Dune Buggy Suspension and Steering Design Nate Dobbs Steve Myers Faculty Mentor: Dr. Richard Hathaway Industrial Mentor: David Myers

Overview Problem Goals of Project Terminology Analysis Optimization Final Design

Current Design Instability

Current Suspension Shortfalls

Goals of Project Re-design current front suspension and steering. Maximize performance in a sand environment by optimizing: Camber Gain Bump Steer Roll Center Height Ackermann Steering Toe-In Need Short-long Arm suspension, and steering that would minimize bump-steer. Camber Gain – dictate camber gain to keep wheel perpendicular to the ground. Minimize Bump Steer

Existing Suspensions Volkswagen Trailing arm - most common Swing-Arm – Original Design Swing-Arm Configuration Uses Ford Escort Rack and Pinion Custom Made components

Camber Gain Tilt of wheels towards vehicle. Ideal setup keeps wheels perpendicular to ground.

Bump Steer The tie rod path follows a fixed radius. Wheel travels on a separate path The difference in these two causes the wheel to turn. Steering Tie Rod Path Wheel Travel Rack and Pinion

Roll Center Point at which Lateral Loads act upon the vehicle Suspension Geometry Point at which Lateral Loads act upon the vehicle Angle dictates force distribution Location change is critical Roll Center and Center of Gravity Locations Front Wheels Center of Gravity Theta – Angle b/t the yellow line and the ground, determines the amount of lateral cornering forces that go either into vertical displacement of the suspension, or to rolling the vehicle about the CG. Distance b/t the Roll Center and the CG is the lever arm for a roll moment Roll Center

Effects of Roll Center Height on Suspension Roll Center to C.G. distance is related to force seen by springs/dampers The distance from the ground to the roll center is force seen by the geometry. Theta Dictates Proportion Change of Lateral Force reaction to Vertical Force Reaction Dist. B/T the RC and CG is amt of force vector seen by the springs/Dampers Dist b/t the RC and ground is force seen by geometry 40% 60%

Ackermann Steering Steering angles to travel perfect concentric circles Shown in the form of a percentage. Ackermann angle is between the two wheels 0% is with parallel front wheels

Ackermann Steering Mention why chose 20% Ackermann, THE CHOICE in turning radius, which will be discussed later, will also determine the Steering Arm length)

Rack & Pinion Selection The rack and pinion changes rotational motion of the steering wheel into linear motion. Ford Escort Rack and Pinion was 2.45:1 ratio. 1 revolution of the wheel resulted in 2.45 inches of linear travel.

Rack & Pinion Selection A smaller ratio means more movement to make a tight turn. A 5:1 ratio rack and pinion was incorporated into the design Full Range of Wheel motion in less than one full turn of the wheel.

Benchmark (Trailing Arm) Excellent for minimal camber gain. Inexpensive and widely available. Poor Bump Steer characteristics. Poor Adjustability.

Original Design Swing Arm configuration. Center of Gravity at 20.74 inches from the ground. Roll Center Height at 16.5 inches from the ground. Swing Arm configuration. Custom – more expensive, not adjustable Unacceptable Bump-Steer

SuspensionGen Analysis Trailing Arm configuration from benchmark data. Could not analyze 12 inches of travel. Poor results in all areas. Travel limitations - due to suspension limitations Camber gain was zero, but this means that in a Roll, the tire is at an angle to the ground.

SuspensionGen Analysis Original Swing-Arm Model Poor results at extremes of suspension travel Large Camber Gain, bump-steer

Final Design Optimization

Final Design Optimization 17 configurations were evaluated Varied A-arm location points within geometry. Selection 3D gave the best results. Optimized Camber Gain Good Roll Center Height Poor Toe-in and Bump Steer

Steering Arms Steering arm length graphed with turning radius. Based on 20% Ackermann configuration. 12 foot turning radius was desired. This resulted in a 5 inch steering arm.

Bump Steer/Toe-in Analysis Bump steer and toe-in vary with rack positioning. Angle between tie rod and wheel axis gives Ackermann Steering The steering arm and suspension move about similar radius, minimizing bump steer.

SuspensionGen Analysis Final Design Analysis performed with 12 inches of travel. Good results in roll and vertical displacement.

New Design

New Design

Finite Element Analysis AISI 1020 Steel was used due to availability and cost. FEA analysis was used to determine material size Shows results of these forces in displacements and stresses. A 0.189 inch wall thickness tubing was used and allowed for a significant factor of safety.

SuspensionGen Comparisons

SuspensionGen Comparisons

SuspensionGen Comparisons

Results

Review Sand Dune Buggy Stability Evaluated 3 designs Developed Short-Long Arm Solution Optimized Geometry, Steering, and handling characteristics All original goals were met.

Questions?