SAE – HANDS-ON EXPERIENCE

MILAD PARVIZI

Abstract

The SAE Collegiate Design Series, organized and supervised SAE International, gives students from

around the globe the opportunity to apply their newly gained theoretical knowledge in solving real world

problems. The competitive nature of the series sets high standards which are comparable to ones set by

various racing series such as Formula 1 and Dakar Rally. Most importantly, these competitions gave me

my first real taste for Motorsport, and I love it!

As an undergraduate engineering student involved in the Concordia chapter of SAE International, I have

had the opportunity to work on multiple projects with some of the most incredible undergraduate

students. In 2012 I assembled and led a team of first and second year students with minimal Baja SAE

experience to redesign, and race CBR12 at the 2012 Wisconsin Baja competition. We managed to finish

the race despite the multiple setbacks.

The following year, I joined the Formula SAE Racing and was tasked with redesigning the Drivetrain

system for CFR13. This particular system had always been neglected due to the lack of manpower. I

decided to upgrade the differential unit, re-examine the loading condition for each component, and redo

all performance and stress calculations. Over the 2012-2013 season my teammate and I completely

redesigned the system with our focus on reliability and serviceability. Having completed a season with

just a few minor problems, I decided to optimize the system. Thus, I assembled a new team of final year

students to undertake the project for the 2013-2014 season. The results were a 24.16% weight reduction,

and 6.65% performance improvement in acceleration and skidpad runs.

Table of Figures

Figure 1: CBR12 at Baja Wisconsin_______________________________________________________________ 5

Figure 2: CBR12 Drivetrain with mounting plate ____________________________________________________ 6

Figure 3: CFR14 at Michigan International Speedway ________________________________________________ 8

Figure 4: Quaife Differential, CFR10 _____________________________________________________________ 9

Figure 5: Torsen Differential, CFR12 _____________________________________________________________ 9

Figure 6: Drexler Differential FSAE ______________________________________________________________ 9

Figure 7: Engine Torque Curve - Dyno Run _______________________________________________________ 12

Figure 8: RCV stock half shaft. 4340 Steel, 53 C Rockwell hardness with .5 in inner bore ____________________ 12

Figure 9: Sprocket Adaptor,7075-T81 Aluminum alloy – As manufactured _______________________________ 13

Figure 10: The modular design on the sprocket/sprocket adapter to enable Final Drive ratio tuning ___________ 13

Figure 11: CFR13 Drivetrain at FSAE Lincoln 2013 ________________________________________________ 14

Figure 12: Theoretical Shift Points for 3.63 Final Drive ratio _________________________________________ 16

Figure 13: CFR14 Acceleration time with respect to similar teams _____________________________________ 17

Figure 14:CFR14 Skidpad time with respect to similar teams __________________________________________ 18

Figure 15: CFR14 AutoCross time with respect to similar teams _______________________________________ 18

SAE Collegiate Design Series Overview

Each year many SAE competitions are held around the world. These competitions give student the

opportunity to apply their knowledge in designing, building, and racing different vehicles in international

competitions. Moreover, each team is responsible for securing funding for the project, managing task

forces and schedules, and meeting competition deadlines.

Each SAE competition consists of 3 events:

Technical Inspection: Each competition has its own rule book which the competing teams

must adhere to. These rules dictate everything from the design of the vehicles (safety features

only) to the competition rules and events. Each vehicle is checked thoroughly at Technical

Inspection to ensure it has met all the rules. The team are required to submit calculations and

other documents as requested.

Static Events: The static events include: Cost Report, Design Report, Cost Presentation,

Marketing Presentation, and Design Presentation. All of the reports need to be submitted

before the actual competition date, and are judged by volunteers from industry leading

companies such as: GM, Ford, Honda, Bosch, Toyota, Continental Tires, Mahle, Magna

Powertrain, and other reputable companies. Similarly, the presentations are also judged by

high ranking engineers from the above mentioned companies.

Dynamic Events: Although the dynamic events for each competition are different, they are all

designed to test the vehicle’s performance. During these events the cars are testing to their

limits. The dynamic events conclude with an endurance test of some sort to test the reliability

and durability of each car.

