Using a custom motor during training with MJX

[jedi-alindogan]

Intro

Hi!

I'm a graduate student looking to use MuJoCo-MJX for reinforcement learning with a snake robot.

My setup

I'm using MuJoCo / MJX 3.3.6 (both), Python 3.10.18, x86_64, Ubuntu 24.04.

My question

I'd like to implement my own custom motor that is separate from what is specified for my robot's joints in the xml. I know that this can be done in mujoco with data.set_mjcb_control() but I can't seem to find a reference for how to do it properly in mjx and I was wondering if this feature exists and if there is an example of how to do this.

Minimal model and/or code that explain my question

I can include the asset and xml file, but its really not necessary--as the idea is to not use the motor model in the xml.

Confirmations

• I searched the latest documentation thoroughly before posting.
• I searched previous Issues and Discussions, I am certain this has not been raised before.