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Catapult Project
Trebuchet Model

Materials needed

Try to find things at home first. Any extra wood, nails, etc. will be useful. The trebuchet doesn't have to be fairly large. If made correctly, it should fire very accuratetly.
It works using rotational motion. There will be a small hook on the end of the arm to slip the string over. Hopefully, the hook can be adjusted to different angles. The metal ring slides onto the hook. The ring is attached to a string, which is attached to the tennis ball. When the counter-weight drops, the arm will rotate, and the metal ring will release, thus launching the tennis ball.

Follow the diagram to build the catapult. Make any adjustments if necessary.

Update: 2/25/04
Upon testing, it turns out that a sling is very difficult to use in this trebuchet. We may have to launch the tennis ball AND the pouch together in order to achieve maximum distance, as well as accuracy. One thing that worries me, is that the air resistance of the pouch will slow down the projectile.
The more mass the counterweight has, the farther the projectile will fly. Adding weights significantly increases the performence of the trebuchet. My small model can launch a small object at least 3 or 4 meters. I am aiming to get the bigger model to launch the tennis ball at least 10 meters, to a maximum of 20 meters, which I feel is not that easy to achieve. 30 meters may be out of the question. Hitting the wall is insanity.
Wood for the arm has been cut today. The wood is about an inch wide, a quarter of an inch thick, and 4 1/2 feet long. I plan to layer two pieces of wood at the fulcrum to increase strength. I took a plastic container and put rocks in it to make the counter weight. It weights at least a couple pounds. If we need more weight, I have some heavy metal parts. As of right now, I have basically all the materials needed to build this trebuchet. I don't have a metal rod though.

I plan to make a chart listing all the data. The angle of the hook will be adjustable, and I will make a table of all the main angles and the distances that are launched. I am not expecting this thing to go farther than 20 meters (about 60 ft).

Update: 2/26/04
I tested my trebuchet again. This time, I used a sling. The projectile went considerably farther. The catapult launched rocks on average farther. The main reason is perhaps air drag caused by the sling. A small rock can be launched at least 20 feet (6 meters), if the angles are right.
Also note that any interference at all with the arm during the rotation, will cause significant skewing of results. You want to limit the amount of interference with the arm. Meaning, you don't want it bumping into things. Once again, the mass of the counter-weight must be very large. More than 2 pounds might suffice, but I don't know. My mini trebuchet has a counter-weight that is about one pound.

Update 3/01/04
Ok, the wood is now being cut as we speak. There are a total of NINE (9) pieces, not counting the base blocks. Two pieces will be VERTICAL SUPPORTS. They will hold the ARM. Four pieces will support the vertical support. The other three pieces go on the bottom. They are supposed to keep the thing together.
The counter-weight right now has a weight of about 7 pounds. I'm not sure if that will suffice.

© 2004 Robin Hu