Cannon

Today, our class received an assignment on cannons. Basically we need to build a cannon from a maximum of 5 pop cans and try to see which one will go the furthest. I do not know how we are supposed to make a base for the cannon if the tube thing is going to use 3 cans and only 2 left for the base. The cannon will be fueled with ethanol and the ball will be two Styrofoam cups taped together. Hopefully the cannon that we build will work.
Here's a HANDDRAWN picture of what the cannon will look like, (copied from the sheet).