The GVSU Baja Race Team

1
The GVSU Baja
Race Team

• Front Suspension Redesign

Michael R. Olson Michael R. Mulder Paul
Wittkoski Jeremy Pruneau Andrew Tallman Ryan E.
Peer
Jeff A. Blair Dan J. Schwarz Ryan J.
Anderson Chris Dittmer Kevin Mattox Bryan C.
Keefe
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Objectives
Improve Cornering

• Criteria
• Increase negative chamber change from -0.5o to
  -1.5o per inch of compression.

• Justification
• Increased tire angle increases lateral force in
  corner as long as contact patch is the same.

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Camber Thrust
For any given slip angle, negative camber
produces higher lateral thrust than zero camber
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Objectives
Improve Cornering

• Criteria
• Decrease center of gravity by 2 inches and
  increase track width by 2 inches

• Justification
• Reduces load transfer and increases cornering
  force

5
Objectives
Decrease Unsprung Weight

• Definition
• Weight of the suspension that is not supported by
  the spring. Approximately 50 of the control
  links are included in unsprung weight

• Criteria
• Decrease A-arm mass by at least 15

• Justification
• Increases responsiveness to improve road holding

6
Objectives
Decrease Cost

• Criteria
• Decrease overall cost by at least 15.

• Justification
• Improve cost report score
• Cost is 10 of the total vehicle score

7
Objectives
Meet SAE Rules

• Criteria
• Keep overall width under 64
• Grade five or better fasteners
• All fasteners must be captive (nylon lock nuts,
  cottered nut, or safety wired bolts

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Prototype Characteristics
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Prototype Characteristics

• Camber Change
• Increased negative chamber change from -0.5o to
  -1.56o per inch of compression.

• Mass
• Decreased A-arm mass by 39

• Dimensions
• Ride height was set at 10
• Overall vehicle width was set at 62

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Prototype Characteristics

• Cost
• Total cost was decreased by 25

• Fasteners
• Grade five fasteners and nylon lock nuts were used

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Cost Analysis

• Cost Discrepancy Justification
• SAE cost was determined by a cost per unit mass
  method
• Purchase cost was based on a cost per unit length
• Not all of the purchased materials were used to
  build the prototype

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Cost Analysis
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Cost Analysis
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Strain Gage Attachment

• UPPER ARM
• Gage 1 Stress in weld
• Gage 2 Axial stress in tube

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Strain Gage Attachment
LOWER ARM Gage 3,4,5 (Rosette) Combined stress
in lower tube Gage 6 Stress near weld
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Strain Gage Attachment
Gage 7,8,9 (Rosette) - check for bending Gage
10 - check for strain caused by the shock
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TEST RESULTS
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Upper A-Arm FEA

• Von Mises Stresses compared
• Maximum stress observed in the ball joint where
  tubes are welded
• Sharp change in geometry
• Stress riser

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Lower A-Arm

• Maximum stress seen in shock mounting tabs
• Stress appears higher than expected
• Testing did not show a failure

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Final Results

• Initially Used ANSYS
• Ran into Program Limitations
• Rotational Constraints
• Element number
• Used Mechanica for final analysis
• Lower A-Arm analysis indicates failure. However,
  physical testing does not support this result.

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Manufacturing

• Tubes
• Prototype
• Manually cut to length
• Notched on mill using hole saw
• Production
• Notching punch and die
• Press or hydraulic operation

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Manufacturing

• Lower ball joint mount
• Prototype
• Cylinder turned on lathe
• Angle cut on mill
• Production
• Cast

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Manufacturing

• Shock mount tabs and plate
• Prototype
• Drilled and cut
• Slot cut on mill
• Production
• Stamped

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Manufacturing

• Assembly
• Prototype
• Upper and lower jig built
• Manually TIG welded
• Production
• Automated TIG welding

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Possible Improvements

• Further tubing optimization
• Cross members may be unnecessarily large
• Review lower shock mount design
• FEA was inconclusive
• Further review may be needed to verify the safety
  factor

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Design Summary

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Questions