Need advice : Building a Catapult

[teh1337tim]

Hello my dearest europa barbarorum history geeks and gamers...

I have long played EB and other historical games and have now came to you geniuses to help me in a school project.
We're tasked to build a catapult style weapon that can launch objects 10m - 50m
Restrictions are a 75cm in height and width (to get in classrooms and past doors)

We of course have to build it ourselves and as such, I'm here asking if any of you can point me to any sources that can assist me.
Of course this must not be over complex as my two partners are females... (basically im doing all the work lol).

I've looked up at designs from the Warring States period, Han, Tang and others eras in china and Medieval Trebuchets and onagers.

Any help is much appreciated... oh and I'll post pics once this project is complete.

Tim!

:')