGenerell yt-

Ritningsnummer

Pos nr AntalGranskad av Generell toleransGodkänd av - datum

SS-ISO2768-1

Titel/Benämning, beteckning, material, dimension o.d.

Godkänd av-datumÄndr nr

c k

unna

cad.nu

Ändringens art/Ändringsmeddelande

Kandidatprojekt HelikopterM

B

B

10

15

14,5

3

6

20

6 H7

13

3

7,5

Propeller mount

2:1GL

Gustav Ling 0735257276

Alla mått i mmMaterial: delrinAntal: 2 st

SCALE 2,000

Gängas hela vägen enl M6 standard

SECTION B-B

Gäller för båda 3mm hålen:Gängas invändigt enl M3 std

Åtdragningsriktning: In mot centrum

Figure 5.1: Drawing of the propeller adapter.

5.1 Propeller Mount 33

Figure 5.2: Entire propulsion unit consisting of the motor, the propeller and theadapter, mounted in the helicopter. One can also note the locking screw at theside of the adapter.

34 Integration of the Propulsion Units

Chapter 6

Result, Analysis &Discussion

6.1 ResultThe project has resulted in two working propulsion units which have been mountedin the final rig as figure 6.1 illustrates. Each propulsion unit consists of a MaxonEC-Max 40 brushless DC motor, one propeller adapter and one propeller. Thechosen propellers were the APC’s Multi Rotor 10" x 4.5". The complete propulsionunits proved to work in a satisfactory manner when mounted in the helicopter,making it move around providing sufficient dynamics to the system. As intended,the counterweight and the adjustability of the rig proved to work well and aftersome adjustments a fine balanced system was achieved.

6.1.1 AnalysisDuring the report, most results and analysis have been written down continuously.However, there are a few important things left to mention.

The motor was chosen mainly because it was available at the University. Itproved to work well and it was considered easy to control the speed since it wassupplied with both an encoder and a controller. If another motor had been chosenit would preferably be lighter and stronger in meaning to provide more thrust.Motors of this kind were available, but quite expensive and the shipping timescould sometimes be long. By choosing the provided motors the project could havea larger budget to spend on other important details which improved the rig.

Selecting an "optimal" propeller proved to be a very difficult task. Differentpropellers are good for different applications and operation areas. Performingcalculations on a certain propeller is a time consuming process.

The UIUC propeller database proved to be useful. It offered exact calculationson certain propellers. This data was valuable in order to make the first roughselection.

35

36 Result, Analysis & Discussion

Figure 6.1: The complete final rig.

A large part of the main project was to develop a control system to the he-licopter. This required a functioning helicopter which meant that the propulsionunits had to be completed quite early in the project. Due to this, analysis ofdifferent propellers had to be done in a limited time frame. If more time couldhave been used more propellers could have been analysed and a even better onecould have been selected.

A consequence due to lack of communication with the mechanics group led to ahelicopter construction which was not perfect in an aerodynamic fashion. Duringthe construction of the thrust rig, the shape of the motor mount turned out tohave a great impact regarding the obtained thrust. The initial helicopter had arelatively large area below the propellers which "consumed" a lot of the air flow.This led to a large loss of thrust as can be seen in figure 6.2, which illustrates thethrust provided by the propulsion units when mounted in the helicopter. Fromfigure 6.2 a typical quadratic function can be obtained as equation 6.1 displays.By minimizing the background area of the helicopter, a larger thrust could beobtained, but still quite far from the thrust measured in the test rig. It shouldbe noted that an aerodynamically perfectly shaped helicopter was not expectedconsidering mechanical limitations and needs.

The propeller adapter was initially supposed to be made of Delrin plastic butafter consulting the personnel in the workshop it was decided that steel would bemore suitable mostly due to the threading. The steel adapter worked to satisfactionand did not affect the inertia substantially.

y = 7.9 10−8 x2 − 9.7 10−5 x (6.1)

6.1 Result 37

Speed in rpm

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Th

rust

in N

0

1

2

3

4

5

6Thrust as a function of speed

Thrust data

Quadratic

Figure 6.2: Plot showing the thrust obtained from the helicopter. The y valuedenotes the maximal thrust, 5.63 N for a given speed, 9000 rpm, x .

6.1.2 DiscussionThe results from the thesis are of interest for anyone who is interested in usingthe rig and develop a control system for it. The thesis can also provide adequateknowledge to anyone wishing to make a similar system, or in fact any kind of fixedpitch propulsion systems.

