Fire Away
The goal of this project was to build a trebuchet and to get it to fire a clay ball as far as possible. While making our trebuchet, we had a few restrictions. The firing device would have to stay in the same place, and be able to be used multiple times. In its structure, it had to have a base that would sit on the ground, two arms that hold up an axle, and a lever arm with a load and effort end. It must be easily portable by one person and have no dimension that it longer than 1 meter at any point. In our first design, we had a 66.5 cm long firing arm, and the fulcrum of the lever was 29 cm off the ground with about a 1-8 effort-load ratio. We used 5 rubber bands to pull down the effort end. Our axle was made from wood and was roughly 7 mm in diameter. With this design, our trebuchet usually fired around 5 meters. We then ran tests and found what would be optimal in each of the fields I just stated. After these tests were run, we edited our firing device. After making our changes, our firing arm was 50 cm long. The fulcrum of our lever went up to 37cm, and we found that a 1-1 ratio is much better for distance. We realized that more rubber bands equaled directly to more distance, so we ended up using 10 rubber bands. To make sure our axle could hold all of the extra force being put on it, we got rid of our small, wooden axle and instead used a metal rod, with a diameter of 2 cm. After these changes, our trebuchet could fire about 45 meters.
Each group was tasked with testing and analyzing one variable, and my group’s variable was the length of the firing arm, and we found that a 47.5 cm long firing arm is the optimal lever length for trying to get the ball as far as possible. Through doing our experiment, we discovered that there is a balance, as the firing arm cannot be too long or too short. In our group, we tested the effect of changing the length of the firing arm, while keeping everything else constant. We did this by finding the ratio between effort and load of our first arm, and then we calculated the load and effort distances of the other arms. We then tested each of the arms three times, and found that, of the lengths that we tried, a 47.5 cm long firing arm was able to fire the furthest. The 34 cm arm we tried went an average of 11.5 m. The 35.5 cm long arm went, on average, 10 m. The 47.5 cm long arm went 13 m. The 51.5 cm long arm went 6 m, and the 66.5 m firing arm went an average of 4 m. So, as you can see through all of these numbers, the 47.5 cm long arm went the furthest by a good amount, making it the best choice for trying to go the furthest distance. Furthermore, the 47.5 cm long arm had two times when it went 14 m, which was the largest distance we got from any of our singular tests. We believe 47.5 cm is the best because it was in the middle of the lengths we tested, this makes sense with our results because if the firing arm is too short, there won’t be enough distance to get the ball going fast. Likewise, if the firing arm is too long, the effort side won’t be able to get the load end going fast enough to launch the ball at the top possible speed. While this could be remedied by adding on more rubber bands, that wasn’t the variable we were testing.
Final design:
Each group was tasked with testing and analyzing one variable, and my group’s variable was the length of the firing arm, and we found that a 47.5 cm long firing arm is the optimal lever length for trying to get the ball as far as possible. Through doing our experiment, we discovered that there is a balance, as the firing arm cannot be too long or too short. In our group, we tested the effect of changing the length of the firing arm, while keeping everything else constant. We did this by finding the ratio between effort and load of our first arm, and then we calculated the load and effort distances of the other arms. We then tested each of the arms three times, and found that, of the lengths that we tried, a 47.5 cm long firing arm was able to fire the furthest. The 34 cm arm we tried went an average of 11.5 m. The 35.5 cm long arm went, on average, 10 m. The 47.5 cm long arm went 13 m. The 51.5 cm long arm went 6 m, and the 66.5 m firing arm went an average of 4 m. So, as you can see through all of these numbers, the 47.5 cm long arm went the furthest by a good amount, making it the best choice for trying to go the furthest distance. Furthermore, the 47.5 cm long arm had two times when it went 14 m, which was the largest distance we got from any of our singular tests. We believe 47.5 cm is the best because it was in the middle of the lengths we tested, this makes sense with our results because if the firing arm is too short, there won’t be enough distance to get the ball going fast. Likewise, if the firing arm is too long, the effort side won’t be able to get the load end going fast enough to launch the ball at the top possible speed. While this could be remedied by adding on more rubber bands, that wasn’t the variable we were testing.
Final design:
- distance horizantal - 45 meters or 147.63 ft
- d vertical - 13.82 meters or 45.34 feet
- time in air - 3.3 seconds
- Velocity - 13.64 m/s or 30.5 mph which is as fast as a 4 year old greyhound from Utah, affectionately named Blaise
- V - 16.17 m/s or 36.17 mph, which is 9 mph faster than Usain Bolt
- total V - 21.15 m/s or 47.31 mph, which is about as fast as the fastest dog in the world, which was just as affectionately named Fanta
- Spring constant - 137.5 N
- Spring Potential Energy - 4.64 J
- Kinetic Energy - 2.9 J
- Release angle - 51°
Reflection
When the project started, our group was working well, but we weren't getting any good results. This time around, our group was able to both successfully split up responsibilities and have a consistent work ethic. We also had a lot of fun while doing the project, which made the whole process a lot more interesting. Our group was also able to effectively analyze the data that all of the groups had compiled, and apply it to our trebuchet. I was able to step back more and let myself be led by others, which isn't something I've ever really done in a group project before. However, as I said, our group wasn't able to get the results we had wanted on our first go. This was because we went for a somewhat impractical design, where me made the firing arm as long as we possibly could, which didn't work out. While we were able to work well together, and we ended up having very good results, we were also horribly inefficient, to the point where we would send one person to grab something, and then just sit and wait outside for them to come back. While we ended up fixing this, too, that doesn't mean that we didn't mess up. In the end, we had really strong teamwork, and a good final result, but made some silly mistakes along the way.