Algodoo

The credit for this should really go to Paradigm 29, as he designed the cannon and chassis. All I did was join them together into one unit.

Controls are simple. Left and right arrow keys to move, up and down to aim. Press enter to fire and S to slow down.. The chassis also comes with its own thrusters (Q left, W up, E right) for navigating more difficult terrain.

Edit: Added some hills to try it out on, as well as a tower at the end.