I'm trying to get an answer for something potentially quite simple, but I can't visualize it (nor do I have the parts yet to build it). It's for a little hobby project, but I'm slightly concerned I have made an assumption about what will happen, which may not be correct. I've drawn the problem below.
In essence you have two pulleys connected by a timing belt.
Pulley A = 80 Teeth Pulley B = 120 Teeth
Pulley A is static, it does not rotate at all. Pulley B is free to spin around its own axis. It also then rotates around the axis of A, keeping the timing belt taught.
In one revolution of pulley B around the axis of A (dotted line), how many times would pulley B have rotated?
My assumption would be that it would be 2/3 rotations of pulley B for every time it does an entire revolution around pulley A.