2. 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.
3. 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
4. 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.
5. 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]
6. 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
7. 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.
8. 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.
9. 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
10. 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 6th
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
11. 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 6th
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.
12. 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
Torque[N.m]
13. 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
14. 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.
15. 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 =
𝜏 𝐸 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.
16. 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 – 3rd
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
3rd
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]
Acceleration[a/g]
1st Gear
2nd Gear
3rd Gear
4th Gear
17. 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
18. Figure 14:CFR14 Skidpad time with respect to similar teams
Figure 15: CFR14 AutoCross time with respect to similar teams
19. 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
20. 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].
21. DRIVETRAIN
The 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
22. . 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
