To fire the trebuchet you draw down the swing arm, put the pin in it ( My pin is on a long string so I can stand back from it. Lay out the string pouch on the base of the trebuchet, put in the projectile and hook the ring of the string over the headless nail on the swing arm. You are ready to go. All you have to do is pull the pin and watch the thing shoot off like a fire breathing dragon. This thing is powerful because of the efficiency of the axle and the sheer weight of the bowling ball.

Here is my bicycle wheel trebuchet in the cocked positon and ready to fire. Now if you make this project don't fire it in the house! Take it outside.

Watch the video!

Some Trebuchet Tips and Hints

Remember: Safety is everything! Wear safety glasses when building and when firing your trebuchet. This thing is powerful! And if you are under 18 get an adult to help you or to give you permission and to oversee everything. Especially if you are using power tools. And never use anything dangerous as a projectile - I recommend only using a wadded up ball of masking tape.

About the axle, fork and bowling ball: You don't have to use any of these items. The whole point of this project is to show some creativity and what is possible with just items around the house. Be creative!

Take your Time! This project took me two days to complete - mostly because my first two designs broke! If you make your trebuchet using bolts and good solid pieces of wood you should be able to make it in one day.

About the trajectory/ distance and height of your projectile:

There are three main factors you can adjust to change your trajectory and speed. The first thing is the weight of the counter weight. A heavier counterweight will generate more force and throw the ball further. The second is the angle of the headless nail - this is a big factor in distance. Tinker with this nail. The third factor is where you place the axle in the swing arm assembly. Moving this will affect distance. I placed mine at the 1/4 point. So on a four foot swing arm it is one foot from the end and this works pretty good.

This project a bit too ambitious for you? I have a smaller trebuchet project called "The Little Dragon" it is a table top size and it really works outstanding The Little Dragon Trebuchet Project