Mini Baja Suspension Design ET 494 Senior Design – Fall 2017 Group: Advisor: Tanner Harmon Dr. Ho-Hoon Lee Ramon Viada Instructor: Dr. Cris Koutsougeras

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.

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. 

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

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)

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 0.4-0.7 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

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.

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.

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).

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.

Vibration Frequency Equation 𝑚 𝑥 +𝑘𝑥+𝑐 𝑥 𝒚= 𝑳 𝟐 𝟐 + 𝑳 𝟏 𝟐 + 𝑳 𝟑 𝟐 +𝟐 𝑳 𝟐 𝒙−𝟐 𝑳 𝟏 𝑳 𝟑 𝟐 − 𝒙 𝟐 𝑦 = 𝑙 2 𝑦 + 𝑥 𝑙 1 𝑦∗ (𝑙 3 2 )− 𝑥 2 𝑦 = (𝑙 3 2 )∗ 𝑙 1 𝑦( 𝑙 3 2 − 𝑥 2 ) 3/2

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

Cost Analysis Continued Construction Materials Material/Component Cost Quantity Hr(Labor in Constructing) 1” dom tubing .065 wall (cold rolled steel A513) Varies from $10 a foot online to $20 a foot 16 ft (with some margin for errors) 80 Hrs (designing and calculating) 80 Hrs(fabrication) Heim Joints $11.99 16   Ball Joints $12-$15 4 Ball Joint Mounts ? Tie Rod Ends $14 2 Shocks/Dampeners $45-100

Deliverables Linearize equation (completed) Derive equation of y = f(x) (completed) Derive equation of py (completed) Derive Dynamic equation of system (completed) Find the optimal K value for spring (late September - early October) Design and construct control arms and mounts for front suspension (late October) Design and construct control arms and mounts for independent rear suspension (late October) Assemble final buggy with all components. (November)