[ODE] slipping

[Arturo Colorado Garín]

>i wonder how can i find out whether the body is slipping on surface

I haven't done it yet but here's my guess (note: you're asking about 
slipping on a surface so I'm assuming the surface is static; but it can be 
extended to two moving objects easily): I would calculate the linear 
velocity of the point in the moving object that is in contact with the 
surface. Then, the object is slipping if this velocity is not equal to 0.

To calculate it, both rotation and translation must be taken into account. 
The linear velocity of the point in the object that is in contact with the 
surface is:

v_point = (w * dist) + v

where 'w' is the angular velocity of the body, 'dist' the distance from the 
Center of Mass to the contact point and 'v' the linear velocity of the 
(Center of Mass of the) body.

This is how I would calculate it in a real world problem but I'm pretty sure 
it needs some tweaks under ODE. For example, you might need to use a minimum 
value for the velocity of the point in the moving object to consider it is 
actually slipping.

Another question: Which contact point to use? I guess you can use any of 
them since the body is rigid, but again it might not be true with ODE.

Does anybody know if this would work? Any other idea?

--Arturo Colorado.