rec.autos.simulators

by **Gregor Vebl** » Sat, 17 Nov 2001 17:48:23

> Adding it to the other forces (F_long=pacejka_Fx(SR,...)) is where I
> go wrong. Must probably always counteract the F_long (so if F_long>0,
> F_damping<0 and vice versa).

The above sign seems to be a good choice, but it looks as if you have an
opposing frictional type of force which cannot be completely stable (it
will jitter from positive to negative).

I have another damping force (actually, just a damping torque) in my
system for the longitudinal dampening, and while I can't remember all
the details about its size (indeed some sqrt of inertias and tyre
stiffness occur in it), the only thing I know is that I make it
proportional to dSR/dt, so it is 0 in stationarty state. Perhaps that's
an idea to consider?

-Gregor

by **Ruud van Ga** » Mon, 19 Nov 2001 04:13:27

On Fri, 16 Nov 2001 09:48:23 +0100, Gregor Veble

>> Adding it to the other forces (F_long=pacejka_Fx(SR,...)) is where I
>> go wrong. Must probably always counteract the F_long (so if F_long>0,
>> F_damping<0 and vice versa).

>The above sign seems to be a good choice, but it looks as if you have an
>opposing frictional type of force which cannot be completely stable (it
>will jitter from positive to negative).

Perhaps, but if I include velocity reversal checks in it, it might be
fine (after all, it's only used at low speed). So if the damping+other
forces makes the wheel swing the other way, I keep the position locked
and set spin acceleration and velocity to 0.

Hm, sounds a nice one that also goes down to 0 at low speed. I'll have
to implement it to see.
First I want to get some ODE tests in though, before I get diverted.
:)
BTW The AABBTrees work really nice; use it for carbody-track triangle
collisions now and most of the time I don't even check 1 triangle
anymore, as the car floats above the surface (so in the end, you'll
end up in an AABB that is the track, and since the body is almost
always *above* the track, they never intersect and no polygons are
tested; you just gotta love those O(logN) trees. :) ).

Ruud van Gaal
Free car sim : http://www.marketgraph.nl/gallery/racer/
Pencil art : http://www.marketgraph.nl/gallery/

rec.autos.simulators

Car physics: road reaction force

Car physics: road reaction force

Car physics: road reaction force