Each SAE competition presents a highly competitive environment in which each team is pushed to its

limits. The diversity of the participating teams, based on their geographical locations, and the amount of

support they receive from their sponsors, gives the involved students the real image of what it would be

like to work in highly competitive industries.

Team Coordinator – CBR12

Baja SAE is an international competition where more than 141 teams from around the globe come to

compete in a 3-day long competition. In an attempt to level the playing field, each team is given the same

engine, a single cylinder 305cc Briggs Stratton. The goal of the competition is to design, build, and race

an off-road vehicle that can withstand the harshest element of rough trains [1].

CBR11 was designed and built with a team of experienced Baja members whom had decided to undertake

the project as their Capstone Engineering Design Project1. CBR11 ranked in the top third of all the

competitions it participated in.

Figure 1: CBR12 at Baja Wisconsin

I joined the team in sept 2010 and was tasked with securing financial support for the project. Over the

next 4 months I sent out over 20 sponsorship packages raising $1500 in cash funding.

In January 2012 I joined the design team and was tasked with designing and fabricating Kill Switch

Brackets for the vehicle, as well as analysing each subassembly for possible weight reduction. As the

competition approached I started to shadow the team captain assisting him in pre-run preparations, and

also in preparing technical documents required by organizing committee. At the end of the season I was

voted the coordinator for the coming season.

The new season was the start of the new challenges. Aware of the challenges ahead, and with a game plan

for the year, my team and I started trouble shooting and redesigning the vehicle’s gearbox and rear

suspension.

1 The Capstone Engineering Design project is a supervised design, simulation or experimental project involving the definition of a

design problem, carrying out the research and design, and demonstrating results. [1]

Problem:

The main issue in the 2010-2011 season was the planetary gearbox. While compact and efficient in

design, it was not reliable. The gearbox had a forward and a reverse gear. The shifter fork would

repeatedly break/jam and this required disassembly of the entire gearbox.

The rear suspension was a trailing arm setup with 2 lateral links to adjust chamber and toe. We bent

multiple trailing arms.

Lastly, the team had no Data acquisition, and hence we were not able to validate our designs.

Figure 2: CBR12 Drivetrain with mounting plate

Goals and Objective:

The goal was to match our previous ranking, at the very least.

The objectives were set as:

Redesign the shifter fork and the gearbox housing to prevent extensive flex in the shifter fork,

and also to make for smoother gear changes.

Redesign the rear suspension to prevent bending of the trailing arms, while keeping the same rear

track, and wheelbase.

Purchase / make a Data Acquisition system

Method and Calculations:

The entire drivetrain system was modeled in Solidworks and we ran FEA analysis on the input shaft,

output shaft, and various shifter fork designs. The team experimented with multiple gearbox housings as

well.

The rear suspension was redesigned in Lotus suspension software. The mounting points for the rear

suspension were relocated, including the shock mounting points which required some frame

modifications.

Results:

After having redesigned the drivetrain and the rear suspension, the car was tested for reliability. Though

the rear suspension performed satisfactory, the shifter fork and the shifting mechanism continued to be

problematic. It was decided to “lock” the gearbox in the “forward gear” using an ABS plastic2 spacer.

CBR12 met all the competition deadlines, and passed technical inspection. The team surpassed

expectation at the Design presentation.

CBR12 completed 3 out of 4 dynamic events. At the endurance race the gearbox jammed just after the

first hour. The car was pulled of the track. The problem was a leak in the gearbox which resulted in the

ABS plastic melting and damaging the bearings. The team worked restlessly for 75 minutes to clean the

gearbox and replace the bearing. CBR12 was sent back out and didn’t return until last 5 minutes of the

race at which point the car lost its brakes due to a damaged front right brake caliper.

The team did not meet the goal of matching its previous ranking, but it learned from its failures and has

been improving since. We also managed to reach an agreement with ISAAC Instruments to secure an

Isaac Box which has been helping the team validate its designs ever since.

