Torsion_friction and rolling_friction (PhysX backend)

In RigidShapeProperties we can set the torsion_friction and rolling_friction. What is the meaning of these two parameters and when do we need to set them?

Get an answer from ISAAC developer Kier Storey, Thanks Kier!

The rolling_friction is not used in Physx, so it will take no effect whatever the value, just ignore that when you are using PhysX.

For torsion_friction, it is a resistant torque when rotating a rigid body against a surface. A more detailed explanation of this property in physics can be found here. In PhysX, torsional friction is implemented via a patch friction model, where torsional patch radii are used to approximate the surface area formed by a single point of contact. So normally we do not need to set these parameters it two geom can form contacts with multiple contact points. It is corresponding to the patch radius in PhysX. From personal experience (maybe not true), setting it to be 0.05 can already improve the stability of robotic grasping a lot.