you also might be better off using some sort of pneumatic piston for the break pedal control, because I don't think a servo would be able to push a drum break setup well enough to stop a cart, also you might want to use a very large servo for your steering, or attach some form of gear to the wheel and use a large reduction on it. and make sure you set up some form of emergency fail safe, if you suddenly lose connection while gunning it, it might continue to just keep going till it hits something or someone, or runs out of gas, or flips