2 This was the only material available in the shop at the time.

Drivetrain Design Lead – CFR13 & CFR14

Figure 3: CFR14 at Michigan International Speedway

Formula SAE is perhaps the most prestigious SAE event. The concept behind Formula SAE is that a

company has contracted a team of students to design and build a single sitter – open wheel formula style

vehicle for the non-professional weekend racer. The prototype is evaluated on its potential to be

manufactured and marketed. Each team designs, builds, testes their prototype based on a series of rules

ensuring on-track safety and clever problem solving [2].

The rules of Formula SAE are much less strict allowing students to think out of the box. This enhances

the comparative nature of the series and puts extra pressure on the team to explore any and all options in

any subsystem to gain the competitive edge.

The Drivetrain system in a vehicle is responsible for transmitting the power and torque from the engine to

the driving wheels granting the driver access to the engine torque and power at various driving speeds.

Having said this, the drivetrain system in a racing vehicle is many time more complicated even though, in

looks at least, it is similar to an ordinary Drivetrain system.

When designing components for a racing vehicle it is absolutely necessary to optimize its design to as

near to perfect as one’s resources permit. This requires hours of calculations, simulations, and testing to

ensure the final product is not only as light as possible, but also strong enough to endure the stresses for

the period of time required. With this in mind, I decided to set simplicity in design and overall

adjustability/serviceability as the two main criteria for the design of each component.

CFR13

Problem:

Pictures below are the 2 previous Drivetrain systems on the CFR vehicles.

Figure 4: Quaife Differential, CFR10

Figure 5: Torsen Differential, CFR12

The two previous drivetrain systems were overdesigned as the components were simply bought from

various aftermarket suppliers and assembled. The components were designed for bigger and more

powerful vehicles. Furthermore, the team ran mechanical limited slip differentials which, while

performed the tasks, were heavy and not easily adjustable. I decided to change the differential for a clutch

type limited slip differential in attempt to save weight and enhance adjustability. After much research I

decided to purchase a Drexler Limited Slip Differential since it is just over half the weight of ordinary

mechanical slip differential, offers 3 set ups, and its configurations can be changed in the pits.

Figure 6: Drexler Differential FSAE

Goals and Objectives:

The goal was to reduce weight, and improve the vehicles performance.

The Objectives were set as:

Weight reduction

Improve Adjustability/ serviceability

Improve performance

Method and Calculation:

Before starting the design process my teammate and I reviewed the data available from our previous

competitions and concluded that our vehicles have rarely reached the 100km/h speed mark. We also

consulted with our faculty advisor and other veterans in Formula SAE series and concluded that the

FSAE competitions are designed to test a vehicles handling and not its top speed. Thus, it proves

beneficial for us to focus on acceleration rather than top speed. As a result, we eliminated the 5th and 6

th

gear in the gearbox and increased final drive. The tables below summarize the changes.

CFR13

Gear Gear Ratios

Primary Reduction 1.822

1st 2.833

2nd

2.063

3rd

1.647

4th

1.421

5th

1.273

6th

1.174

Final Drive 3.636

CFR12

Gear Gear Ratios

Primary Reduction 1.822

1st 2.833

2nd 2.063

3rd 1.647

4th 1.421

5th 1.273

6th 1.174

Final Drive 3.273

Eliminating the 5th and 6

th gears resulted in 36.34 % inertia reduction in the gearbox.

Due to the lack of data, proper instruments, and the availability of different size engine and Final drive

sprockets, I decided to set the final gear ratio experimentally. The table below summarizes the possible

gear ratios.

Final Sprocket

Engine

Sprocket

36 40 43

9 4.00 4.44 4.78

11 3.27 3.64 3.91

13 2.77 3.08 3.31

3.27 and 3.64 ratios were chosen experimentally during testing.

Next, we focused on calculating the theoretical force each component would experience under Worst

Condition. The Worst Conditions was defined as:

Max available torque from the engine ( 58.3 N.m @ 7600 RPM)

Max tractive force from the tires

Engaging 1st gear, and highest Final Drive ratio (3.64)

Figure 7: Engine Torque Curve - Dyno Run

Max force and torque applied to each component was determined using the Worst Condition criterion.

