Oh, YES! That is a cannon on the car, you are 100% right on that! And yes, you can absolutely blow up the robots with that thing! The cannon obliterates your enemies, so don't expect as much gears as from other weapons, however, BOOM, BOOM, POW!!! One more thing, the cannon is really strong, so don't be surprised, if you shoot a robot and it leaves a trail of broken enemies and obstacles!