It was made in 1kb for the JS1K demo competition: https://js1k.com/2018-coins/demo/3124
Detailed source code: https://github.com/xem/epicycles/blob/gh-pages/index.html
Controls:
- Arrow keys: up / down to change the number of gears, left to toggle intermediate paths, right to clear the scene.
- Mouse: click to add points to the path