We built a catapult out of things we found in our garages, and bought a few things. It is a decent size, 2 ft by 3 ft, and a basic wood structure. Nothing impressive, right?
Turns out, no. When we used latex medical tubing as the spring force, the catapult started launching tennis balls up to 40 meters away, and with enough power to: 1, bounce the arm off the front hard enough to send it back over to launch position, and 2, rip the basket apart 3 times. We had to build a almost-solid duct tape basket, put a pile of foam at the front, and be generally more careful where we pointed the catapult.
Now we get to where we start snapping hooks. On the day before our school Maker Faire, we test launched the catapult. The ball soared 50 meters away, and we lost it in the street. When we got back to the catapult, we found that our first hook got snapped off and got flung 15 feet behind the catapult.
On the day of the maker faire, we got a new hook, tested it, and it promptly snapped. We got another one, and it also promptly snapped. Finally, we had to use a already half-broken hook, and then one of our groups dad cane up with a new, extra thick steel hook that we could use, just as the broken hook got pulled out.
The 5th hook held, and worked for the rest of the day. Overall, we found that strong springs on a catapult are cool, but you need to make sure that your hooks can support it.
--Team of 7B-9