Algodoo

A finely balanced pendulum. Powered by a single thruster. A perpetual motion that does not accelerate over time.

Just enough power to keep it swinging, but only in one 360 degree direction at a time. To make it swing clockwise you'll need to flip the direction of the thruster. If set to less than a full revolution it will gradually slow down due to the thruster working against itself for half the cycle.