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In addition to SmoothSphereHalfSpaceForce, can other types of contact forces be tracked in Moco ? For example, in the process of going up and down the stairs, it is obviously inappropriate to use SmoothSphereHalfSpaceForce.

Hi Jingke,

SmoothSphereHalfSpaceForce is the recommended contact force element to use in Moco, since it is smooth and differentiable. It is possible to use other contact models, but most others supported in OpenSim will need to interact with a half-space plane in the same way and therefore will also not be suitable for walking down stairs.

If you only want to simulate a single step-down task, you could have two half-space contact geometry elements: one for each foot. Beyond that, we would need to support more complicated contact geometries that are not limited to half-place contact. One possibility would be to have a contact geometry element that is locally a half-plane, but the half-plane definition could change based on the location in ground.

-Nick