Below are images of the sprocket adapter and a half shaft during the FEA optimization process.

Figure 8: RCV stock half shaft. 4340 Steel, 53 C Rockwell hardness with .5 in inner bore

Engine Torque Curve - Dyno Run

0

10

20

30

40

50

60

70

0 2000 4000 6000 8000 10000 12000 14000

Engine RPM

To

rqu

e [

N.m

]

Figure 9: Sprocket Adaptor,7075-T81 Aluminum alloy – As manufactured

Using the Engine data provided, we also developed graphs showing the torque at the wheel for each gear

and Final Drive ratio, giving our driver and vehicle’s dynamics lead a better idea of the vehicle’s

characteristics in the corners, and our driver an optimal RPM range for each gear.

Having done no performance calculations, it was decided to improve adjustability so that the Final Drive

ratios could be changed on the track. Thus, it was decided to add one more component, the sprocket

adapter, to enable quick changing of the Final Drive sprocket. This proved extremely beneficial at testing.

Figure 10: The modular design on the sprocket/sprocket adapter to enable Final Drive ratio tuning

Results:

The picture below is of the final product, taken at the 2013 Formula SAE Lincoln competition.

Figure 11: CFR13 Drivetrain at FSAE Lincoln 2013

CFR13 became the first car to finish the endurance race in its first SAE competition in the history of the

team, and ranked 21st overall in Lincoln, giving the team its best finish in its recent history.

Powertrain took the highest score in the design presentations, matching for 2nd

in the category.

CFR14 Back from the competition and armed with new knowledge, I set out to optimize the system. For this, I

assembled a team of final year Mechanical Engineering students, and decided to undertake this project as

our Capstone project.

Goals and Objectives:

The team set the goal as: Giving CFR14 the best drivetrain possible.

The objectives were set as:

Weight Reduction by 20%

Performance improvement by 5%

Method and Calculation:

There were only a few minor problems with the system during the 2012-2013 season. Thus, I decided to

divide my team into 2 task forces, one to focus on weight reduction, and other to focus on performance

improvement. Furthermore, in an attempt to reduce cost, we decided to purchase and modify components,

rather than manufacturing from scratch. Not only this strategy proved to be cost efficient, it also halved

the manufacturing resources we required.

Theoretical Performance calculations were carried out by employing the formula below:

𝑎 =𝜏𝐸 𝐺

𝑚𝑅

Where:

G = Overall gear reduction

m = Vehicle’s mass (including Driver)

R = Effective Tire Radius

𝜏 = Engine Torque

As it can be observed from the formula, reducing tire size would increase acceleration, but that would

have required suspension modifications which would not be possible.

From the above formula, we were able to determine shift point (RPM) for each gear, and better compare

and optimize the Final Drive ratios. The tables below summarize the calculations.

Final Drive Reductions (Engine Sprocket/ Final Drive

Sprocket)

3.27 (11/36) 3.63(11/40)

Max Acc. in 1st Gear [a/g] 1.74 1.94

Top Speed – 1st Gear [Km/h] 69.7 62.7

Top Speed – 2nd

Gear [Km/h] 95.75 86.18 Top Speed – 3

rd Gear [Km/h] 119.9 107.9

Top Speed – 4th

Gear [Km/h] 138.9 125.1 Shift Points [Engine RPM]

1st Gear 12000 (Rev Limiter) 12000 (Rev Limiter)

2nd

Gear 11900 11850 3

rd Gear 11400 11300

Figure 12: Theoretical Shift Points for 3.63 Final Drive ratio

In an attempt to move away from the theoretical calculations, and better defining the forces in the system,

the team decided to utilize a different approach. A compiled g-to-g diagram from all the testing sessions

in the summer was created and the maximum longitudinal acceleration was measured to be 0.8g’s. From

this the torque applied at the wheels was calculated to be 445.57, and rounded up to 500N.m.

