[ODE] Collision against static objects is not independent of mass?

[skjold@cistron.nl]

Hi Joe,

That's probably due to CFM. The heavy sphere does arrive at the same velocity, but since it's heavier it has greater momentum. CFM basically scales down the force that is required to prevent interpenetration, by the factor that you specify (at least that's how I interpreted CFM, but please correct me if I'm wrong).

If I recall, the CFM setting defaults to 1e-5 if you use floats, or 1e-10 if you use doubles (i.e. the setting with which the ODE library was compiled). What you describe isn't only there with impacting objects: Heavy objects that are at rest, are also pushing deeper into that ground plane than light objects, due to the tolerance CFM introduces.

Greets,
Mark


> Hi,
> 
> When I increase the mass of a sphere that I drop on a static (not connected
> to a rigid body) collider. The object seems to penetrate more than when I
> use a mass of 1.
> Is this a bug in ode?
> I mean they should reach the surface with the same velocity, so the initial
> interpenetration shouldnąt be higher. And since the floor should have
> infinite mass, the sphere should not behave different?
> 
> Joe Ante
> 
> 
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