A summary of points relevant to our car
Onboarding Resource
Static Analysis -Front Suspension
inside wheel of solar car vs FSAE usually outside wheel analysis because N force >
Force analysis and designing parts for loads
2g bump, 1g lateral force turn, 1g braking input forces referenced to the contact patch
keep in mind the changes in N force during all ^ behaviors
MINIMUM
statics problem w 3 torques 3 forces
if pass forces on one component - pass to the next component - to the frame - determine if the frame mounting point will fail at these conditions
combined loading conditions AND separated loading conditions
one loading condition may be HELPING the other one - so important to do combine + separate because it may pass in combined but not separate
ex) braking + cornering - cornering may be helping alleviate the > N force on front axles during braking and < load from pitching forward - vice versa
brake perform analysis
VDR Requirements - will car survive brake system, will brake system survive, will car perform and pass dynamics brake performance (4.7 m/s^2)
pedal force required? - panic stop - when our car is decelerating at this rate ^ (to pass) then how much is the pounds of force on pedal to achieve that?
is this a reasonable number? too much or too little force to achieve is not good
hard to modulate brakes that react too easily - preventing from locking up
convergent behavior
what point do front lock up vs required force to gen 4.72 m/s^2 gradual braking
50 lbs F to braking performance vs 60 lbs to lock up - driver needs to be good at working in the spot between - decelerating but not locking up
at point F wheels lock up - did rear wheels lock up yet
wheels that lock up are not preventing slip - no lateral acceleration or cornering force
locked up wheels have now lost their ability to stop themselves from sliding
front with braking force and imbalances / if one wheel is more brake force or CG not centered or sidewind - back wheels will slide to one side and create a yaw and now unstable = spinout
sim - 200lbs F on the brake pedal and box - does the mount and hydraulics survive?
sample brake calculations
Camber gain from bump - good because roll out and camber neg counteracts roll (counteracting the wheel from lean out or pos camber induced by roll) and in theory the wheel will be up and down and leaning out less
shorter upper A arm and longer bottom for negative camber gain
angled up upper A arm / tilt it down to inboard
change the lengths of control arms, angle of them → optimizing for camber gain
Scrub caused by bump - reduce > bc > energy loss
caused by suspension motion → lateral component - lateral movement of tire side to side
bump - suspension compresses - angled arms become horizontal and push the wheel out - vice versa, creating a scrub radius from bump
aim to keep contact patch at same point - the tire can move ( camber change?) - optimizing for negative camber gain in bump doesnt solve this though
neutral bump start with control arms horizontal - the displacement when the control arms change angles during dump will be less
longer control arms CAN decrease scrub but also decrease camber gain - compromise
Leading arm suspension - MIN scrub bc constrain to vertical movements but V LITTLE camber gain
control arms and inboard and outboard same
Nat frequency to determine springs - easy method for solar cars - take calc weight from axle and derive springs from that natural frequency - consider when motion ratios are factored in
front > natural frequency than rear - can do rear x 1.15 = front
effective spring rate at the wheel finding
> frequency = > stiffness = < grip - soft suspension / soft and high temp tires > grip
→ front understeer bc of the grip - obviously more grip means more potential to oversteer
passenger cats 1.0 - 1.3, sports sedans 1.2 - 1.5, sport cars 1.5 - 1.8
more damper dependent ^ when softer
race cars w aero > 1.8 frequency - > stiffness so vehicle handling < performance