On Sat, 14 Sep 2002 10:15:05 +0200, Stefan Larsson
...
>> If you hit the bump stop you're hitting another, much stiffer, ***
>> spring in series with the suspension spring. F=k*d then becomes F=k*d^2
>> ;-) Kidding again of course, but you've got another spring rate to add
>> in at that point.
>The bump spring rates are usually very high which put rather annoying
>demands on the numerics. I don't know how the simulation is performed,
>but if it is done solving e.g. a state-space using a fixed step
>ODE-solver like Runge-Kutta 4th-order, the system will probably get
>unstable...
I thought ODE was actually using a modified Euler-type integration,
although I'm not sure what the 'modified' entails. :)
I actually use implicit integrations for the movement of the wheels,
in a fixed timestep (500Hz, can be upped to 1000Hz which is nicer for
F1 cars). The thing is that I have wheels that have mass (it seems
easier for some to see the wheels as having no mass), and for the road
force I use the tire rate (F_road_vertical=tireRate*d where d is the
distance the tire is 'in' the track).
Tire_rates are probably even worse than bump stop rates (hm, or
perhaps just in the same regime). About 10x as high as suspension
rates. Given a F1 or Cart car, normal Euler integration was not really
handy.
With implicit integration this seems to work much more ok (time
reversal).
So in fact I may be able to just include the bump stop rate and do a
combined bumpStopRate and springRate. But as you bump quite
unpredictable anyway, just using the tire rate directly and
hard-locking the wheel position at its outer limit may be good enough.
Once the car really sinks in even then the car chassis bounding box
should deal with the collision. Until I want to surpass Stuntman. ;-)
(nice game, although it's a shame it seems to have digital controls
and some kind of track caching would have been almost vital).
I have an idea also that some cars are given too little space for its
springs to move in (only 5 cm's up & down for example) which can
trigger the problem.
Ruud van Gaal
Free car sim: http://www.racesimcentral.net/
Pencil art : http://www.racesimcentral.net/