Large trebuchets were used as siege weapons to destroy castles and battlements throughout the Middle Ages. The design was originally created in China in the fourth century B.C., using manpower instead of a counterweight. In modern times, trebuchets are constructed for fun, as an educational tool, and for "chucking" competitions. You can make a small-scale trebuchet at home using PVC pipe and a few tools. All pipe diameters are 1" including connectors.
How to Build a Trebuchet with PVC Pipe
Place the two 12" lengths of pipe parallel with the two 5" lengths of pipe in between. The lengths of pipe will be arranged in a square.
Use four three-way connectors to form the square with the openings pointing up.
Fit a 1" length of pipe into each of the open spots on the square.
Place a 45 degree connector onto each of the 1" pipes with the open ends facing towards the middle of the square.
Fit a 10" pipe into each of the open 45 degree connectors.
Connect the open sides of the 10" pipe on either side with three-way connectors. The open sides need to point toward the center. Now, your trebuchet should look like two triangles next to each other.
Sand the ends of the 2½" lengths of pipe and cover them in PVC grease. Place these into the open spots on the three-way connectors.
Put the 16" length of pipe into the four-way connector. Slide the four-way connector down the length so that it stays 3" from the end of the pipe.
Use the rope or glue to attach the container that will be the counterweight to the side of the pipe that is 3" from the four-way connector.
Drill two parallel holes into the other end of the 16" lengths of pipe and thread the rope through them.
Grease the open ends of the two 2½" pipes and fit the four-way connector onto both of these. Your trebuchet is now completed. However you need to glue all connections except for the connections to the four-way connectors. This is because the strength of the structure is important to the workings of the trebuchet, while the four way connector needs to be able to freely spin.