[ODE] Real rolling friction (again...)

[Dimitris Papavasiliou]

This came up in a recent thread but I'm reposting it as I consider it to be of 
some importance, not only to me but maybe to others as well.

Is there some way to model real rolling friction in ode? The approach used in 
the WIKI is physically wrong afaik. In fact, rolling friction is usually  
modeled just like sliding friction only with a different coefficient and it 
depends on the linear velocity of the body not of the contact point.

The problem is that since, in the general case, I do not know the normal force 
acting on the contact point nor can I calculate it I can see no way of 
implementing rolling friction on top of ODE. I have tried a few things but 
came up with nothing.  Is there something I'm missing?

If it is in fact impossible to implement rolling friction on top of ODE, how 
easy would it be to include it in the contact model?  API-wise all we need 
would be a couple more coefficients and a few bits in surface.mode to 
enable/disable it on demand.  This would be very useful since rolling 
friction is important in a lot of simulation scenarios and I see no reason 
why it's not in there allready.  The implementation should be quite similar 
to the sliding case, shouldn't it? (I tried looking at the code but couldn't 
make heads or tails of it. I'm not very familiar with the theory behind it 
I'm afraid).

Dimitris