1. Adams, D. A. (1971). Apparatus for providing energy communicating between a moving and a stationary terminal (U.S. Patent No. 3586413).
2. A Universal Joint (n.d.). https://en.wikipedia.org/wiki/Universal_joint#Universal_joint.gif.
3. Visualizing quaternions
4. null
5. Holroyd, A. E. (2019a). Lego anti-twist mechanism. Double version with lights. https://www.youtube.com/watch?v=1x_oQv_qj_U.