I saw an animated GIF of cogs inside cogs and decided to try to make my own version in Scratch. I hope you like it.
Coding by me. The project draws each filled black and white circle then adds little rectangles as the teeth on the cog. Version 2 - Better Math I hope! The Angle of a cog in its movement around the centre of its encircling cog, and the Orientation of the cog are calculated separately.