Step 1: Materials and Tools
Tin (I used an Altoids Gum tin because it was small and compact)
Electrical tape (any tape will do)
Small piece of cardboard
Measuring spoon (or something similar)
Step 2: Freshen your breath...
Step 3: Making the tension arm....
You are going to bend the wire to fit as flush as possible in the tin, and have two notches on each side to hold the rubber band in place (see picture)
I used a pair of pliers and a small vice to get this step done. You may need to try a couple of times to get it just right.
Step 4: Cutting Spoons?
Step 5: Holding the arm in place...
To do this, cut a small piece of cardboard and wrap it around the base of the spoon. While still on the spoon, wrap a couple turns of tape for added strength.
IMPORTANT: Do not tape the cardboard to the spoon; you want to be able to remove the spoon. You want it to be snug but allow for movement.
Step 6: Getting ready to fire...
Insert the holder between the rubber band and start turning. Make sure you turn in the right direction or the catapult wont fire.
Step 7: Bombs away....
It may take several tries to get your desired settings. Your shots will depend on three things. 1) the size and weight of your ammo 2) the tension in the rubber band and 3) the length of the catapult's arm.
I got some pretty good distance after playing with it for a while, and it is good fun.
I also made some small targets that fit inside the lid for when I can't find anyone to shoot mints at.
Have fun, and please make or suggest improvements and post your pics. Be careful not to hurt anyone or give them fresh breath.