http://www.mujoco.org/book/XMLreference.html#CType What are the units for various values here? I found that mass was kilograms from another thread in the forum, but what about: body -> friction joint -> damping
The units everywhere in MuJoCo are whatever you imagine them to be. MuJoCo works with the numbers you provide in the model, without any unit conversions. It is up to you to specify everything in compatible units. The recommended units are SI.