1. Mini Baja Suspension Design
ET 493 Senior Design – Spring 2017
Group: Advisor:
Tanner Harmon Dr. Ho-Hoon Lee
Ramon Viada
Instructor:
Dr. Cris Koutsougeras

2. Introduction
Our objective is to design and develop a suspension system for a mini baja car like the one pictured.
Using knowledge gained from courses in the Engineering Technology curriculum we can accomplish this task.

3. Background of Mini Baja (SAE Baja)
The Mini Baja is an event where engineer students from different universities across world come together to compete by putting Baja cars to the test.
The event is sanctioned by SAE, or the Society of Automotive Engineering.
The object of the competition is to simulate real-world engineering design projects and their related challenges. Each team is competing to have its design accepted for manufacture by a fictitious firm. 

4. Basics of Suspension
Suspension is a system responsible for dampening the forces acting upon the vehicle.
By using dampeners the ride quality can be altered in many different ways.
Dampeners vary: coil overs, coil spring and shock, strut and coil, air springs, etc.
The natural frequency of your vehicle is 1hz, which means the suspension cycles 1 full time each second.
What controls this frequency is the dampeners equipped in the system.
Having a frequency above 1hz correlates to a bouncy ride, frequency below 1hz correlates to a stiff ride quality.
The front suspension is equipped with upper and lower control arms to allow vertical articulation of the wheels throughout the suspension travel.
Rear suspension varies from solid axle systems to independent rear suspension which is setup very similar to the front suspension.
MSOE (Milwaukee School of Engineering) Design of spring system

5. Baja SAE Design Spec Sheet
2017
Competitors please replace the sample specification values in the table below with those appropriate for your vehicle and submit this as described in the rules. This information will be reviewed by the design judges and will be referred to during the design event.
--Please do not modify the format of this sheet. Common formatting will help keep the judges happy!
--The sample values are fictional and should not be used as the baseline for your designs. Please DO NOT make up values!
Car No.
SAMPLE (15)
School
University of Baja SAE
Dimensions
Front
Rear
Overall Length, Width, Height
95" (2413 mm) long, 62" (1575 mm) wide, 65"(1651 mm) high
Wheelbase
70" (1778 mm)
Track Width
55" (1397 mm)
50" (1270 mm)
Curb Weight (full of fluids)
436 lbs (198 kg)
Weight Bias with 150 lb driver seated
53%
47%
Weight with 150 lb driver seated
312 lbs (142 kg)
274 lbs (125 kg)
Suspension Parameters
Suspension Type
Dual unequal length A-Arm, Fox Podium X Coil over shocks, Adj. Roll bar.
Dual unequal length A-Arm, Fox Podium X Coil over shocks
Tire Size and Type
23x8-10 ITP Mudlite
Wheels (width, construction)
6" wide, Forged Al, 4/2 offset
7" wide, Forged Al, 4/3 offset
Center of Gravity Design Height
25" (635 mm) above ground (confirmed with testing (tip method))
Vertical Wheel Travel (over the travel)
6" (152 mm) jounce/ 4" (102 mm) rebound
7" (178 mm) jounce/ 5"(127 mm) rebound
Recessional Wheel travel (over the travel)
2" (50.8mm)
0" (0mm)
Total track change (over the travel)
3.5" (88.9mm)
4" (101.6mm)

6. Wheel rate (chassis to wheel center)
25 lbs/in (4.8 N/mm)
43.2 lbs/in (7.6 N/mm)
Spring Rate
100 lbs/in (17.5 N/mm)
120 lbs/in (21 N/mm)
Motion ratio / type
0.5 / linear
0.6 average actual progressive rate
Roll rate (chassis to wheel center)
4.14 degrees per g
Sprung mass natural frequency
1.2 Hz
1.5 Hz
Type of Jounce Damping
High and low speed adjustable
Type of Rebound Damping
Low Speed adjustable
Fixed
Roll Camber (deg / deg)
2.62 deg / deg
2.62 deg /deg
Static Toe
-0.2 deg toe (toe out)
0.3 deg toe in
Toe change (over the travel)
1 deg
0 deg
Static camber and adjustment method
-1.5 deg, adj. via outboard rod end on A-arm
-0.5 deg, adj. via inboard rod ends
Camber Change (over the travel)
6 degrees
4 degrees
Static Caster Angle
9 degrees, adjustable
0 degrees, non-adjustable
Caster Change (over the travel)
0 degrees
Kinematic Trail
2" (50.8mm)
Static Kingpin Inclination Angle
10 degrees non-adjustable
No Kingpin
Static Kingpin Offset
Static Scrub Radius
-1" (-25.4mm)
Static Percent Ackermann
60%
None
Percent Anti dive / Anti Squat
40% Anti dive
30% Anti Squat
Static Roll Center Position
12" (305mm) above ground
13" (330mm) above ground
Number of steering wheel turns lock to lock 3
Outside Turn Radius
15' (4.57 m) to right
16'(4.88 m) to the left

7. Mini Baja Objective Frame Suspension Steering Powertrain
Design frame to allow components to be held
Suspension
Design suspension system to allow a maintained 1hz for the natural frequency and also to aid in handling.
Steering
Design, adjust, and fine tune a steering system
Powertrain
Design the method of moving the car from A to B with a certain specified criteria, such as towing and acceleration.
In the end we would like to have a final, put together Baja, so Southeastern can join the Baja race in Spring semesters to come.

8. Suspension Objective
Our objective for this project is to knowledge gained through the ET curriculum along with knowledge gained independently to design a suspension system which will be part of a bigger project (Mini Baja). The suspension system should use the parameters specified in the SAE
We plan to learn more about the parts and mechanisms dealing with suspension systems. This includes how they work, why they work, as well as the math behind why suspensions systems can do wat they do.

9. Y=F(x)
By understanding basic geometry and trigonometry, we evaluated the figure to the right to be able to solve for the change in length of y.
The figure had to separated into 2 separate triangles to be able to properly solve for the change in length of y(dampener).

11. Force Equation
The next equation we were to derive was to show the forces of the shock/dampener as a function of the weight of the buggy.
The figure to the right is a free body diagram of showing the forces acting on the lower control arm.
By taking moment at the hinge where the lower control arm mounts to the frame this was possible.

13. Buggy Parts cost from buggydepot.com
Cost Analysis
Buggy Parts cost from buggydepot.com
Part
Each Part Price (U.S Dollars)
Quantity Needed
Heim Joint
$11.99 16
Steering Tie-Rods
$14 2
Lower Control Arm
$75 4
Upper Control Arm
$45
Shocks/Struts(dampener)
Wheel Hub
$65
Wheel Bearings $5
Spindle Kit
$110
By researching the average costs for buggies of similar design we found the average costs from buggyparts.com

14. Deliverables Derive equation of y = f(x) (Tanner and Ramon)
Derive equation of py (Tanner)
Force Equation (Tanner and Ramon)
Summation of Fy (Tanner)
Cost Analysis (Ramon)
Derive Dynamic equation of system (next semester)
Find the optimal K value for spring (next semester)
Design and develop control arms and mounts for front and rear suspension (next semester)

15. Future progress / next semester
To further design and develop the mini baja suspension system we will study and apply the energy method of dynamics to evaluate the energy transfer of the system to achieve a natural frequency of 1hz.
With given weight and lengths we could then calculate the proper mounting position and angle of the dampener which will allow the vibration frequency of 1hz to be achieved.