Graham's+Trebuchet



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__ //Applicable Physics Principles// __
A trebuchet acts like a lever. Using the fulcrum (pivot point) this simple machine is able to move heavy objects with less effort. A trebuchet uses leverage the pivot point is approximately 1/5 of the total swing arm length. This means for every movement of the counter-weight portion of the arm the swing arm will move 5 times farther. 

//__Procedure To Build__//
At first, I had no idea how to begin on my trebuchet. I began doing some research and concluded that the optimum counter-weight size is approximately 133:1 and the pivot point on the swing arm is approximately 5:1. Next, I settled on the length of my swing arm to be 20” long. After, I drew up my design and began to cut the wood that I would use to make the trebuchet. For wood, I used a 2”x 4” ripped to ¾”x 2” as pieces for the base, uprights and swing arm on the trebuchet. Instead of using diagonal braces to hold the upright in place I decided to use twine connected to the base and put under tension. This was a way to keep the weight down on my trebuchet. I used glue and 4 screws to hold my trebuchet together. The counter-weight was made out of a piece of PVC pipe (filled with sand) with two caps on each side being held in place by a rod passing through the center of the pipe. The rod had a loop on one end so it could be attached to the end of the swing arm. The swing arm had a pin on the one end to hold the projectile. The point of release was adjusted by the angle of the pin on the swing arm. To find the optimal point of release it took many tests but was achieved in the end. The trebuchet I built did not use a sling. The ball was hung on the pin placed on the end of the sling arm.

//__[[image:Trebuchet_2.jpg width="267" height="275" align="right" caption="Trebuchet Being Assembled"]]List of Materials__//
1 – 20” x ¾” x 2” (swing arm)2 – 28” x ¾” x 2” (uprights) 1 – 38” x ¾” x 2” (center base piece) 1 – 32” x ¾” x 2” (cross base piece) 1 – 12” x ¾” x 2” (outrigger) 1 – 6” x ¾” x 2” (outrigger) 2 – 3” x ¾” x 2” (upright braces) 11 – 7/16” Nuts 3 – 5/8” Fender Washers 2 – Polyethylene End Caps 1 – Screw Hook 1 – Sewing Pin 1 – Empty Thread Spool 1 – 5g Plastic Xmas Ball Polyethylene Twine Approx. 17” of All-Thread Rod Approx. 10” of PVC Pipe Approx. a 4” Threaded Hook

[[image:Trebuchet_4.jpg width="300" height="223" align="right" caption="Trebuchet Pivot Point Assembly"]]//__ Procedure To Test__//
Once built, I began testing my trebuchet with a sling, but soon discovered that just the Xmas ball with a string worked a lot better. Next I began to test fire with many different weights of sand concluding that approximately 700g was the correct weight to get the most distance. Another problem that I faced was getting the release point of the Xmas ball just right. This was achieved by angling the pin on the sling arm forwards and backwards. Too much of an angle and the ball would smash into the ground a few feet ahead and not enough of an angle and the ball would go straight up in the air. After I had the angle and weight right I found that testing in my basement with a ceiling of 7 ½ feet was not going to work. Therefore, I had to brave the elements and go outside into minus 30°C to continue testing. After 8 tests the design proved promising.



//__Trebuchet Tests__//

 * Trial || Mass (kg) || Arm Length (cm) || Distance (cm) || P=d/ml ||
 * 1 || 2.4 || 58.5 || 800 || 5.69 ||
 * 2 || 2.2 || 58.5 || 500 || 3.56 ||
 * 3 || 2.3 || 58.5 || 600 || 4.27 ||
 * 4 || 2.1 || 58.5 || 400 || 2.85 ||
 * 5 || 2.5 || 58.5 || 750 || 5.34 ||
 * 6 || 2.4 || 58.5 || 900 || 6.41 ||
 * 7 || 2.4 || 58.5 || 1000 || 7.12 ||
 * 8 || 2.4 || 58.5 || 950 || 6.76 ||

//__Analysis__//
After testing my trebuchet 8 times, I concluded that the weight of the counter-weight should be approximately 133:1, which I had found out earlier to be the optimum counter-weight to projectile weight. I found that making your counter-weight heavier is not good because it actually causes the projectile to go a shorter distance. I didn’t use a sling to hurl the projectile because I found I could get more distance with just a string attached to the projectile.