Algodoo

This is a spring engine I made using two pistons attached with a spring. Because the pistons oppose each other, they cancel each other's motion out, which makes the motor pretty stable. I also designed a throttle mechanism that automatically returns to idle after a few seconds. It idles at ~350 rpm and revs up to ~750. Controls are:
Enter to toggle the brake to stop it
Shift to start it
Up arrow to rev it up