Algodoo

Using my small scale Ross Yoke spring engine, but with a little extra oomph. I very rarely make cars on the scale this works with, so I won't use it much.
However, you folks might.

Just stick it in a vehicle, hook up the orange disc to the drive train, and you're good to go.

Press Q to get it going Clockwise,
and A for anti-clockwise.
Press Z to stop the engine.

There are 5 gears, each on a toggle, from 1 through to 5. - Be sure to deselect the current gear before changing.

- Fixed it up and improved:
Applied a Resonance Brake to 5th gear, stablised the disc assembly, added 2 more engines, provided a free engine above, with the springs needed to connect it to the system, and tuned the engines up just a bit more.

(Just C&P the engine & springs into place, and then take a copy of the little orange connecting rectangle and bolt it on.