Video of me shooting the catapult:
(Sorry the video is sideways, I was having technical difficulties)
Step 1: Materials
Cardboard! - You will need A LOT of cardboard for this project unless you are lucky like me and find some quadruple-layer cardboard lying around.
Glue - I used Gorilla Glue and suggest that you use the same.
(Optional) Clamps - If you are using Gorilla Glue, you will most likely need clamps to keep your pieces together while the glue cures.
Pipes/Rods - You are going to need pipes for the axles and joints. I used a 3/4 inch acrylic rod for the axles and 3/4 inch PVC pipe for the axle to slide through.
Washers - You will use these to reinforce the joints that will be holding the counterweight and the the "arm" of the catapult. I used washers with a 7/8 inch hole.
Drill+Drill Bits - Depending on the size of your axle, you will need corresponding Drill Bits to make your holes. I used 13/16 inch and 5/8 inch.
Newspaper - Newspaper works really well when you are making your patterns for the cardboard
Rope/Cord - This will be for the "sling" that throws the projectile
Denim/Canvas Fabric - Also for the "sling"
3/16 Inch Steel Rod - This is also for the sling and only needs to be about 6 inches long
You will also need something to cut your cardboard into shape. I used a scroll saw but a knife or other saw might work.
Step 2: Trebuchet Design
Part A - This is the counterweight and consists of two different pieces, pieces A1 and A2. The more A2 pieces you have, the wider your counterweight is and therefore the more weight you can put in.
Part B - This is the "arm" of the catapult and has two joints, one where it meets the counterweight, and one where it meets Part C
Part C - Raises the throwing mechanism off the ground. Has one joint where it meets Part B. If this part is too short, the counterweight will hit the ground instead of sliding smoothly through the movement
Part D - Provides stability and keeps the trebuchet from knocking itself over. The longer it is, the more stable the trebuchet
Part E - Adds necessary strength to Part C
Step 3: Making Patterns
Part A1 -
20 in. wide - 20 in. tall
Part A2 -
20 in. wide - 11 in. tall
Part B -
41 in. long
4 in. wide at top / 6 in. wide at bottom
Part C -
41 in. long
6 in. wide at top / 8 in. wide at bottom
*Parts D and E will be covered in another step
Step 4: Cutting Out the Pieces
For Part A1, I used 8 layers of corrugation, four on one side and four on the other
For Part A2, I used 16 layers of corrugation
For Part B, I used 12 layers of corrugation
For Part C, I used 24 layers of corrugation, 12 for one side and 12 for the other.
Step 5: Gluing Parts A-C
If you don't have enough clamps, you can lay bricks or other heavy objects on top of the pieces while they dry.
Step 6: Drilling the Holes
Two of the holes need to be drilled on the "arm" of the Trebuchet (Part B). The first hole should be 2-3 inches away from the wider end. I used a 13/16 inch drill bit to make this hole. Using the same drill bit, drill another hole approximately 10 inches from the wider side. It'll take some force, and maybe a couple pounds from a hammer, but shove a piece of 3/4 inch PVC pipe into each of the holes. Pre-cut these pieces of PVC so that they are flush with the cardboard on either side. See first picture for clarity
Drill 5/8 inch holes 2-3 inches from the narrow end of Part C. See second picture for clarity.
Drill 5/8 inch holes into the top of the counterweight and glue the washers around the holes. See third and fourth picture for clarity.
Now cut your 3/4 inch axle into a six inch piece and a 15 inch piece. Take the six inch piece and slide it through one side of the counterweight, then through the "arm" of the trebuchet (in the hole closest to the edge), and through the other side of the counterweight. Take your 15 inch piece and slide it through Part C. Slide the rest of the rod through the other hole in the "arm" and then through the hole on the other half of Part C. See fifth picture for clarity.
Step 7: Parts D+E
Glue these piece to the bottom of Part C as shown on the second picture.
Part E are by far the most important supports. I tried firing the trebuchet without Part E and it had so much power that it ripped off all of the supports I had just put on in Part D.
Cut out pieces that are 4 inches wide and 27 inches long. You will need four pieces that have 12 layers each. Glue these pieces together. Trace the exact angles you will need on both the ends onto each of your pieces. Cut the pieces to shape and glue them in place. See pictures for clarity.
Step 8: Making and Adding the Sling
Depending on how big the items are that you will be throwing, your denim pouch will vary in size. My pouch was about 8 inches by 10 inches.
Take the edge of the side that is eight inches long and fold over about half of an inch. Sow this flap over and do the same on the opposite side. Slide your rope/cord through these folds. both these strings should be the same length. Take one of the strings (after you have fed it through) and tie it so that it makes one big loop. Leave the other string untied. See picture for clarity.
Drill a hole in the "arm" of the catapult on the side opposite of the counterweight. This hole should be just big enough for you rope/cord to fit through.
Take the untied rope/cord and feed it through this hole. Once it is run all the way through the hole, tie it to the other end of the rope/cord.
Take your six inch rod and poke it into the cardboard near the hole you just drilled.
Step 9: Firing and Adjusting the Trebuchet
Firing the Trebuchet
Adjusting the Trebuchet
For more power, add more weight to the counterweight. Here are some ideas for filling your counterweight:
- Bricks work well, but only if they fit width-wise
- thick gravel will work sometimes, but sand will seep through the corrugation
I ,however, used a 20 pound shirt of maille armor that I made last year. It fits perfectly and does not shift during the firing sequence.