contact problems in MJX

[gautica]

Hey, I found there is some contact problems in MJX. I am using PD control to make quadrupeds stand at default joint positions. It works fine in Mujoco, but with the same setups (stiffness, damping) it doesn't work in MJX. I rendered the contact force, and it seems the contact force is changing kind of randomly, even the robot just stands there. This happens when impratio is large impratio="100", but a small impratio makes it slippery, the robot cannot stand there too

Here is the video of it. The robot should just stand there. Thank you for any help.

https://github.com/google-deepmind/mujoco/assets/33986182/8c40165e-ee44-4d67-be30-f52ec325121c

[btaba]

Hi @gautica , can you send us an XML so we can debug? Likely you'll need to tune the solver params, see https://mujoco.readthedocs.io/en/stable/mjx.html#performance-tuning

[btaba]

There's an MJX version of the go2, so closing this issue. PTAL at https://github.com/google-deepmind/mujoco_menagerie/tree/main/unitree_go2