Theoratical Shift Points - 3.63 Final Reduction

0

0.5

1

1.5

2

2.5

0 20 40 60 80 100 120 140

Vehicle Speed [km/h]

Accele

rati

on

[a/g

]

1st Gear

2nd Gear

3rd Gear

4th Gear

Moreover, I created a “similar vehicle” category to be able to better compare the performance

improvements of the vehicle.

The Similar vehicle category was defined as:

Use a 4 cylinder Engine

Engine Displacement must be 600cc

Car weight should be 480 lbs (+/- 10 lbs)

8 teams met the above mentioned requirement. They are:

Car Number University 1 University of Kansas – Lawrence 6 Michigan State University 21 University of British Columbia 39 California State University – Fullerton 48 University of Southern California 79 University of Illinois – Urbana 80 Queen’s University – Ontario, Canada 85 Colorado State University

The graphs below summarize the 2013 results, comparing CFR times with the other 8 teams.

Figure 13: CFR14 Acceleration time with respect to similar teams

Figure 14:CFR14 Skidpad time with respect to similar teams

Figure 15: CFR14 AutoCross time with respect to similar teams

Results:

CFR14 proved to be the best Drivetrain system designed by the Concordia Formula Racing team. The

team met, and exceeded all expectations. We achieved a weight reduction of 24.16% (4.11 lbs), and

performance improvement of 6.65%. The table below summarizes the weight reduction achieved.

Component Old

Design

New

Design

Weight

Reduction

Percent

Weight

Reduction

Half Shafts

17.75" 1.7 0.99 0.71 41.76

14" 1.4 0.84 0.56 40

Diff Carriers

Chain Side 1 0.6 0.4 40

Not Chain Side 0.8 0.5 0.3 37.5

Sprocket 0.9 0.45 0.45 50.00

Sprocket

Adapter 0.6 0.3 0.3 50

Chain 2.91 1.52 1.39 47.77

Jacking Point

Bar 0.5 0.5 0 0

Drexler 5.6 5.6 0 0

Tripods 1.6 1.6 0 0

Total 17.01 12.9 4.11 24.16

CFR14 competed in the 2014 Formula SAE Michigan in May 2014, and although it did not rank well in

dynamics events due to a faulty steering rack and brake caliper, it placed 15th out of 126 in the Design

event, the best in Concordia history.

Included in this document you will also find the 2014 Drivetrain Handout.

Bibliography

[1] "Student SAE International," SAE International , [Online]. Available:

http://students.sae.org/cds/bajasae/about.htm. [Accessed 24 Feb 2015].

[2] "Formula SAE Serie," SAE International , [Online]. Available:

http://students.sae.org/cds/formulaseries/about.htm. [Accessed 24 Feb 2015].

[3] "Department of Mechanical and Industrial Engineering - Concordia University," [Online]. Available:

http://www.concordia.ca/encs/mechanical-industrial/students/undergraduate/capstone.html. [Accessed

21 February 2015].

DRIVETRAINThe team concentrated on aspects such as weight reduction and reliability as the main design focus, while also being conscious of cost efficiency and manufacturability. Static and dynamic analysis was performed in order to optimize the physical design and performance. The new design exceeds the original goal of 20% reduction in weight for the same lifecycle of the previous design.

INTRODUCTION .

• Reduce total weight by 20%• Design for a life span of 10,000 lifecycles• Transfer torque from engine to the wheel• Differentiate wheel speed• Jacking point for the vehicle

. OBJECTIVES

CFR2014 sprocket

CFR2014 drivetrain section view

. RESULTS

CONCLUSION .Weight reduction achieved is of 24.16%. The sprocket is capable of withstanding three times the loading it will foresee without any plastic deformation taking place. Through tests conducted with the aid of computer simulation software, the team arrived at two optimal setups as far as gear ratios are concerned. A gear ratio of 3.6 would deliver a better performance, obtained from a 11-36 or 11-40 pinion and sprocket combination. In addition, 4340 steel half shafts of hardness Rockwell C 53, with a bore diameter 5/8”. Further validation is required, for example, the validation of differential carriers, as well as the half shafts.

CFR2014 sprocket adapter FEA