Making a Ballista

In my physics class we were assigned to make a siege weapon. I chose a ballista because I thought it would be challenging and fun.

The supplies we were given to use consisted of sturdy foam, wooden dowels/kabab sticks, hot glue, cardboard, popsicle sticks, and rubber bands.

First I started by trying to figure out how to get the arms of my ballista to rotate around an axis. To do this I sharpened the dowels and pushed it through the foam so the foam arm could rotate around it. I started out with two arms on each side but then I soon realized that it would work better with just one on each.

The next step was to figure out how to make the chamber where the dart would be launched from. To do this I hot glued one of the arms that I no longer needed to the existing piece that I created. It was finally starting to come together, but now the hard part. I had to figure out how to make the dart launch from my ballista.

I now had what was essentially the skeleton of the ballista, but now I had to make it work. It took lots of trial and error but I finally created a system of rubber bands that would powerfully launch the dart. After this I still had one problem, I had to make it fire consistently. To do this I added a trigger that the rubber band could lock onto so I could place the dart in the chamber with ease and fire when ready.