While I’m at it—here’s something else which initially looks impossible until you work out the basic principles behind it. Which I’m sure you can. 😉 Having written about the levitating Slinky earlier, I’m not going to write another 1300 words now explaining that the radius can vary how you like provided the combined radius of the two gears is always equal to the how it works.
Just some wooden gears. The wheel, reinvented.
The Other Blog Without A Name 