If the project was to proceed, an interesting aspect would be to test new pro-pellers with different shapes and number of blades. The system would probablybehave differently which would indeed be interesting to explore further.

6.1.3 Ethics & SocietyBuilding a mechatronic system, e.g. a helicopter rig, assumes responsibility. Bothethical and environmental.

Today’s society encounter all types of mechatronic systems. Fighter jets, mis-siles, etc. all are somehow based on a mechatronic system. From an ethicalperspective it should be mentioned that these weaponry systems are developedfor combat. Therefore policies about the responsibility when building this kind ofsystems should be provided for each concerned company.

From an environmental point of view there should be a plan for each companyhow to build the systems in the most environmental friendly way. There shouldalso, to some extent, be proactive work before building a product to minimize theimpact of the environment when the product is no longer working. For this partof the project, the motors of the rig could be important components to recycle dueto the risk of hazardous material spreading in the environment.

During this project the gender equality haven’t been a topic since it’s not rel-evant for this particular project. It is obvious that the project has been carriedthrough in a way that acknowledge both women’s and men’s abilities and devel-opments. Its been proven that both women and men are fully capable of working

38 Result, Analysis & Discussion

with the helicopter project regardless of sex.

Bibliography

[1] APC. APC propellers. http://www.apcprop.com/default.asp, 2015.

[2] R Archer. Introduction to aerospace propulsion. Prentice Hall, Upper SaddleRiver, N.J, 1996.

[3] Learn Engineering. Brushless DC Motor, How it works? http://www.learnengineering.org/2014/09/DC-motor-Working.html, 2012.

[4] David Greatrix. Powered flight the engineering of aerospace propulsion.Springer, London New York, 2012.

[5] Andreas Grönman. Compotech. URL:http://compotech.se/produkter/motorer/dc-motorer/, 2014.

[6] Klas Lindsten Marcus Almén. Design and implementation of a software andelectronics system for a 3DOF Helicopter. Technical report, 2015.

[7] Maxon. EC-max Ø40 mm, brushless, 120 W, Maxon motor. URL:http://www.maxonmotor.com/medias/sys_master/root/8813561643038/14-207-EN.pdf, 2014.

[8] University of Illinois. Airfoil Database. http://m-selig.ae.illinois.edu/ads/coord_database.html, 2015.

[9] Department of Industrial Electrical Engineering and IEA Automation. El-maskinsystem. Lund Institute of Technology, Lund, Sweden, 2000.

[10] Madaan Pushek. Brushless DC Motors – Part I: Construction and Oper-ating Principles. URL:http://www.edn.com/design/sensors/4406682/2/Brushless-DC-Motors-Construction-and-Operating-Principles, 2013.

[11] Clarence Silva. Mechatronics : an integrated approach. CRC Press, BocaRaton, 2005.

[12] John Brandt University of Illinois. Geometrical Data APC Thin Electric10x5. http://m-selig.ae.illinois.edu/props/data/apce_10x5_geom.txt, 2015.

[13] John Brandt University of Illinois. Propeller Database. http://m-selig.ae.illinois.edu/props/propDB.html, 2015.

39

40 Bibliography

[14] John Brandt University of Illinois. Static Data APC Thin Elec-tric 10x5. http://m-selig.ae.illinois.edu/props/data/apce_10x5_static_pg0819.txt, 2015.

[15] XFLR5. Airfoil software. http://www.xflr5.com/xflr5.htm, 2015.

Appendix A

Matlab Code

A.1 Matlab Code for the Database Calculations

1 % Clear a l l

3 rho = 1 . 2 2 5 ; %Density o f Air

5 prope l l e rd iam = 10 ; %Diameter o f p r o p e l l e r

7 A = dlmread ( ’ apce_10x5_static_pg0819 . txt ’ ) ; %P r o p e l l e r data from UIUC

9 D = prope l l e rd iam ∗ 0 . 0 2 5 4 ; %P r o p e l l e r diameter in i n c h e sRPM_data = A( : , 1 ) ;

11 CT_data = A( : , 2 ) ;CP_data = A( : , 3 ) ;

13

anta l =25;15

RPM = z e r o s (1 , anta l ) ;17 f o r i =1: anta l

i f i <= length (RPM_data)19 RPM( i ) = RPM_data( i ) ;

e l s e21 %Extrapo lat ion o f va lue s from o u t s i d e the g iven range

RPM( i ) = RPM_data( l ength (RPM_data) ) + ( RPM_data( l ength (RPM_data) ) − RPM_data( l ength (RPM_data) −1) ) ∗ ( i−l ength (RPM_data)) ;

