[math-fun] Offset Somsky Gears

Dear math-fans, Here is a video of the Offset Somsky Gears: https://www.youtube.com/watch?v=ekZGCVFajqc People are asking me about the mathematics of Somsky Gears and the Offset Somsky Gears. Unfortunately, the math-fun discussions are private and unstructured. Is there any public explanation available? So far, I know only Tom Rokicki's Somsky Solver at http://tomas.rokicki.com/somsky.html. This is great for providing insight, but it does not explain how or why it works. Thank you. Oskar