SunRayce Front SunRayce Front Suspension AnalysisSuspension Analysis

Jonathan Walker

Lars Moravy

Ian Harrison

Alexander Ellis

ME 224

December 12, 2001

IntroductionIntroduction 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 2001. 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

PurposePurpose

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.

BackgroundBackground

Ftangent—A-arms

Fnormal—Push-rod

Ftangent, max = * Fnormal

Experimental SetupExperimental 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 SetupExperimental Setup

POTENTIOMETER:– Mounted on Pivot Point of

Suspension– 5 K Range– Wired to DAQ and Laptop– Inputs to LabVIEW

Program

TheoryTheory

STRAIN GAUGES:– Wheatstone Bridge vo/(vs*Sg)– Op-Amp

(100 X Signal Amplification)

POTENTIOMETER:– Variable resistance circuit– Angular-linear displacement ratio:

1 inch = 224.6 Ohms

R2 = (R1 * V2) / (V - V2)

TestingTesting

AcceleratingCorneringBumps

Results and DataResults and Data

Smooth Road– Strain Range

-0.083 to –0.076

– Steady State m = -0.08

Smooth Road

-0.084

-0.082

-0.08

-0.078

-0.076

-0.074

Time (sec)

Str

ain

(u

m/m

)Smooth Road

-0.15

-0.1

-0.05

0

0.05

0.1

Time (sec)

Dis

tan

ce (

in)

Results and DataResults and Data

Over a PipeStrain SpikeDisplacement

– Back Tire SpikeBar impact

Bar impact

Running Over Pole

-0.14

-0.12

-0.1

-0.08

-0.06

-0.04

-0.02

0

Time (sec)

Str

ain

(u

m/m

)

c

Running Over Pole

-0.8

-0.6

-0.4

-0.2

0

0.2

0.4

0.6

Time (sec)

Dis

tan

ce (

in)

Design Limit Calculations Design Limit Calculations

FATIGUE ANALYSIS: Endurance limit

– Se’ = 0.45 Su

– Se’ = 363 Mpa

FATIGUE ANALYSIS:Modified endurance limit:

Se = kf * ks * kr * kt * km * Se’

kf = ks = kt = km =1

kr = 0.9 {for 90% survivability}

Se = 0.9 Se’ = 327 MPa

[Se = 327 Mpa] > [max = 1.01E7]

Infinite life without fatigue failure !!

Design Limit Calculations Design Limit Calculations

FATIGUE SAFETY FACTOR:

a = max. expected amplitude of stress on the push-rod

m = mean expected stress on the push-rod

kf * a / Se + m / Sut = 1 / ns

7.83-3 + 9.29-3 = 1 / ns

0.0171 = 1 / ns

ns = 58 <= too high!

Design Limit Calculations Design Limit Calculations

IMPACT LOADING:

 Impact Factor, Im = Pmax / Pavg = 1.69 E3 N / 5.07 E2 N = 3.333

Impact stress, i = Pmax / Area = 1.69 E3 N / 1.576 E-4 m2 = 1.07 E8 Pa

  

IMPACT LOAD SAFETY FACTOR:

 

Yield Stress, Sy = 8.07 E8 Pa

 

ns = Sy / i = 8.07 E8 Pa / 1.07 E8 Pa ~ 8

Design Limit CalculationsDesign Limit Calculations

YIELD ANALYSIS:

max = 1.017 Pa

y = 6006 = 68 Pa {for 4140 steel}

[y = 68 Pa] > [max = 1.017 Pa]

     will not yield

YIELD SAFTEY FACTOR:

ns = 68 / 1.017 = 60

too high !!!!!

ConclusionsConclusions

Present situation– Too robust, too heavy

Redesign options– Change materials:

aluminum alloy (whole frame?)

Further Testing Needed and Allowable– Varying Car Speed, Turning Radii