Algodoo

It doesn't power itself, but it does "run" without falling apart! Just don't accelerate it too fast, or get it running over 8.5 rad/s.

The pink hinge is only there for power, and can be removed at any time if you wish. The fixation holding the body up is also fine to delete, it just makes tihings much easier to have it on there.

Scene runs @480Hz. Could possibly run at a lower frequency, but it'd probably weaken the engine if you did so.