Joseph Naberhaus

Trebuchet 2

Watch on YouTube

After building my first trebuchet I wanted to build something smaller. A >300lb weight box that can throw bricks is fun, but it is also makes it hard to use. For this trebuchet I used 110lb of tractor weights. This meant that I could pull the arm back with just my body weight.

Another big change was adding wheels to the bottom. The wheels help the trajectory of the weight box more closely approximate a straight vertical line which increases efficiency. Since the farm's ground is quite bumpy, I built a track for the wheels to roll on.

Efficiency

I was interested in knowing how efficient this trebuchet was. This would be measured in how much of the energy from the weight box is transferred into the projectile. First, I measured the distance the weight box falls. This was 3.5 feet (1.1 meters). The weight box is 110 lbs (50 kg on earth). Therefore, there it's potential energy is given by:

The trebuchet could throw a 16 oz (0.454 kg on earth) croquet ball with a range of 250 feet (76 meters). By analyzing the video I determined the angle of release was 55 degrees. Then I solved the range equation for velocity:

We can use that velocity to determine the energy of the croquet ball when it is released:

Therefore, the total efficiency of the trebuchet is about 33%.

Future Plans

• Shorten the sling and compare range
• Make a leather poach that doesn't let the projectile slip out of
• See if I can reduce the friction between the axle and the arm (ball bearings?)
• Throw firecrackers
• Throw road flares