Hello all, A great advantage or strength of OpenSim is the biomechanically consistent human models. As the model of OpenSim is in .XML file format, I guess it would be possible to import the OpenSim models to MuJoCo, which also uses XML file format. I wonder if anybody has written a code to interpret OpenSim XML file format to convert it to MJCF or MuJoCo-style XML file format. Please let me know if you know any work done ! Thanks!
Tom Erez attempted to write an automated converter a while ago, but it was hard partly because the OpenSim XML format was not very well documented, and the conversion needed manual cleanup. I agree it would be nice to have such a tool, especially since MuJoCo simulates spatial tendons very efficiently. Below is a screen shot of a lower-limb OpenSim model which Tom converted to MuJoCo (tendons only):
Very great! I'm actually working with Prof. Hogan at MIT as a Ph.D. student, and we might put some effort on this work as well. Is anybody continuing this work? - we would be very interested in this sub-project!
Not that I know of, but feel free to get in touch with Tom Erez. He is at DeepMind. It is possible that the OpenSim XML format has evolved and building an automatic converter has become easier. Attached is the XML that Tom generated at the time (you can simulate this in MuJoCo 1.50). If you are going to simulate muscles in MuJoCo, note that it supports actuators with first-order activation dynamics (mjData.act variables). When I was designing MuJoCo, a major goal was to make it useful for biomechanics and motor control. Later the emphasis shifted to robotics and machine learning, but the core elements are there.