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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

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.

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.