Anisotropic friction

[Sietse Achterop]

Hallo,
I need to create anisotopic friction, so friction that depends upon the direction of force.
Concretely, imaging a box on the ground that has friction in one direction (X) and little or no friction in the other direction (Y).
Is anything currently possible in opensim, or do I have to create a new friction model?
Where would be the best place to start?

Thanks in advance, Sietse

[Thomas Uchida]

You could create your own friction model. Another strategy that might work is to change your model topology to ground -> prismatic joint in X -> massless body -> prismatic joint in Y -> box, and add an ExpressionBasedCoordinateForce (https://simtk.org/api_docs/opensim/api_ ... Force.html) to the coordinate associated with each prismatic joint and use a different expression for each direction.

[Sietse Achterop]

Thanks for the idea.
But the friction should also dependent upon the Z coordinate. The friction plane has to be lifted off from the "ground/water" and then there should be no friction at all. We'll see.