The Proof of Efficacy document can be found HERE.
We have finally completed our brand-new project! It was called Fire Away! The project was that we would make a trebuchet that launches a projectile as far as possible while fitting into a 1x1x1 meter size, with two legs and an arm. This project went through its ups and downs, with our prototype destroying itself on multiple occasions, our class setting off the school fire alarm, TWICE IN ONE PERIOD, and we finally finished with a great design. Let's go!
The road to wisdom? Well, it’s plain and simple to express: Err, and err, and err again: but less, and less, and less.
Piet Hein
Step one was how we were going to design our machine. We 3d modeled a basic idea in Sketchup, and we made our prototype. Our prototype was simple and inefficient. We had a base with two legs made of wood. The arm was held by a PVC pipe that was put into 1cm deep holes in the legs, which the PVC pipe would slide into and be able to swing around. This was a very inefficient way of doing this because of friction, but more on that later. The arm was attached to 3-4 rubber bands on the base. The rubber bands were our potential energy, as a human would push down on the other side of the machine, stretching the rubber bands, and then release, firing the ball that was loaded in a .5cm deep hole in the arm. A simple prototype.
This prototype worked, but it had some limitations. The first limitation was how we attached the arm. We needed to be able to take it on and off for storage, so the arm was smaller than the length needed to go fully into the 1cm holes on the legs, causing it to fall off whenever we stretched more than 30°-35° back. Another issue was my human mess-ups. We decided to drill the files 3 centimeters below the tip of the legs, and while they looked like the same height to the naked eye, they were most certainly not. I drilled the holes 3cm, the same on both, but they did not align, as the second leg's hole was too high for the PVC pipe to go straight in. We found a workaround that would come to bite us in the rear end, by making the hole tilted to accommodate for the small height change. This was what made it difficult to keep it in for a 35° shot, which most of our shots ranged from us pushing down 35° to 45°. We knew that we had to deal with this in our final build. We ended up fixing that in our final build and also the friction issue with the same stone!
After learning from the sloppy design of our prototype, we made sure our final build was made well without the sloppiness of our prototype. The final build used a long, thick base to stop it from falling over due to Newton's third law, our arms were higher this time to have a longer arm, and drilling completely through the wood so that the ends of the pipe were on the other side of the arms, reducing the friction, and also have nothing attached to the pipe so that the arm spins on it freely so that the arm does not have to move with the pipe, cutting down on friction again.
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