Fw: [ODE] rolling contact force

[Michael Rauh]

> Presumably because the total velocity of the contact point is zero.
>
That's right.

> But the friction force is Ff = mu * Fn
> 
That's wrong. The *maximum* static friction force is mu * Fn. Only in
the case of kinetic friction, Ff is mu * Fn. Further info in the docs,
3.11.1, Friction Approximation.

Real rolling friction is completely different from (and can occur
additional to) Coulomb friction. It depends (among others) on the
deformation of the rolling body and the ground it's rolling on. See
for example http://hyperphysics.phy-astr.gsu.edu/hbase/frict2.html
(there are better sources certainly, but it was the first google hit)
for that.

> 
> In any case having to approximate rolling friction as damping, not because
> you're not wiling to pay the computational price for it but because the
> library design won't let you, is not very good, not even acceptable in some
> cases (I assume it won't be enough for accurate pool physics simulation for
> example).
> 

ODE is a rigid body simulation, so there is no way to simulate rolling
friction other than approximating it somehow. There are other
libraries that will let you simulate this accurately, but I don't know
any that won't have large demands on your purse.

Greets
Michael