SunRayce Front Suspension Analysis Jonathan Walker Lars Moravy Ian Harrison Alexander Ellis ME 224 December 12, 2001

Introduction SunRayce is a nation wide competition that allows college teams to design, build and race solar cars. The Northwestern Solar Car Team built a car that competed during the summer of Currently the team is preparing to build the second-generation car, improving on previous efforts. After benchmarking other teams, Northwestern determined that the key strategy to producing a more successful car is to significantly reduce the car’s weight. The team asked our group to assist them by collecting data on the forces on the suspension. With this information, a future design can be optimized for lighter weight. Ian

Purpose The purpose of this experiment is to determine the magnitude and frequency of the forces acting on the front suspension of the solar car. To carry out the experiment, we utilized every tool learned in ME 224, from signal conditioning to LabVIEW programming. Our experiment will provide information necessary to improve the SunRayce vehicle, hopefully contributing to a strong Northwestern finish at next year's competition.

Background F tangent —A-arms F normal —Push-rod F tangent, max =  * F normal

Experimental Setup STRAIN GAUGES: – Mounted on Axial Strut Push Rod – Axial and Transverse Orientation – Wheatstone Bridge Setup – Wired to DAQ and Laptop – Input to LabVIEW Program

Experimental Setup POTENTIOMETER: – Mounted on Pivot Point of Suspension – 5 K  Range – Wired to DAQ and Laptop – Inputs to LabVIEW Program

Theory STRAIN GAUGES: – Wheatstone Bridge –  v o /(v s* S g ) – Op-Amp (100 X Signal Amplification) POTENTIOMETER: – Variable resistance circuit – Angular-linear displacement ratio: 1 inch = Ohms R 2 = (R 1 * V 2 ) / (V - V 2 )

Testing Accelerating Cornering Bumps

Results and Data Smooth Road – Strain Range to –0.076 – Steady State  m = -0.08

Results and Data Over a Pipe Strain Spike Displacement – Back Tire Spike Bar impact

Design Limit Calculations FATIGUE ANALYSIS: Endurance limit –S e ’ = 0.45 S u –S e ’ = 363 Mpa FATIGUE ANALYSIS: Modified endurance limit: S e = k f * k s * k r * k t * k m * S e ’ k f = k s = k t = k m =1 k r = 0.9 {for 90% survivability} S e = 0.9 S e ’ = 327 MPa [S e = 327 Mpa] > [  max = 1.01E7] Infinite life without fatigue failure !!

Design Limit Calculations FATIGUE SAFETY FACTOR:  a = max. expected amplitude of stress on the push-rod  m = mean expected stress on the push-rod k f *  a / S e +  m / S ut = 1 / n s 7.83   -3 = 1 / n s = 1 / n s n s = 58 <= too high!

Design Limit Calculations IMPACT LOADING: Impact Factor, I m = P max / P avg = 1.69 E3 N / 5.07 E2 N = Impact stress,  i = P max / Area = 1.69 E3 N / E-4 m 2 = 1.07 E8 Pa IMPACT LOAD SAFETY FACTOR: Yield Stress, Sy = 8.07 E8 Pa n s = Sy /  i = 8.07 E8 Pa / 1.07 E8 Pa ~ 8

Design Limit Calculations YIELD ANALYSIS:  max = 1.01  7 Pa  y = 600  6 = 6  8 Pa {for 4140 steel} [  y = 6  8 Pa] > [  max = 1.01  7 Pa]  will not yield YIELD SAFTEY FACTOR: n s = 6  8 / 1.01  7 = 60 too high !!!!!

Conclusions Present situation – Too robust, too heavy Redesign options – Change materials: aluminum alloy (whole frame?) Further Testing Needed and Allowable – Varying Car Speed, Turning Radii