Modelling Joint-Motor Couplings via Tendons

Omniverse Isaac Sim
1

Hello everyone,

I have a question related to the modeling of two coupled motors in IsaacSim.

In MuJoCo, I can model two coupled motors (let’s call the m0 and m1) that drive two joints (let’s call them j0 and j1) via two tendons, each of which is connected to the two motors and one of the joints.

I am, however, having trouble creating such a setup in IsaacSim, since there seems to be a requirement that Tendons can only link joints in a tree structure with each other.

However, in my setup, the motors would actually be decoupled from the robot joints (i.e., they would be in different subtrees). I already read here that this may only be a limitation of the USD parsing API and not of IsaacSim itself. Unfortunately, the URDF importer fails on my MuJoCo XML file (although I can simulate it with MuJoCo without any problems) such that I cannot “reverse” engineer a solution in that way (if one exists)

So I wonder whether it is possible to specify said coupling, e.g., via the Python API.

Best Regards
Pascal

2

Hi Pascal,

If you have joint drives on both j0 and j1 I would suggest mirroring the drive targets instead of using tendons.

Alternatively, you could use a gear joint if the two target joints are revolute: Rigid-Body Simulation — Omniverse Extensions documentation

Philipp