I have made a knex trebuchet which is about 3 feet in length and 2 ft in height.
The frame is strong.
It can fire quite far but I'll get measurements tomorrow
It can fire anything that fill fit
unfortunately it doesn't use weights as a power source due to having nothing that could be heavy enough to fire it so, I put loads of rubber bands on it. its fire using string which is attached to the projectile and the other end of the string is connected to the arm which when is up right the string detaches and the projectile is released. At the moment is can fire about 20ft and gets loads of air time.
about posting this:
I will test it tomorrow and iron out any problems and make it perform better. after all of that I will post it.
I think this is the best trebuchet to be posted :)