Algodoo

energy in the purple flywheel gets transferred through the small green wheel to the blue wheel, depending on the angle of the pink wheel. the timing is set up so that power is put into the blue wheel only when it's turning in the right direction such that application of such power increases the angular velocity of the pink wheel.

or if you don't care about any of that, you can just watch it spin :3

ASD to control purple flywheel