Algodoo

I combined davidz's Brownian Motor scene with s_noonan's ratchet script. davidz used a gear and a pawl to make a mechanical ratchet, but I wanted something that was a little more reliable and precise, and s_noonan's scripted ratchet was exactly what I was looking for. The "motor" isn't perfect. In fact it's rather erratic, but such a device can't work in real life anyways, because all of the energetic molecules that bounce against the rotor tend to cancel each other out. So, the statistical net effect is ZERO. But Algodoo never lets the impossible get in the way of a desired outcome!

EDIT - I forgot to explain the other major difference between davidz's motor and mine. His uses a spring to keep tension on the chain as it winds around the center spool. But the problem with that is, the tension on the chain increases as the chain gets shorter. Eventually, the "motor" doesn't have enough strength to overcome the spring tension. So, I replaced his spring with a sliding block that keeps tension on the chain via friction between the block and two rails. The rails squeeze against the block with spring tension. With this scheme, the tension on the chain is fairly constant, and only increases slightly as the block moves closer to the fulcrum (hinge). It seems to work fairly well.