1. SAE Mini Baja: Powertrain
By: Chris Gilson & Spencer Suggs
Advisor: Ho-hoon Lee
Instructor: Cris Koutsougeras
ET493

3. What is Mini-baja?
The SAE mini-baja is an international collegiate engineering challenge to design and build an off-road vehicle
This vehicle will go through various stress tests:
Acceleration
Off-road terrain
Steep incline
Endurance

4. powertrain
The Powertrain is the mechanisms that transmit the driving force from the engine of a vehicle to its axles
Includes:
Engine
Continuously Variable Transmission (CVT)
Differential

5. Engine Model: Briggs & Stratton 10HP OHV Intek Cost: $250.00
Max Power Output: 10HP
Max Torque Output: 14.5 ft.lbs.

6. Engine Mount design Designed for easy removal & maintenance
Material: T Aluminum
Dimensions:
9” Length
8.37” Frame Rail Span
1” Thickness

7. Engine mount stress analysis
Σ 𝑀 𝐴 =−wa−Fb+2a 𝑅 𝐵 =0
𝑅 𝐵 = 𝐹 𝐵 +𝑤𝑎 2𝑎 = 𝐹 𝐵 2𝑎 + 𝑤 2
𝑅 𝐵 = ∗
𝑅 𝐵 =
𝑅 𝐵 = 𝑁
Σ 𝑀 𝐵 =𝑤𝑎−𝐹𝑏+2𝑎 𝑅 𝐴 =0
𝑅 𝐴 = 𝐹 𝐵 −𝑤𝑎 2𝑎 = 𝐹 𝐵 2𝑎 − 𝑤 2
𝑅 𝐴 = ∗.0975 −
𝑅 𝐴 = −137.8
𝑅 𝐴 = −29.1 𝑁
Max Torque from engine is 14.5 ft. lbs. = 19.7 Nm
Torque = F * distance
F = N
W = m * g
W = N

8. Force equilibrium +↑ΣFy=0 RA+RB+29.1−246.5=0 RA+RB +29.1−246.5=0
RA+RB =217.4N
+↺ΣMA=0
RB (0.225)+(29.1)(0.015)-(246.5)(0.21)=0
RB (0.225)+(29.1)(0.015)-( 246.5)(0.21)=0
RB= N
RA+RB=217.4
RA =217.4
RA =−10.727N

9. Shear force diagram 0≤x≤0.015: +↑ΣFy=0 −10.727−V1=0 V=−10.727 N
0.015≤x≤0.21:
 +↑ΣFy=0
− −V=0
V= N
0.21≤x≤0.225:
− −246.5−V=0
V=− N

10. Bending moment diagram
0≤x≤0.015: 
+↺ΣMb=0
−10.727x−Mb=0
Mb=−10.727x Nm
0.015≤x≤0.21: 
−10.727x+(29.1)(x−0.015) −Mb=0
Mb=18.373x−0.436 Nm
0.21≤x≤0.225: 
+↺ΣMx=0
−10.727x+(29.1)(x−0.015)+(−246.5)(x−0.21)−Mb=0
Mb=− x Nm

11. Solidworks stress simulation
T Aluminum yield strength = 2.75e8 N/m2
Largest concentration of stress = 1.102e5 N/m2
Material will not fail under load

12. CVT Transmission
The continuously variable transmission is an automatic transmission that can change seamlessly through a range of speed ratios
Commonly used in ATV / off-road utility vehicles

13. CVT Model: COMET 780 Price: $250.00 Specs:
High Speed Ratio ( 𝑅 𝐻 ) = 3.71 : 1
Low Speed Ratio ( 𝑅 𝐿 ) = .69 : 1
CVT Efficiency (NCVT) = 88%
Gear Reduction Ratio (RG) = : 1
RPM-Engage : The RPM at which the CVT first engages = 800 rpm
RPM-Range : Highest rpm – idle rpm = 2800 rpm

14. Differential Selection
Independent Rear Suspension (IRS)
PROS:
Greater suspension travel
Better ride quality
Greater cornering performance
Higher ground clearance
CONS:
Less power transfer
Higher cost
Higher chance of mechanical failure

15. Differential Model: Dana Spicer H-12 FNR Price: $500 - $800 Specs:
Load Rating: 1500 lbs.
Input Torque Rating: 24 ft. lbs. continuous
Max Torque Rating: 96 ft. lbs. intermittent
Gear Ratio: : 1

16. Differential mount Designed for easy removal & maintenance
Material: T Aluminum
Dimensions:
12” height
10” length
.25” thickness
4” axle hole

17. Mounting bracket material selection
Material: T Aluminum
Tensile Strength: 290 Mpa (42,000 psi)
Yield Strength: 240 Mpa (35,000 psi)
Weight: .098 lb./c.u. in.

18. Bolt grade selection Engine bolt size = .375 m Max Concentration Force
Doubled for Safety Factor
= 500 N
Max Shear Force = 228 N
= 480 N
Selection using graph: SAE Grade 5
Tension Cap. = N
Shear Cap. = N

19. Torque transferred to wheels
RPM
CVT Ratio (RCVT)
Complete Ratio (RC)
Engine Output Torque (ft. lbs)
Torque at the Wheels
(ft. lbs)
1800
2.63 : 1
29.11 : 1 13
336
2800
1.66 : 1
18.37 : 1
14.5
235
3600
.69 : 1
7.64 : 1
13.8 98

20. Powertrain Positioning
Simplistic Design
Easy Installation
Painless Maintenance
45 Degree belt angle
Decreases belt length
Smaller wheel base length

21. Going forwrd Begin to order parts needed Machine parts to spec
Begin Assembly
Test