While I was in high school I have constructed a number of catapults for the Science Olympiad team. I generally liked more to design them than to actually build/use them. Nonetheless, by the end of my senior year I have constructed over 15 separate devices.
Here are blueprints for some of those catapults. Make sure to read the attached readme's before using for your purposes.
Hatra Ballista (0.94 MB) - Plans for the hatra ballista device. Won the gold medal during the Massachusetts State Science Olympiad of 2005
SiegeLord VII (0.69 MB) - A curious device that graced the National Science Olympiad of 2006
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