The summer after my freshman year, Kerrie W. and I built a 28 ft. tall trebuchet to launch water balloons, confetti, fruit, [whatever we wanted to launch] as part of an amusement park party for our dorm. We worked with a more senior engineer, Lauren S. who was very helpful in teaching us the ropes as we were but kid engineers.
From March to September of that year, the three of us worked on bringing this project to life. I was in charge of CAD'ing and executing the pivoting arm portion of the trebuchet. I CAD'ed the arm in Solidworks and worked closely with Kerrie to make sure it would interface well with her base design.
We created a bill of materials, and planned to build the project in a one-to-two week span in August. We had very little practical engineering experience, so Lauren handled a lot of the calculations and taught us the basics in the process. I remember trying at some point to run a dynamics calculation to see the motion of the arm with different loads on it, but we were hung up on lack of information on the bearings - without an idea of the coefficient of friction on the bearing we couldn't have faith in the simulation or results from our equations of motion.
Ultimately we would test it and see that it worked, and find the oscillation in practice.
We built the project with the help of many friends over the course of 2 weeks, and it was operational!
The coolest part of this project was learning all about suspension systems and ropes as we used lots of ropes to assemble the arm on the pivot at 12 feet above the ground, and made ground anchors to built a rig for loading the arm before launching. Weirdly, we never took pictures of the attraction with the bucket on it, but we launched water balloons and various food-stuffs and a computer someone was generous enough to donate to us!
The Solidworks drawings submitted to MIT's EHS department, and some renderings of the CAD we constructed.
photos of the build process, featuring lots of drilling and figuring out how to fasten things with 18" bolts.
