This is a trebuchet we made for our Concept Physics class. Our trebuchet threw a golf ball a distance of over 29 yards! We were the only all girls group in our class and we built the best trebuchet. We did a little bit of research and set out to construct our own and here is what we created!
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Step 1: Materials
7 - 4 ft long 2x4"s
2 - 2 ft long 2x4"s
4 - 3 ft long 2x4"s with the ends cut at 45 degree angles
4 - swivel chair wheels
1 - 2 1/2' re-bar
an eye hook
4 ft of string
1 laundry detergent basket
Step 2: Building the Frame
1) Make a rectangle out of two of the 4 ft long 2x4's and the two 2 ft long 2x4's.
2) Take two more 4 ft long 2x4's and center them so that they lie flat in the center of the 2 ft long 2x4's. This will create the platform that the golf ball will slide along before being released.
3) Attach the swivel chair wheels to the bottom of the four corners of the frame. The wheels not only help with transportation but also allow more force behind the throw of the trebuchet.
Step 3: Setting Up the Arm
1) Center two of the three remaining 4ft long 2x4's on each of the 4 ft long sides of the frame (not on the slide platform). Attach the boards vertically.
2) For extra support attach the four 3 ft long 2x4's to each side of both of the vertical 2x4's.
3) Drill one hole, large enough for the re-bar to fit through, on each of the vertical boards, one foot from the top.
4) Drill a hole in the last unused 4 ft long 2x4. Make sure this hole is large enough for the re-bar to fit through, too. This will become the arm.
5) Place the remaining 4 ft long 2x4 between the two vertical boards, line up the three holes, and place the re-bar in.
6) In our design, we held the arm in place with zip ties, but I'm sure there are better methods you could think of that would cause less friction if you were to re-create this trebuchet.
Step 4: Adding Weight and Sling
1) Attach the eye hook to the short end of the arm so it sticks out of the top of the board.
2) For our weight we used a laundry detergent bucket and just put the handle through they eye hook to attach it. That way we could easily vary our weight. The bucket also works well because the free moving handle allows the bucket to work with the law of gravity longer.
3) For the sling, cut the 4 ft of string into two 2 ft pieces. Attach one end of each piece to opposite sides of the sack. Attach a metal ring to the other end of one of the strings.
4) On the long end of the arm hammer in a nail at about a 45 degree angle into the end. This is where the string will release. We wrapped our nail in electrical tape so that the head of the nail wouldn't interfere with the release or the string.
5) Tie the string that is not attached to the metal ring to the top or the long end of the arm.
Step 5: Launch!
1) Add weight in the bucket. The ratio we found that works the best is 133:1, for weight in the bucket to weight of the thing you are launching.
2) Pull all the way back on the long end of the arm.
3) Load the sling with what you want to launch - in our case, a golf ball. Make sure the the sling is pulled all the way back so the inertia of the throw will keep the ball in the sack. Attach the hanging side of the sling with the ring on the nail.
4) RELEASE! (and get out of the way of the arm ;) )
Step 6: Results
Our trebuchet still needed a little tinkering on the launch day. I feel our data is not exactly representative of the potential of our trebuchet - if we'd had the time we would have adjusted the launch and point of release. Also I think we would add more to the weight to increase the velocity of the throw. But, that being said, I am still quite impressed with what it did throw. Our trebuchet threw a golf ball 29.3 yards and the ball had a peak acceleration of 292 m/s^2. Our trebuchet also threw the ball the farthest out of the rest of the class for trebuchets. Overall, this was a really fun machine to build. I think it worked better than anyone in my group thought it would and it was actually quite satisfying seeing a golf ball flung at high speeds for the first time, too :)