FSAE Suspension
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Transcript of FSAE Suspension
7/16/2019 FSAE Suspension
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Final Presentation to Engineering Panel
Seth Beckley, Kevin Gygrynuk, Josh Hilferty, Mike Teri
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FSAE “The Formula SAE ® Series competitions challenge
teams of university undergraduate and graduatestudents to conceive, design, fabricate and compete
with small, formula style, autocross racing cars……Over the course of three days, the cars are judged in aseries of static and dynamic events including:technical inspection, cost, presentation, andengineering design, solo performance trials, and highperformance track endurance.”1
1 http://students.sae.org/competitions/formulaseries/west/eventguide.pdf
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Sponsor Mike Hawley
Employed by W. L. Gore
Former UD FSAE member, designed the suspensionsystem for two consecutive years
Resource of much valuable information on suspension
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Suspension: How it Works Key Parts:
upright
lower a-arm
upper a-arm
Spindle/
rotor red = points fixed
to chassis
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Key Parts Continued
pushrod
rocker
(bell crank)shock
red = points fixed
to chassis
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Key Parts: Sway Bars and Tie Rod
Sway Bar
sway bar arm
and linkage to
rocker
tie rod to
Steering rack
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Suspension: How it WorksKey Terms:
Camber: The angle of the wheel with respect to vertical.
Kingpin Angle: The angle measured between the steering axis and vertical.
Scrub Radius: The distance between the steering axis and the wheel’s contact patch.
Image taken from: www.mgf.ultimatemg.com/
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Suspension: How it works Roll Center:
Defined by intersection of lines between the tire contactpatch and instant centers of wheel travel.
Defines the instantaneous point about which thechassis rolls
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Key Terms: Anti-Dive: A suspension geometry setup that resists the diving action of the nose of the
car from diving during braking Anti-Squat: A suspension geometry setup that resists the diving action of the tail of the
car from diving during acceleration
Center of Gravity
A-arms
The closer the convergence points are to the height of the center of gravity, the more anti-
dive or anti-squat characteristic is present
Image taken from Competition Car Suspension, Allan Staniforth
Suspension: How it Works
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Project Scope Determination of most efficient suspension configuration and
geometry Determination of spring and damper requirements Determination of anti-dive/anti-squat requirements
Determination of optimal values for camber, caster, and kingpin anglesas well as scrub radius
Determination of attachment points at wheel, brake, steering rack,axle, and chassis interfaces
Design based off of existing wheels and tires Design synthesis and real-time simulation of complete and functional
suspension system Output a working, useable suspension system for the 2010-2011 UD
FSAE car Maintain a high level of easy adjustability for further tuning of the
suspension system
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FSAE Rules Applicable to
Suspension Minimum wheelbase of 60”
If front and rear track are of different lengths, smaller
track must be at least 75% of larger track
Minimum of 2” useable wheel travel
Minimum of 1” jounce
Minimum of 1” rebound
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Additional Constraints Budget of $1000
Constraints imposed by other teams Drivetrain – axles and rear hubs
Driver controls - steering rack location
Chassis – construction of chassis
Cooperative – brake rotor and caliper selection
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Metrics and Target Values Wheelbase: 61” Front Track: 50” Rear Track: 2” less than front Adjustable Anti-Dive and Anti-Dive: 1” vertically on specific pickup points
Roll Center: Stable, < 1” vertical movement over 1.5” deflection in roll, < 1’horizontal movement Scrub Radius: < 1” Camber: -2⁰ static camber, maintained over ¾” deflection in roll Kingpin Angle: 0-5⁰ Caster Angle: 0-5⁰
# Tools to Adjust and Tune Suspension: 3 tools Adjustments easy to access: Yes Camber and toe adjustment without disconnection of parts: Yes Material Strength: Factor of safety for range of normal operation: > 2 Material Machinability: Maximize Material Weight: Minimize
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Suspension Style Choice Unequal A-arms
Most commonly used for racing suspension, almostexclusively used in FSAE
Style most suited for stiff racing independentsuspension
Reliable, with predictable and calculable motions andforces throughout travel.
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A-arm Length Adjustability Threaded Chassis Mount
Typical and reliable method, maximize strength and rigidity
Threaded A-arm
mounts to chassisspherical rod end
To adjust, bolt is removed,
Locknut loosened, and
rod end turned
Locknut
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Camber Adjustability Shims at upright Particular shim thicknesses
can be correlated tospecific camber changes
Easily adjustable: loosen bolts
and drop shim into place
Reliable and successful concept,
upright a-arm clevis
shim
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Anti-Squat and Anti-Dive Adjustability
Anti-Squat and Anti-Dive Adjustability
Adjustment is achieved by switching out different sets of bushings.
Bushings are cheap and easy to manufacture.
bushing
bushing
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Kinematic Design Extensive use was made of
Excel spreadsheets anddynamic CAD models tosimulate suspension andachieve desired performance
characteristics. Two Dimensional Simulation
of Suspension in Roll
-20
-15
-10
-5
0
5
10
15
20
25
30
-30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30
Y
( i n
)
X (in)
Body Roll Simulation
Neutral
1.5" Deflection Right Roll
1.5" Deflection Left Roll
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Lower A-arms Dimensions determined by kinematic and force
analyses.
