Trebuchet Project By AM and CS

Introduction Inquiry Statement: Historical technical innovation has contributed to advances in modern day human progress. Global Concepts: Scientific and technical innovation. Design Specification: Students will design and build a trebuchet that is capable of throwing an object with repeated accuracy. IB Design Cycle

Investigation

Pros and Cons The swinging counter weight Vertical counterweight Easy to adjust Cons: Possibly difficult to move? The fixed counterweight on a fixed frame Pros Easiest to build Cons Shakes frame Non-vertical fall Not as efficient Difficult to adjust The fixed counterweight on a floating frame Pros: Wheels More vertical fall Easy to move and adjust Cons: Counterweight may be difficult to attach The floating arm trebuchet most accurate Vertical counterweight Difficult to build

Planning Process Choosing the arm: We chose the swinging counterweight trebuchet because it was the easiest for us to build with limited resources. Easily adjustable for distance by adding or removing weight. The vertical counterweight fall adds more power to the trebuchet we built.

Guiding Questions How big will the base be? These questions were to illustrate the many number of choices we were faced with on this project. A different answer could have completely changed the outcome. How big will the base be? How will we attach the wood together? What will we use as a counterweight? What type of axel will we use? What will the sling be made of?

Roles ALEX: Designing (drawings), Arm (cutting, sanding, construction) , sling, track construction CHLOE: base construction (cutting, gluing, stapling, sanding) track support (cutting, sanding, gluing, stapling) Throughout the trebuchet process we would consult each other for opinions or assistance.

Materials Given Wood Nails Eyehooks Metal rod Ready rod Bolts Washers String Twine Glue Fabric

We drew out the rough design to scale and recorded the measurements. Designing We drew out the rough design to scale and recorded the measurements. (Unfortunately we didn’t see that the base was too wide and too short.)

Creation Measurements and rough sketch Planning the cuts Building and Sanding the pieces

The Final Product

Goal To have the trebuchet fire a tennis ball 25 feet into a plastic recycling bucket.

Testing Attempt #1: Attempt #2 Attempt #3 Attempt #4 10 lbs. of weight. Traveled roughly 3 feet. Ball went higher up than further. This may have been because of the weights hitting the track when going downward. So, we decided to shorten the loop attaching the weight to the arm. Attempt #2 Traveled roughly 4 feet. The ball went slightly further. In an attempt to make it travel even further, we added 1.5 lbs. of weight and shortened the sling length. Attempt #3 Travel about 6 feet. The ball went quite a bit further but still nowhere near the box. We decided to change the twine attaching the sling to a thin green string hoping it would change the tension. Attempt #4 Traveled around 8 feet. We used a ten pound weight, and loosened the sling loop. We also slightly adjusted the sling rod. It was our most successful trial, and it traveled more than twice the distance of our first try.

Evaluation Unfortunately, our trebuchet didn’t complete our intended goal. This is probably because our base was too long, and so the angle between the supports was far too wide, thus shortening the base itself. With such a short base, we had to make our arm much shorter than we intended, so it would fit inside the base. Because of this, our throwing distance suffered, and we weren’t able to come close to our target. If we were to redo this project, we would pay closer attention to the measurements and see if they fit together, and also model the base measurements for optimal arm length.