23 endend

25

CT = z e r o s (1 , anta l ) ;27 f o r i =1: anta l

i f i <= length (CT_data)29 CT( i ) = CT_data( i ) ;

e l s e31 %Extrapo lat ion o f va lue s from o u t s i d e the g iven range

CT( i ) = CT_data( l ength (CT_data) ) + ( CT_data( l ength (CT_data) )− CT_data( l ength (CT_data) −1) ) ∗ ( i−l ength (CT_data) ) ;

33 end

41

42 Matlab Code

end35

CP = z e r o s (1 , anta l ) ;37 f o r i =1: anta l

i f i <= length (CP_data)39 CP( i ) = CP_data( i ) ;

e l s e41 %Extrapo lat ion o f va lue s from o u t s i d e the g iven range

CP( i ) = CP_data( l ength (CP_data) ) + ( CP_data( l ength (CP_data) )− CP_data( l ength (CP_data) −1) ) ∗ ( i−l ength (CP_data) ) ;

43 endend

45

n = RPM. / 6 0 ; %P r o p e l l e r v e l o c i t y in r e v o l u t i o n s per second .47

Thrust = rho ∗ CT . ∗ n .^2 ∗ D^4; %Thrust [N]49 Power = rho ∗ CP . ∗ n .^3 ∗ D^5; %Power [W]

Torque = Power . / ( 2 ∗ pi ∗RPM/60) ; %Torque [Nm]51

%P l o t t i n g53 f i g u r e ;

p l o t ( Torque ,RPM, ’ g ’ ) ;55 a x i s ( [ 0 0 .365 0 12000 ] ) ;

t i t l e ( ’ Torque vs RPM’ ) ;57 x l a b e l ( ’ Torque in Newton Meter ’ )

y l a b e l ( ’ Rotation Speed in RPM’ )59

f i g u r e ;61 p l o t ( Power ,RPM, ’ r ’ ) ;

a x i s ( [ 0 150 0 12000 ] ) ;63 t i t l e ( ’RPM vs Power ’ ) ;

x l a b e l ( ’ Power in Watt ’ )65 y l a b e l ( ’ Rotation Speed in RPM’ )

67 f i g u r e ;p l o t ( Thrust ,RPM, ’b ’ ) ;

69 a x i s ( [ 0 20 0 12000 ] ) ;t i t l e ( ’RPM vs Thrust ’ ) ;

71 x l a b e l ( ’ Thrust in Newton ’ )y l a b e l ( ’ Rotation Speed in RPM’ )

A.2 Matlab code for the Blade Element Theory

1 %APC Thin E l e c t r i c 10x5 p r o p e l l e r data

3 %Geometric datar_R = [ 0 . 1 5 0 0 .200 0 .250 0 .300 0 .350 0 .400 0 .450 0 .500 0 .550 0 .600

0 .650 0 .700 0 .750 0 .800 0 .850 0 .900 0 .950 1 . 0 0 0 ] ; %[ r /R]5 c_R = [ 0 . 1 3 0 0 .149 0 .173 0 .189 0 .197 0 .201 0 .200 0 .194 0 .186 0 .174

0 .160 0 .145 0 .128 0 .112 0 .096 0 .081 0 .061 0 . 0 4 1 ] ; %[ c/R]beta = [ 3 2 . 7 6 37 .19 33 .54 29 .25 25 .64 22 .54 20 .27 18 .46 17 .05 15 .97

14 .87 14 .09 13 .39 12 .84 12 .25 11 .37 10 .19 8 . 9 9 ] ; %[ degree s ]7

R = 5∗ 0 . 0 2 5 4 ; %Absolute r a d i u s [m]9 r = r_R ∗ R; %Distance along r a d i u s to geometr ic data p o i n t s . [m]

A.2 Matlab code for the Blade Element Theory 43

c = c_R ∗ R; %Chord length at r e s p e c t i v e geometr ic data p o i n t s . [m]11

rpm_max = 9000 ; %Estimated maximum rpm with a v a i l a b l e motors with ab i t o f an overe s t imate . [ rpm ]

13 v = (2 ∗ pi ∗rpm_max/60) . ∗ r ; %Air f low v e l o c i t y at the r e s p e c t i v e datap o in t s o f the p r o p e l l e r . [m/ s ]

15 kin_vis = 1.568 ∗10^−5; % Kinematic v i s c o s i t y o f a i r at roomtemperature . [ Pa∗ s ]

rho = 1 . 2 5 ; %Density o f a i r at room temperature . [ kg/m^3 ]17 r eyno lds = v . ∗c/ kin_vis ; %Reynolds number at the d i f f e r e n t geometr ic

data p o i n t s used f o r a n a l y s i s o f a i r f o i l in x f l r 5 .

