rec.autos.simulators

  I guess what I was really trying to say here was that according to friction
circle theory (from what I thought I got out of it, anyway), if the tire's
maximum force is being applied along the tire's longitudinal axis, there is
none left for lateral force.  Matt indicated that he liked to include some
lateral force anyway, because otherwise there can be very strong yawing
tendencies.  With 0 lateral force at the rears, you can spin around rather
quickly.  For instance, if the tire's spinning wildly, at 100 slip ratio, all
the available force should be applied along the longitudinal axis according to
what little I've read on friction circle use.  I agreed with his approach,
saying it would probably be best for me to go ahead and allow a small amount of
lateral force anyway.  

  That's already included in my model when calculating the instantaneous
direction of each tire, before finding the tire heading, and before subtracting
the two to find the slip angle.

  By "a component", you mean the lateral component.  I think I see what you're
doing.  You're letting the velocity vector define the total available force
(and possibly limiting it if it gets too big), then braking it into lateral and
longitudinal components if you want to analyze those seperately.  This way,
even a wildly spinning tire that has some slip angle/lateral movement will
produce a lateral force.  That's interesting.  Different from what I'm doing.
I'll ponder that awhile :0)

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://www.racesimcentral.net/

  Thanks,

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com

"J. Todd Wasson" a crit :

Well, the main problem was that at high slip angles there is a static lateral
forces ...

if we look the factor = f( slip_angle),  if slip_angle > 15 factor = 0.75 and
Lateral force = tire_load * factor.

So at low speed ,in theory there is an oscilation because the lateral force tend
to
opposite the slip_angle. the slip_angle could switch from -90 to 90.

But as we compute dynamic by interuption at 200hz, the oscilation is not
perceptible and
the model works well at low speed .
--
Seb
Game Developer
GPLRank -37.10
http://magicfr.multimania.com

I believe WSC will take the adaptation length into account.

-Gregor

...

Terminology quibble:
  Normal term for this in the USA is "relaxation length".

  Ok, this is what I'm doing as well.  I was really referring to slip ratio
(longitudinal, or rotational direction), where the denominator approaches zero.
 I've written a low speed model based on a torsion spring/damper that seems to
work well, eliminating the instability at low speeds, and also allowing the car
to stop on hills, as well as "pop back" a little when you stop.  Any tips on
this area?

  Also, I've looked and for the life of me can't figure out how to include the
relaxation length in a slip angle based model.  Any ideas?

Todd Wasson
---
Performance Simulations
Drag Racing and Top Speed Prediction
Software
http://PerformanceSimulations.Com