Design based on vehicle dynamicstheory and researchof previously successful designs.
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Upper A-arms Dimensions determined by kinematic and force
analyses.
Design based on vehicle dynamicstheory and researchof previously successful designs.
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Push Rod Design Transfers bump force to shocks
Supports weight of car in neutral stance
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Rocker Design Determines ratio of pushrod motion to spring
compression.
Linkage point for sway bar
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Sway Bar Design Individual project
assigned toSeth Beckley
Typical FSAE designstyle
Stiffness adjustability
achieved by changinglever arm length
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Force Analysis The force analysis on the final design centered around
maximum cornering and braking forces estimatedduring competition.
The team decided upon a goal of structural integrity through a 5g vertical impact.
The estimated braking and turning values were
conservative, and surpassed the benchmarked 1.4 gexpected in competition.
The rockers were designed to optimize the travel of theshock absorbers.
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Force Analysis Factor of Safety
The factor of safety for the suspension components undernormal turning and breaking is over 5.
Failure of Components The rod ends are the weakest members of the suspension
structure, and have an estimated failure rating of 4500 lbf . Rod ends are expensive and not as easy to replace as other
hardware so the mounting bolts have been undersized toprovide a factor of safety less than the components
themselves. Finite Element Analysis
A finite element analysis was conducted using solid modelingtools as well as manual calculations to ensure eachcomponent’s performance
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Ride and Roll Rates Using vehicle dynamics theory, shock travel limits, and
bump and cornering conditions, desired ride and roll rates were determined:
Ride Rate:
Front: 148.4 lb/in
Rear: 146 lb/in
Roll Rate: Front: 18750 lb•ft/rad total, 15483 lb•ft/rad contributed by
springs, 3267 lb•ft/rad contributed by sway bars
Rear: 20875 lb•ft/rad total, 14016 lb•ft/rad contributed by springs, 6859 lb•ft/rad contributed by sway bars
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Spring Stiffness and Damping Spring Stiffness was determined by desired ride and
roll rate, and the ratio between pushrod movementand spring compression.
Damping can be guessed at, but not dialed in until caris driven and tested.
From spring stiffness calculations, the target
suspension frequency was estimated to be 3 – 3.5 Hz which can be achieved through shock adjustability.
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Final Product To determine the achievement of the geometric target
values the suspension was assembled onto the partially completed frame and measured.
Assembly will continue throughout the final week of Phase 4.
The final assembly of the suspension will then be
presented to the sponsor on December 17th
2010.
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Performance Evaluation/Validation Chromoly tubing and welded connections will be tested to
failure and compared to force analysis during the final week of the Fall 2010 semester.
The car will not be completed until the very end of seniordesign, and thus testing of the effectiveness of the system
will have to be postponed until winter session.
A test plan has been developed to analyze the performance
under driving conditions. Once the car is built, the UD FSAE club will take over
testing and tuning of the suspension using methodsoutlined by Team Suspension
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Performance Evaluation Measures Camber Effectiveness: Tire temperature analysis
after test runs
Load Transfer: G force measurements from onboarddata acquisition
Jounce, Body Roll & Anti Squat/Anti-Dive: onboardmeasurement and tuning
All evaluated performance measurements can beadjusted through adjustability in the suspension and will be tuned to optimal properties.
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Camber Effectiveness The efficiency of the camber, ride, and roll rates can be
measured by analyzing tire temperature distributionafter 5-10 laps around the track.
Each tire’s temperature will be measured at threelocations on the tire 1” from the outside shoulder
1” from the inside shoulder
Center of the tire Possible results of the tests and their solutions have
been outlined in the test plans given to the UD FSAEclub.
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Load Transfer G-force analysis will be completed through the car’s
onboard computer.
Acceleration measurements will be recorded at every point along the line the car travels around the track.
The data extracted from the computer will enable theteam to calculate resultant G-forces.
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Jounce, Body Roll & Anti Squat/Anti-Dive
These performance targets will be evaluated by directly measuring them as the car is put throughtesting on the track.
Under maximum braking, accelerating, and corneringconditions, these properties will be measured.
From this analysis the car will be finely tuned to
achieve the set target values.
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Budget Materials Cost = $322
Aluminum, Steel, Chromoly Tubing
Parts Cost = $550 Bearings, Rod Ends, Spherical Joints, hardware
Miscellaneous Costs = $100
Manufacturing Cost = ~$0.00
All fabricating was done by team in FSAE shop andstudent shop at no charge
Total Cost = $972
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Project Management The design of each component in the suspension
assembly have been completed and optimized.
All geometrical target values have been met.
The suspension will be tuned after testing iscompleted in order to satisfy performance metrics.
Budget has been reduced and falls within the
constraint. Team is on schedule to finish project and present
results to the sponsor on December 17th 2010.
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Questions?