Henry+and+Josh's+Trebuchet

= Henry and Josh's Trebuchet: = = "The Hurler"  =

Projectile - An object propelled through space with no capacity for self propulsion, in this case our christmas ball.
Projectile Motion - The trajectory of a projectile moving through space, determined by gravity and air resistance.

Air Resistance - The force of friction opposing the motion of our projectile in the air. When working with a 5 gram christmas ball this concept is crucial because the shape and mass of the ball only allow it to travel a short distance. As a general rule the smaller the trebuchet, the more efficient it will be.

Centripetal Force - The force of inertia that acts on the ball, related to the circular motion of the trebuchet arm. The force pushed out from the center of rotation, propelling the ball further.

Gravity - The force slowing down the ball and pulling it toward the ground.

Kinematics - The concepts of motion not relating to mass or force, used to measure acceleration, velocity, time and distance.

Building/Design Procedure
1. Our main objective was to create a lightweight, but efficient trebuchet. We stayed away from solid/heavy pieces of wood. Our base is a 24"x5" piece of hardboard. Hardboard is a high density engineered wood product. It is extremely strong and lightweight. 2. The two supports holding the arm are made out of particleboard. We cut two rectangular 15"x6" pieces. To save weight, we used a band saw to save off excess wood. We then drilled holes in both boards using the drill press. The holes is where the dowel/pivot point fits. 3. Next we cut the 1/2" dowel down to 6.5 inches. We then drilled a 1/4" inch hole in the middle and two 1/8" inch holes on the side. The middle hole is where our arm sits. The two side holes are for screws. The screws prevent the arm from moving side to side as it rotates. 4. The supports are attached to the hardboard by 4 pieces of 1.5"x1" pieces of spruce wood and 8 screws. At first we tried to use particleboard wood to save weight, but it was not strong enough. The wood cracked as we tried to drill the screws. 5. The 1/4" dowel is what we used for our arm. It is extremely lightweight, but strength was an issue. Our arm is 20" long. 6. We were afraid that our heavy 500g weight might snap our small, 1/4" dowel. We added a 4" piece of 1/2" dowel and drilled a hole in it and put it over the arm. We attached it to the counterweight side of our arm. 7. To keep the 1/4"dowel from moving around. We duct taped it to the pivot point. This also helped strengthen the arm by distributing the force evenly along the entire arm. 8. A screw was drilled into the 1/2" dowel so our counterweight could be attached to the arm. 9. The counterweight was tied to a 4" piece of shoelace which was tied onto the screw. 10. On the sling side of the arm. We took a 1/2" dowel and cut it to 1.5", drilled a hole in it and attached it over the arm, just like the counterweight side. 11. We drilled a screw into the dowel, so we could attach our sling to it. The wider dowel made it easier to drill a screw into the arm. 12. The fabric is 4"x2" and we sewed the corners together to make a pouch. 13. The pouch was attached to the arm with a 4" piece of string.

Materials
- Duct tape - Duct tape - and some more Duct tape - 36"x10" of hardboard - 30"x30" of particleboard - 20"x1" of spruce wood - Screws - Nails - 1 meter of 1/4" dowel - 1 meter of 1/2" dowel - 500g weight - 10" String - 10" x 10" Fabric - Shoe laces - Band saw - Miter saw - Belt sander - Power drill - Drill press - Robertson screwdriver - Ruler - Music to keep us awake

Testing Procedure
1. Measure arm length and weigh trebuchet 2. Load trebuchet with Christmas ball 3. Lower arm so counterweight is off ground 4. Release arm (let go) 5. Take cover (run away) 6. Measure distance traveled by projectile (if at all) 7. Repeat steps 2-6 eight times. 8. Adjust trebuchet to produce better results 9. Repeat step 8 many, many, many times.

Measurements and Calculations

 * Trial || Mass (Kg) || Arm Length (m) || Distance (m) || p=d/ml ||
 * 1 || 1.0 || .78 || 4.6 || 5.89 ||
 * 2 || 1.0 || .78 || 3.8 || 4.87 ||
 * 3 || 1.0 || .78 || 3.9 || 5.00 ||
 * 4 || 1.0 || .78 || 3.5 || 4.48 ||
 * 5 || 1.0 || .78 || 4.5 || 5.76 ||
 * 6 || 1.0 || .78 || 5.5 || 7.05 ||
 * 7 || 1.0 || .78 || 4.2 || 5.38 ||
 * 8 || 1.0 || .78 || 4.7 || 6.02 ||
 * Final || 1.0 || .78 || 4.05 || 5.20 ||

Counterweight
- Our counterweight acted as our stopper. We had to do several tests to determine how long the string had to be to stop the arm at the correct angle.

Weight Reduction
- We reduced the weight on our trebuchet by cutting off excess wood from the supports. We also cut off some of the wood from our base.

Sling/Pouch
- The sling was the hardest part to perfect. At first, we attached the sling to the arm with only one string. The ball would not stay in the pouch. Next we tried to place the pouch under the arm (so the pouch rests on the base, closer to the supports.) It yielded the same result. Our next solution was to use two strings to attach the pouch. We tied a string on both sides of the pouch so the pouch sits perpendicular to the arm. We added a nail to our arm. One string was permanently attached to the arm. We made a loop with the other string and put it on the nail, so when it fired, the string would slide off and release the ball. This solution worked very well. The ball stayed in the pouch and fired properly. We did several trials, testing the angle of the nail so the string would release at the right angle.

Christmas ball with string
- This was the best "sling." We tied a string to a Christmas ball and made a loop at the very end. We looped the loop around the nail and set the ball under the arm. The two string firing system had results of 2-3 meters. The ball with a string yielded results of 4-5 meters. This solved the problem of the ball falling out of the pouch.

Pictures
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