Strawbees are plastic pieces that can be used to connect standard size drinking straws. At a local Hack Space we tried to build a catapult with these connectors, straws, rubber bands and other miscellaneous items.
My design is a ballista (closer to a crossbow in design than a catapult)
Step 1: Main Beam
The main structure consists of 5 equal length straws joined at both ends with a 5 joint. This provides significant compressive strength.
Step 2: Side Support
Two straws are inserted at one end and spread to form a triangle. At the front they are connected by another straw.
Step 3: Legs
The legs at the front serve mainly to raise the front of the ballista to the correct height. They do not provide structural support.
Step 4: Rubber Band
One or more rubber bands can be hooked into the main beam. Firing is done like a slingshot: The projectile is lodged at one end, pulled back and released. A golf sized airflow ball was launched approximately 10m on the first shot.