Algodoo

Automatic robot that senses the ground ahead of the wheel. If the ground drops away, then the robot reverses. It's a simple little task, kindof cool to watch.

Not my most revolutionary machine, but oh well.

Also, it will only work on pretty much completely flat ground, because in Ravenplucker's World everything is ideal.

EDIT: Also, it's grossly inefficient. I doubled up all the parts in a fit of sleep deprived brilliance to make it pretty and symmetrical. Kinda regret it now, maybe I'll redo it later.