My husband made a cannon launcher. Supplies needed: 4 inch PVC pipe, clamp, black industrial strenght glove (from Dollar Tree) and styraphome balls from craft section (used to make ornaments), black spray paint.
Put a toothpick in the balls so that you can hold them to paint. Spray paint black. Assemble cannon and paint black. He tied the fingers of the cannon with string so you could grab the whole "knot" to pull back and launch the cannon balls.