A Trebuchet
Building a Trebuchet
Design
We’ve had this technology for centuries. How hard can it be?... Well, as it turns out, pretty difficult. My goal was to launch a baseball the length of a football field. To reach this, I needed to know how far a baseball would travel with air resistance, how fast the trebuchet would launch it, the structure’s dimensions to withstand the forces, etc… It was an ordeal.
Manufacture
When I began this project, I had very little wood working skills, almost no tools, and I was living on the third story of an apartment building. Not ideal conditions for building a trebuchet. Trying to discreetly cut lumber using your engineering books as a chopping block makes for a tough time. It was a slow process building this trebuchet, but I learned many new, hands-on skills.
Performance
Seeing a project you’ve spent months on finally working is a unique feeling. Inevitably, the first launch never works perfectly. After designing and manufacturing, there is still plenty of work to be done. I had to add minor tweaks after each test launch: redesigned projectile pouch, adjusted sling length, extended launch pad, etc. The joy after the first successful launch though is priceless.
Design
Manufacture
![Don't have a chopping block? Just use your largest engineering book.](https://images.squarespace-cdn.com/content/v1/6026bee5111da040bd1fe57e/1613614013810-D105QDCG9O0THL7F9JOC/IMG_0392.jpg)
Don't have a chopping block? Just use your largest engineering book.
![Launch arm. The neighbors didn't seem overjoyed during this process..](https://images.squarespace-cdn.com/content/v1/6026bee5111da040bd1fe57e/1613613972471-RF34CM8CVTPFSEF5B8AC/Launch+Arm.jpg)
Launch arm. The neighbors didn't seem overjoyed during this process..
![Counterweight](https://images.squarespace-cdn.com/content/v1/6026bee5111da040bd1fe57e/1613613951564-4YNDYN668G6GO9XZCRIQ/Counter+Weight.jpg)
Counterweight
![Launch finger](https://images.squarespace-cdn.com/content/v1/6026bee5111da040bd1fe57e/1613614093804-KQT5PP3EPHTL8NJMZG3R/Launch+Finger.jpg)
Launch finger
![Frame](https://images.squarespace-cdn.com/content/v1/6026bee5111da040bd1fe57e/1613613990109-WEDWF6B5J3HK2LBVZP6R/Frame.jpg)
Frame
Assembled
Performance
Theoretical v Reality
The results from my model for the trebuchet motion gave an expected release velocity of 90 mph. By counting frames and using known distances, the measured release velocity was 88 mph. Pretty close. My model for a baseball flying at 88 mph launched at 34° predicted a flight distance of 311 ft. The measured result was 235 ft. Not as close… but aerodynamics is a very complex subject. Overall, I was excited with my creation and impressed by my models. A 2% error for the projectile release velocity is nothing to sneeze at.
Skills Used During This Project
Engineering
Lagrangian Mechanics
Euler’s Method
Runge-Kutta, 4th order
Shear Force and Bending Moment Diagrams
Excel / Excel VBA
Manufacturing
Woodworking: circular saw, drill, clamps
Knots: adjustable grip hitch, bowline
Sewing
Installing grommets