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BAJA SAE Brakes and Steering
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BAJA SAE Brakes and Steering
Matthew Armstrong
What is BAJA SAE?
Introduction
The Society of Automotive Engineers (SAE) run design competitions where students get to design and build a fully functional off-road vehicle and compete against each other.
Specifications
Fasteners: Must be made captive
Braking System: All wheels must fully lock and pedal must withstand 450 lb
Steering System: Must not pinch brake lines. Must not entangle drivers clothing
Camber: the angle between a tilted wheel plane and the vertical
Fully Locked: When the brakes are applied, and the tires do not spin.
Key Definitions
Design
Braking System
- Must be activated by a foot pedal
- Will include the following components
- Brake calipers
- Master cylinders
- Brake rotors
- Brake pedal
- Caliper Mount
Steering System
- Required for all Baja SAE events to turn the vehicles left to right
- Will include the following components
- Steering wheel
- Steering mount
- Steering Shaft
- Rack and pinion
- Hubs
- Tie rod sleeve
- Tie rod ends
Braking System
Includes: caliper selection, master cylinder selection, design of mount for caliper, brake pedal and mount
Steering System
Analysis
Includes: rack and pinion selection, tie rods, steering shaft, steering mount, hubs, and steering wheel
Force Analysis
Braking
Combined Loading at Point C: n=9.5
Tearout at A: n=5.2, n=24
Tearout at B: n=2.3, n=18.6
Largest Bending Moment Normal: n=27
Largest Bending Moment Combined: n=15.4
Strength Analysis
All safety factors > 1, therefore part will not yield and meets SAE requirements.
Forces were checked throughout the following locations within the system:
Steering hub, steering shaft, steering mount, and tie rods
Steering
Force Analysis
F1= 12.5 lb
T1=75 in*lb
F2=66.6 lb
Steering Hub
All safety factors > 2, therefore part will not yield and meets SAE requirements.
Strength Analysis
Steering Link Connection
Tensile tearout: n=2,056
Shear tearout: n=232
Normal Stress: n=30
Combined loading: n=274
Lower Control Arm Tab:
Tensile tearout: n=86
Shear tearout: n=14
Normal stress: n=15
Combined loading: n=23
Upper Control Arm Tab
Tensile tearout: n=149
Shear tearout: n=24
Normal stress: n=5.95
Combined loading: n=16
Force Analysis
Steering Shaft
Strength Analysis
Combined Loading: n=29
Transverse Shear: n=152
All safety factors > 2, therefore part will not yield and meets SAE requirements.
Force Analysis
Steering Mount
Normal stress: n=45
Combined loading: n=238
All safety factors > 2, therefore part will not yield and meets SAE requirements.
Strength Analysis
Strength Analysis
Tie Rods
Shear on threads: n=145
All safety factors > 2, therefore part will not yield and meets SAE requirements.
Force Analysis
Pins/Bolts
Steering Connection Pin A
Pin B Pin C
Strength Analysis
Shear Stress: n=84
Steering Connection
All safety factors > 1, therefore part will not yield and meets SAE requirements.
Strength Analysis
Shear stress: n=3
Pin A
All safety factors > 1, therefore part will not yield and meets SAE requirements.
Strength Analysis
Pin B
Shear stress: n=1.03
*Note: usually a part with a safety factor less than 2.0 would not get accepted as being safe, however, these stresses are when the brake pedal is fully compressed and assuming the driver is applying 450 lb of force as specified by SAE. The force specified from SAE is highly unrealistic for most drivers to reach.
All safety factors > 1, therefore part will not yield and meets SAE requirements.
Strength Analysis
Shear stress: n=225
Pin C
All safety factors > 1, therefore part will not yield and meets SAE requirements.
What Does it All Mean?
Costing
Conclusions
- All safety factors are greater than the minimum required safety factor
- Pins/Bolts will yield first before expensive components
- Most difficult part to analyze: Brake Pedal
- Both systems meet all SAE standards and are race eligible
*Minimum Required Safety Factors
"n" must be greater than 2, unless one of the following:
- Brake Pedal
- Bolt/Pin
Recommendations
If there had been more time, the report also would have included the following:
- Routing for brake lines
- ANSYS
- Brake light wiring
- Redesign of parts with very high safety factor
Time Summary
Total Time: 278.5 hours
Equal to:
- 69.625 Midnight Mayhem SAE races
- 92.83 NASCAR Races
- Driving from Conestoga College to Midnight Mayhem 30.94 times