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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