Launch It: Small But Mighty Trebuchet!

Learn how to make a mini firing trebuchet in this project. Our public library https://www.librarypoint.org/ has an ongoing competition called "Launch It!" where the community is invited to make smallish trebuchets and then launch them together in competitions based on distance, accuracy and decorative style! What is a trebuchet? Take a look here at all the differences between catapults and trebuchets. The key difference is that trebuchets use weight rather than tension to launch their payloads. It also makes for a great project that combines physics with woodworking, design and creativity. We will be building a working trebuchet using about $10 worth of materials here to get ready for our "Launch It!" competition. Our library has added a new category for younger makers. This small version is an addition to the middle-sized project you can find here: https://www.instructables.com/Launch-It-How-to-Trebuchet/ It is meant to be more simple and user-friendly than the more open-ended middle-sized project.

Teachers in the Fredericksburg area can contact me at sekingernc@staffordschools.net for support with laser cutting.

3 sheets of 12x12x1/8 plywood for laser cutting

Access to a laser cutter

1/2 inch x 4 ft dowel (3 dowels, each 7 inches long, 1 dowel 3 inches long)

saw

wood glue, super glue

clamps

rope

fabric/felt

1 trim nail

2 2 and 1/2 lb round weights

These laser cut files were designed to follow the guidelines of the "Launch It" small category and with the scientific principles of the included documentation. A finished trebuchet should be about 12x12x6 inches. Access the two .svg files to start building your trebuchet. You will need 3 pieces of plywood in total; I used 12 inch x 12 inch x 1/8 inch. You will need to cut out all parts, which was not a problem for a 10-watt laser. Cut 1 sheet of "parts" and 2 sheets of "sides".

Arrange all laser-cut parts. You will need:

4 sides

6 cross beams (notched)

3 arms

10 large discs

18 small discs

Use wood glue and clamps to begin to assemble. Start with the 3 arm pieces.

Assemble the trebuchet arm. It is a large rectangular part with three holes in it. Use wood glue to sandwich all three layer together and clamp tightly. Wipe all excess glue from the edges and inside holes. Be sure all holes align.

Gather the 6 crossbeams needed. Glue them into 3 pairs, each two pieces of wood thick. Clamp and let dry.

Gather 8 of the 10 large discs needed. Glue 8 of the discs in pairs of 2. You will use these for the 4 wheels of the trebuchet. Clamp all wheels as they dry. Reserve the final 2 discs for later.

Gather the 4 trebuchet sides. Glue them into pairs of two. Be sure that they are aligned so that each pair faces the same direction. Clamp and let dry.

Gather 12 small discs. Add small discs to dry trebuchet sides. Glue one small disc to each hole in the trebuchet side. There should be 3 discs on each side of the trebuchet. Continue to use wood glue or switch to super glue to speed up the process. *Note: be sure to wipe the inside of the holes before glue dries. Allow both trebuchet sides to dry.

Gather your three sets of glued crossbeams. Add more glue to the notch and attach these crossbeams to the bottom of the trebuchet. Be sure that the model is aligned as the glue dries.

Gather 2 7 inch dowels, 4 small discs and 4 glued wheels. Slide each dowel through the holes in the sides of trebuchet. Add 1 wheel to each side of the dowel. Do not glue these wheels. Add one small disc snuggly to each end of the dowels and glue in place. Use superglue to reinforce these. Check that wheels spin freely once glue is dry.

Gather 1 7 inch dowel and 2 small discs. Gather the trebuchet arm. Slide the dowel through the top pivot hole of the trebuchet side. Add one small disc, then the trebuchet arm, then the final small disc to the dowel. When adding the trebuchet arm, use the middle hole (one side of the trebuchet arm is longer than the other). Center the dowel in between the two trebuchet sides. Center the small disc, arm and other small disc on the dowel, Glue the small discs in place. Do not glue the trebuchet arm to the dowel. Check that arm swings freely once the glue is dry. Congratulations, the frame is done!

Gather some cord and a piece of fabric or felt. You will need to create a loop of cord that is as long as the length of the trebuchet arm. Cut a piece of cord 26 inches long and knot it in a loop through the hole in the long side of the trebuchet arm. Once the cord is knotted to make a loop, mark the middle of the loop by folding the cord in half. This middle part is where the fabric pouch will be placed. Cut a fabric/felt square about 3 x 2 inches. Tape, glue or stitch this fabric across the loop of cord to make a pouch that will hold your payload.

Use one trim nail to create the launch pin for the trebuchet. Nail it into the end of the trebuchet arm where you have attached the loop of cord.

Gather the small 3 inch dowel and 2 large discs. Slide the dowel through the hole at the short end of the trebuchet arm. Add the two weights and then a disc on each end. Glue the weights and discs in place so that nothing moves when the trebuchet arm swings.

Time to test the trebuchet! Gather something to launch, like a marble or bouncy ball. Start with something soft or light if possible. Please note that a trebuchet can fire its payload in nearly any directly, so be aware of your surrounding. Use two hands to prepare your trebuchet. With one hand, pinch the payload in its pouch so that it is centered and even. With your other hand push down on your swing arm until it is as low as it will go. Follow this motion with your other hand still pinching the payload and pouch. Place your body and arms on the side of the trebuchet and toward the back, out of the swing arm's path! When you are ready to launch, release the swing arm and let the pouch slide through your other hand. Be sure to keep your face and hands out of the reach of the swing arm and launch pin. Do keep some weight on the rear end of the trebuchet as it launches, so that it doesn't tip over.

Note: with the wheels in motion, the trebuchet should make a quick motion forward then back as it launches. This will improve the launch and keep the trebuchet from tipping over! See https://www.instructables.com/Launch-It-How-to-Trebuchet/ for troubleshooting suggestions.