The Hila Trebuchet

Designed by Wayne Campbell, Hila Science Camp

Short Video of the Trebuchet in Action (Windows Media Player)

Video discussing the science behind this trebuchet.

The trebuchet is a medieval machine designed to hurl objects into the interior of castles under siege or even knock down castle walls.

Our model trebuchet uses a swinging counterweight, instead of the simpler fixed counterweight.  The swinging counterweight, though more complex to build, transfers more energy to the projectile.

Parts and Overview:

Build the counterweight basket:

Attach uprights and build base:

Construct the sling:

Final assembly:

Using your trebuchet:

Link to trebuchet physics: (Word Document)

What of the swinging counterweight configuration? A detailed analysis of this configuration is left for our upper-division mechanics course, but students at the introductory level can appreciate the essential results. Consider the motions of two otherwise identical trebuchets, one with a fixed counterweight, and one with a swinging counterweight. Both counterweights liberate the same amount of gravitational potential energy. However, the fixed counterweight transfers some of this energy into rotational motion as it is constrained to move about the throw arm. The swinging counterweight falls nearly straight down, without significant rotation, and has very little kinetic energy as the projectile is released. The swinging counterweight transfers more energy into rotational kinetic energy of the throw arm and thus the projectile.