Over the past month, I've been tinkering with a spreadsheet and made something useful of it.
It starts at the statics page with whole-vehicle parameters. Some of the design aspects can be worked both ways: eg. the ride frequency is used to calculate spring rate, or spring rate is used to calculate frequency. This sheet was originally written by someone at Queensland Univ, but I have been unable to contact them for permission. I may have to rewrite this part.
Calculates these parameters:
-damped, undamped and equivalent natural frequency
-spring rate
-wheel rate
-damping ratio
-damper rate
-body roll and corner weights for a given lateral accel
-pitch and corner/axle weights for a given accel/braking
-static spring position, given the free length
-roll resistance ratio
It solves the 3D kinematics for a dual-wishbone suspension with either a direct acting or bellcrank driven spring/damper. The pushrod can be mounted on the upright or either arm. The design flow is something like this:
1) take upright dimensions and apply camber/caster/toe and move laterally to contact patch point and vertically by tire rolling radius.
2) this defines the position for the upper and lower joint
3) find virtual point on chassis to make hinge joint for upper and lower arms-> calculate link lengths
4) use the damper chassis mount point, the pushrod mount point, and a '3rd point' to make a planar rocker mechanism, given the rocker arm lengths, rocker angle, and the entry angles of the damper and pushrod.
Calculates these parameters:
-instantaneous center
-roll center
-kingpin ground intercept
-scrub radius
-mechanical trail
There is an Actuation sheet where you can change the chassis heave, roll, or steering and see the result in a front view XY chart of all the link positions. It also calculates these parameters (and delta from static):
-camber
-caster
-single wheel toe
-total toe
-wheel track
-damper length
-driveshaft length
-CV inner angle
-CV outer angle
-%ackerman
-roll center height/lateral
The plots sheet runs a macro that iteratively calculates heave, roll, and steer curves for common values.
vs heave:
toe, camber, damper(gives motion ratio), roll center height
vs roll:
toe, camber, damper, roll center lateral movement
vs steer:
toe, camber, caster
A braking sheet compares your front/rear brake balance from both the design side and the dynamics side. I started working on some energy/heat calculations as well.
I'm working on a website right now, but the spreadsheet will sell for US$45. The sheet is not locked or password protected in anyway, as you FSAE'ers are a smart bunch and would crack it anyways. The idea is that if enough people buy it then I'll keep working on it and make it better.
I've already tried to post this three times, so I'll stop here then edit as I go. Something in my message triggers the moderation filters and it seems to be posting links. You would think being a forum member for 7 years would count for something! Send me a PM or email and I'll send the links to the screen shots. Perhaps someone could post them for me.
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