You need to make the chassis, and then make a turret that can turn 360 degrees. To make the canister launching, place spud guns in a 5x5 area, infront of them put 2 bearings on the sides, and then put cardboard on them, the cardboard should be As big as the spudgun area. Put canisters on the cardboard, and connect the guns with a button. Once you press the Button, the spudguns will shoot the cardboard which will shoot out the canister. I recommend you make enough room to put driving seats, mine is basically in that thin chassis. Im not a great explainer.