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
Existing Suspensions

Volkswagen
Trailing arm - most
common
Swing-Arm – Original
Design
Camber Gain

Tilt of wheels
towards vehicle.
 Ideal setup keeps
wheels
perpendicular to
ground.
Bump Steer
Steering Tie Rod
Path
Wheel
Travel
Rack and Pinion

The tie rod path
follows a fixed
radius.
 Wheel travels on a
separate path
 The difference in
these two causes
the wheel to turn.
Roll Center
Suspension Geometry

Point at which
Roll Center and Center of Gravity Locations
Lateral Loads act
Front Wheels
upon the vehicle
 Angle dictates force
Center of Gravity
distribution
 Location change is
critical
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.
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
i = steering angle inside
o = steering angle outside
100 = outside wheel angle at 100% Ackermann
%Ack erman n
Percent Ackermann
Turn Radius (feet)
Inside Wheel Angle (degrees)
Outside Wheel Angle (degrees)
Ackermann Angle
12
37.1
30.9
6.2
 i
 i
50
14
31.5
26.8
4.7
 o
 1 00
16
27.4
23.6
3.8
 1 00
12
37.1
34.6
2.5
20
14
31.5
29.6
1.9
16
27.4
25.8
1.6
12
37.1
37.1
0
0
14
31.5
31.5
0
16
27.4
27.4
0
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.
 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.
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
1
A
B
C
D
Orig
2
A
B
C
D
3
A
B
C
D
4
A
B
C
D
Upper Control Arm
Y Location Z Location
10.5892
9.577
8.038
8.691
8.369
7.034
8.872
4.218
2.91
2.88
Lower Control Arm
Y Location Z Location
2.91
2.88
10.5892
8.038
8.369
8.872
9.577
8.691
7.034
4.218
4.04
1.0
10.5892
8.038
8.369
8.872
9.577
8.691
7.034
4.218
5.04
1.0
10.5892
8.038
8.369
8.872
9.577
8.691
7.034
4.218
8.04
1.0
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.
Steering Arm Length (inches )
20% Ackermann Steering Arm Length
18.00
16.00
14.00
12.00
10.00
20% Ackermann
8.00
6.00
4.00
2.00
0.00
0
10
20
30
Turning Radius (feet)
40
50
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
Toe-In vs. Displacement in Jounce
15.00
Toe-In (deg)
10.00
5.00
0.00
-7
-6
-5
-4
-3
-2
-1 0
-5.00
1
2
3
4
5
6
7
Original Design
Trailing Arm
New SLA Design
-10.00
-15.00
-20.00
Wheel Displacement (inches)
Toe-in vs. Roll Angle in Roll
Toe-in (deg/deg of roll)
10.00
8.00
6.00
Original Design
4.00
Trailing Arm
New SLA Design
2.00
-15.00
-10.00
0.00
-5.00
0.00
-2.00
5.00
-4.00
Roll Angle (deg)
10.00
15.00
SuspensionGen Comparisons
Camber Gain vs. Displacement in Jounce
Camber Gain (deg/in of
travel)
1.00
0.50
0.00
-10
-5
-0.50 0
5
10
Original Design
-1.00
Trailing Arm
-1.50
New SLA Design
-2.00
-2.50
-3.00
Displacement (in)
Camber Gain (deg/deg of
roll)
Camber Gain vs. Roll Angle in Roll
0.50
-20.00
0.00
-10.00 -0.500.00
-1.00
-1.50
-2.00
-2.50
-3.00
Roll Angle (deg)
10.00
20.00
Original Design
Trailing Arm
New SLA Design
SuspensionGen Comparisons
Roll Center Height vs. Roll Angle in Roll
Roll Center Height (in)
60.00
50.00
40.00
Original Design
30.00
Trailing Arm
20.00
New SLA Design
10.00
-15.00
-10.00
0.00
-5.00
0.00
-10.00
5.00
10.00
15.00
Roll Angle (deg)
Roll Center Lateral
Migration (in)
Roll Center Lateral Migration vs. Roll Angle in Roll
-20.00
10.00
8.00
6.00
4.00
2.00
0.00
-10.00 -2.000.00
-4.00
-6.00
-8.00
-10.00
Roll Angle (deg)
Original Design
10.00
20.00
New SLA Design
Results
Jounce
Suspension Model
Volkswagen
Original Design
New Design
Max
Min
Max
Min
Max
Min
Roll Center
Lateral
Camber
Tread
Height (in) Migration (in) Gain (deg/in) Change (in)
2.19
0.43
0.36
N/A
-2.74
-0.3
0
23.48
-2.26
4.74
N/A
6.61
-2.51
-8.7
13.74
0.46
2.58
N/A
3.74
-1.74
-4.88
% Change VW
% Change Original
120.35%
45.57%
Toe-In
Roll
(deg) Steer (deg)
10.47
1.64
-0.89
-5.17
11.34
-0.86
-16.03
-1.48
1.14
0.2
-0.87
-0.12
89.11%
87.80%
89.95% 123.26%
Roll
Suspension Model
Volkswagon
Original Design
New Design
% Change VW
% Change Original
Max
Min
Max
Min
Max
Min
Roll Center
Lateral
Camber
Tread
Height (in) Migration (in) Gain (deg/in) Change (in)
53.14
1564.08
0.06
0.34
-0.01
-1564.08
-0.02
0
16.23
7.32
-2.39
0
13.5
-7.32
-2.49
-1.98
9.28
2.06
-0.64
0
8.32
-2.06
-0.91
-1.15
255.34%
173.63%
72.17%
Toe-In
Roll
(deg) Steer (deg)
7.8
-0.01
-0.89
-1.82
-0.59
-1.05
-2.35
-1.15
0.3
0.08
-0.59
0.03
Large
95.60%
298.31%
Large
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?