2002 SAE Mini Baja

1
2002 SAE Mini Baja

• Johanna Gustafsson, drive train
• Shaun Chin, front suspension
• Andre Susanto, rear suspension
• Andrew Criss, frame / controls
• Joe Emery, front suspension
• Mike deSousa, frame/controls
• Gus Mares, drive train
• Justin Zimmerman

2
Front Suspension

• Chosen design
• Short Long Arm with a 10-20 degree rake angle
• Advantages
• Minimal geometry change
• Rake angle helps with large bumps
• Easy to include adjustability
• Disadvantages
• Tight space
• Rake angle reduces effective vertical travel
• Alternative designs considered
• Symmetrical A or H arms
• McPherson struts
• Chapman struts

3
Front Suspension (Steering)

• Considerations
• Ackerman geometry
• Protecting steering arms or design it for impact
• Yoke and rod
• Rack and pinion
• Pitman arm
• Transferred road forces to steering wheel
• Shape and size of steering wheel
• Questions
• Effects of reverse Ackerman
• Effects of front suspension geometry on bump
  steer

4
Frame Design

• Materials being considered
• 4130 Chromoly
• 6061-T6 Aluminum
• Advantages

Disadvantages
5
Frame Design

• Considerations
• Minimizing frame members
• Use more curved members
• Design frame around suspension and drive train
  requirements
• As close to space frame as possible
• FEA analysis
• Testing with seismic vertical force table
• Enclose engine and drive train

6
Drive Train (Transmission)

• Choices
• CVT only with a chain final reduction
• CVT with gear box (reverse) with a chain final
  reduction
• Gear box only (reverse) with a chain final
  reduction
• Negative considerations
• CVT has low efficiency (up to 92 under idealized
  conditions)
• Gear box requires more input from driver
• CVT is difficult to tune to get max efficiency
• CVT is difficult to predict for design purposes
• Positive considerations
• CVT is easy to drive
• CVT is forgiving of terrain changes with little
  input from driver
• Gear box gives more precise control of vehicle
• Gear box provides reverse

7
Drive train (drive shaft)

• Choices
• CV joint from a high suspension travel ATV
• CV joint from a small automobile
• Vehicles being looked at
• Ford Escape
• Honda CR-V
• Toyota RAV-4
• Geo Metro
• Kia Sportage
• Geo Tracker
• Considerations
• Protecting the drive shaft from impact damage
  (skid plate)
• or
• Designing the drive shaft to survive impact damage

8
Rear Suspension

• Chosen design
• Adjustable trailing arm and control arm
  combination
• Advantages
• Large suspension travel
• Minimal geometry change
• Very adjustable
• Plenty of room for shock mounts and drive shaft
• Disadvantages
• Under current design, trailing arm is exposed to
  road hazard
• If any of the arms are bent, theres danger of
  drive train failure
• Alternative designs considered
• Trailing arm only
• Semi trailing arm
• A arms
• McPherson/Chapman struts

9
Miscellaneous Issues

• Should we use a differential?
• If not, how would that affect the handling?
• Can we compensate by having enough weight
  transfer on corners?
• Where should the roll center be?
• Where should the CG be?
• How would the car behave when we jump it?
• What should be the max speed?
• Can acceleration loss by using bigger tires be
  compensated by increasing the gear ratio?
• At what tire angle should we design perfect
  Ackerman at?
• What is the largest dynamic force experienced by
  the frame?
• Is it small enough that aluminums minimal
  fatigue resistance matters very little?