[ODE] RE: Wheel rotation problem

Marco Grubert grubertm at hotmail.com
Tue Sep 10 23:39:01 2002

Hello Nick,

You beat me on posting my wheel questions by a few minutes ;)
My observations is that mass of the connected objects has a huge impact on
stability. I started out with a 500kg chassis and 15kg wheels. Reducing this
to 1/10th of the original value significantly improved the top speed when
wheel bending occurs. It appears as though the object mass would increase
with higher speed, pushing the wheels into a /\ shape when driving straight
or a // shape when doing a left turn. I have not yet tried moving the hinge2
anchor points around- does that make any difference?

> The user documentation suggests to use dBodySetFiniteRotationAxis() &
> dBodySetFiniteRotationMode() to fix this problem ... or to quote from my
> code below ... "Attempt to stop wheels freaking out".  I tried it and it
> 'minimised' the problem, but did not totally remove the 'bendy' wheels
> problem when cornering at high speed !?

I did not notice any difference when setting the finite rotation mode.
However, the documentation suggests setting the axis every timestep (which
you don´t do in the sample code). I don´t quite understand how this mode
operates or why the axis has to be reset. Why should it change during
iterations ?

> Actually I have not yet applied the finite rotation to my front wheels yet
> and sometimes my front wheels split in different directions ... see my
> art of the front & back wheels ... :-)

How are you adjusting the axes´ angles? I had this problem when only
querying one wheel, calculating the difference and then applying the same
value to both joints. Calculating the rate of change independently for each
of the two front joints fixed that problem.

  Marco Grubert