19 %C o e f f i c i e n t o f l i f t and drag at r e s p e c t i v e geometr ic data po intalong the

%p r o p e l l e r r ad i u s . Found through a n a l y s i s o f a i r f o i l s f o r r e s p e c t i v ef low

21 %c o n d i t i o n s at each geomter ic data po int with x f l r 5 .%F i r s t 15 s t a t i o n s model led as a i r f o i l Eppler E63 and l a s t 3 as Clark

Y accord ing to in fo rmat ion from APC.23 Cl = [ 0 0 . 9 2 00 .90 00 .90 00 .90 00 .95 00 .97 01 .00 01 .05 01 .15 01 .17

01 .17 01 .17 01 .17 01 .17 01 .16 01 .26 01 .25 0 1 . 2 4 ] ; %C o e f f i c i e n t o fl i f t

Cd = [ 0 0 . 5 5 00 .70 00 .60 00 .50 00 .40 00 .30 00 .30 00 .30 00 .29 00 .2700 .24 00 .22 00 .20 00 .20 00 .175 0 .040 0 .030 0 . 0 3 0 ] ; %C o e f f i c i e n to f drag

25

%Creat ing s t a t i o n s averag ing the va lue s between adjacent geometr icdata p o i n t s a long the p r o p e l l e r r ad i u s .

27 l = z e r o s (17) ;A = z e r o s (17) ;

29 Clavg = z e r o s (17) ;Cdavg = z e r o s (17) ;

31 vavg = z e r o s (17) ;f o r i =1:17

33 l ( i ) = ( r ( i +1)+r ( i ) ) /2 ; %Distance to midpoint o f each r a d i a ls t a t i o n . Used f o r c a l c u l a t i n g torque c o n t r i b u t i o n from eachr a d i a l s t a t i o n .A( i ) = ( r ( i +1)−r ( i ) ) ∗ ( ( c ( i +1)+c ( i ) ) /2) ; %Planform area at eachr a d i a l s t a t i o n .

35 Clavg ( i ) = ( Cl ( i +1)+Cl ( i ) ) /2 ; %C o e f f i c i e n t o f l i f t f o r eachr a d i a l s t a t i o n .Cdavg ( i ) =(Cd( i +1)+Cd( i ) ) /2 ; %C o e f f i c i e n t o f drag f o r each r a d i a l

s t a t i o n .37 vavg ( i ) = ( v ( i +1)+v ( i ) ) /2 ; %Air f low v e l o c i t y at each r a d i a l

s t a t i o n .end

39

%P r e a l l o c a t i o n f o r each r a d i a l s t a t i o n as w e l l as blade sums .41 Fl = z e r o s (17) ;

Fd = z e r o s (17) ;43 T = z e r o s (17) ;

FliftTOT = 0 ;45 TorqueTOT = 0 ;

47 f o r i =1:17Fl ( i ) = 0 .5 ∗ rho ∗Clavg ( i ) ∗A( i ) ∗vavg ( i ) ^2 ; %Thrust generated byeach r a d i a l s t a t i o n at max_rpm .

44 Matlab Code

49 Fd( i ) = 0 .5 ∗ rho ∗Cdavg ( i ) ∗A( i ) ∗vavg ( i ) ^2 ; %Drag induced at eachr a d i a l s t a t i o n at max_rpm .T( i ) = Fd( i ) ∗ l ( i ) ; %Torque r e q u i r e d by each r a d i a l s t a t i o n atmax_rpm .

51

TorqueTOT = TorqueTOT + T( i ) ; %Total torque r e q u i r e d per blade atmax_rpm .

53 FliftTOT = FliftTOT + Fl ( i ) ; %Total t h r u s t generated per blade atmax_rpm .

end55

TorqueTOT = 2∗TorqueTOT %Total torque r e q u i r e d per p r o p e l l e r to keepmax_rpm . Note that we have 2 b lades per p r o p e l l e r .

57 FliftTOT = 2∗FliftTOT %Total t h r u s t generated per p r o p e l l e r atmax_rpm . Note that we have 2 b lades per p r o p e l l e r .