Hello, Emo, Although we have a nice documentation for MuJoCo, I think it is often confusing and hard to fully understand it. At this point, I think that if you could provide us with a reference textbook that you mostly refer to for building the MuJoCo, that would be awesome for the users to quickly understand the notations (and mathmatics behind). I think I have seen somewhere in the documentation that R.Featherstone's 6D kinematics is useful but I'm not sure.... I would greatly appreciate if you reply to this post with the reference!
There is a list of references in the documentation here: http://www.mujoco.org/book/computation.html#References Featherstone's book is the best reference for multi-joint dynamics. The treatment of contacts and other constraints is based on my own work, and I never wrote a textbook on it, so the best source is the Computation chapter in the documentation. A brief version is available in this paper: Convex and analytically-invertible dynamics with contacts and constraints: Theory and implementation in MuJoCo Todorov E (2014). In International Conference on Robotics and Automation