Generating Ideas:

Our group (James and Kyle) have decided to make a wooden trebuchet as a project for our G9 engineering project. The wooden trebuchet involves energy transfer; for instance, it utilizes gravitational potential energy and turns it into kinetic energy when it is functioning. The trebuchet’s primary material will be wood, except for the weight; it will probably be made of metal since it’s heavier than other materials.

Additional Research:

This video explains the procedure of making a trebuchet. They made the basic structure of the trebuchet first, and then they added the arm and the weight as well as the basket where you can put a tennis ball inside. They uses wood as their main material except for the weights and wheels.

Sketch:

This will be the basic model of the trebuchet that we are going to make.

Materials:

Wood

Metal (Weight)

Procedure/Steps (Plan):

Step 1: Cut the wood

Cut the two-by-threes, two-by-twos, and one-by-threes to length using the displayed cutting guide. If you have a power saw, you can use that instead of the hand saw and miter box we used. Take note that some of the two-by-twos need to have 45-degree cuts. Two 28″ pieces of the wedge casing and an 8″ piece of 7/8″ dowel must also be cut.

Step 2: Frame-marking

Draw a line across the board 11″ from one end of two of the 28″ two-by-threes. This will serve as a guide for mounting additional trebuchet frame components.

Step 3: Drill pivot arm holes

To prevent drilling through your work surface, stack the 15″ two-by-threes and clamp them on top of a scrap piece of wood. One inch in from the top two-by-end, three’s mark the center, then use a 7/8″ spade bit to drill a hole through both pieces of wood. You can also use a pencil to mark the location of the hole, as we did. The trebuchet’s arm will pivot around this.

Step 4: Drill axle-related holes

On the same side as the 6″ pieces, mark the 28″ two-by-threes 2 1/4″ in from each end. Drill four 3/8″ diameter holes, one on each end of the two-by-threes, while clamping it to a scrap piece of wood. This will serve as the wheel axle holes.

Step 5: Attach the trebuchet sides.
We will now attach the sides of the trebuchet together using two 5″ two-by-threes. Place one 5″ two-by-three at each end of the 28″ pieces, standing on their sides and fitting nicely between the 28″ pieces, with the 6″ pieces facing outward and the 15″ pieces upright. To secure, insert a 2 1/2″ screw through each end.

Step 6: Install the bracing

Trebuchets must be constructed to withstand the laws of physics since they employ motion and counterweights. Braces can help in this situation. Place the two 18″ two-by-twos with angle cuts on the long side of the frame so the ends connect to the 15″ upright beam and the base of the trebuchet. Use 2 1/2″ screws to secure. On the opposite end of the frame, attach the 14″ two-by-twos in the same way. Determine the correct angle before creating the trebuchet’s side braces. Hold an about 12-inch-long two-by-two against the frame. Put one end on the edge of the upright and tuck the other under the top of the 18″ brace. The opposing end will sit next to the 6″ two-by-three. After penciling in each angle, use a hand saw to cut it out. You can clip a speed square to the board to act as an easy guide for the saw if you want to make a straight cut without a miter box. Use 2 1/2″ screws to secure the side brace. For the other side, repeat.

Step 7: Making the trebuchet track

To make a track for the projectile, position two 28″ lengths of wedge molding on the trebuchet base so that they slope together. Drill beforehand and use 1 1/4″ screws to anchor.

Step 8: Get the pivot arm ready and attach it to the trebuchet

Drill a 3/8″ hole by centering your drill bit, measuring 1 1/4″ from the end of the remaining 28″ two-by-three, and drilling. Later, the counterweights will be mounted here. Drill a 7/8″ hole for the pivot arm’s axle 6″ in from the same end next. Slide the 8″ length of dowel through one upright, the pivot arm, and then the other upright while holding the pivot arm between the two uprights. Pre-drill holes in the uprights, then use tiny screws to fix the dowel in place. Drill two 3/16″ holes in the dowel on either side of the pivot arm and slide two 3/16″ dowel pieces into the holes to secure the pivot arm. The dowel could be replaced by small screws.

Step 9: Attaching the weight plus the hardware and make the basket

Attach the weight on the end of the arm, and attach the basket on the other end of the arm. Drill the hardware at the base of the trebuchet. It going to hold the arm while the trebuchet is not functioning.

Schedule:

February 21st: Figure out the scale of the trebuchet, make the frame, and the supporting structure, combine the trebuchet sides and attach bracings.

February 23rd: Prepare the pivot arm, and drill the holes for the dowel that goes through the frames and the arm of the trebuchet.

February 27th: Mount the trebuchet track, attach the weight, and cut out the basic shape of the basket.

March 1st: Attach the sling to the trebuchet, add the release mechanism, and finally test it out.

Success Criteria:

1. Developed a prototype that can shoot a ping-pong ball using knowledge of the physics of a golf swing.
2. Be sure to demonstrate an energy transfer of some kind (Gravitational potential energy –> Kinetic energy).
3. Complete the prototype before the due date.

Works Cited:

Dunn Lumber, Building Success Together. “How to Build a DIY Mini Trebuchet”. Dunn Lumber, 14 Jul 2020, https://diy.dunnlumber.com/projects/how-to-build-a-diy-mini-trebuchet. Accessed 17 February 2023