How to Build a Catapult/Trebuchet

A trebuchet is a counterweight-powered siege engine from the Middle Ages. Medieval armies used trebuchets to hurl stones and other projectiles at enemy fortifications. They could vary in size, with the largest hurling massive boulders from far enough away to be safely out of the range of enemy archers. Although medieval trebuchets were powerful and dangerous machines, the principles used to build them were simple. It is not difficult to build your own miniature trebuchet, which you can use to throw fruit, tennis balls or balls of clay.

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Drawing materials
Wood
Saw or craft knife
Wood glue
Metal rod or pipe
Drill
Screw hooks
Screwdriver
Screws
Weights
Cord
Wire
Nails or pins
Cloth or leather
Scissors
Projectile

Instructions

- 1
  
  Choose a scale for your trebuchet. Medieval trebuchets could be as much as 50 feet high and capable of throwing a projectile more than a mile. A foot-tall trebuchet is much easier to make and can shoot up to 10 yards.
- 2
  
  Draw a plan for your trebuchet. You will need a swing arm, two pieces of wood to make up the base, two uprights, three cross pieces and two triangular supports to keep the uprights straight. The swing arm should be one-third longer than your base pieces and the uprights should be one-sixth shorter than the base. The cross pieces should be about half the length of the uprights. If you need some guidance on drawing the plan, consult an online plan, such as the design of the "Little Dragon" trebuchet on the Storm the Castle website (stormthecastle.com/trebuchet/how-to-build-a-trebuchet.htm).
- 3
  
  Cut the pieces of your trebuchet out of wood using a saw or craft knife.
- 4
  
  Place the base pieces flat on a work surface and attach one upright to each base piece at right angles. The upright should be about one-quarter of the length of the base piece back from its forward edge. You can attach these with wood glue if your model is small. If it is larger, you may want to cut a slot in the base piece to fit the end of the upright into.
- 5
  
  Attach the triangular supports to the side of the uprights and base pieces to give them rigidity.
- 6
  
  Attach the cross pieces to the base pieces, one at either end and one between the uprights. You can also add a flat piece of wood or plastic over the top of the cross pieces to create a smooth surface.
- 7
  
  Choose a length of metal pipe or rod to be your axle. It should be slightly longer than the distance between your uprights.
- 8
  
  Drill a hole through the throwing arm to receive the axle. The hole should be one-quarter of the way down the length of the throwing arm. Drill two more holes, one on either side of the first. The distance between the holes should be 1/16 of the length of the arm.
- 9
  
  Drill corresponding holes near the tops of the two uprights, making sure that the axle will fit through them. Push the axle through the hole in one upright, through the hole in the throwing arm, and then through the hole in the opposite upright. Test the swing of the throwing arm to see that it has room to swing freely.
- 10
  
  Insert a screw hook into the end of the throwing arm nearest to the axle.
- 11
  
  Select a heavy object to use as a counterweight. Medieval trebuchets often used rocks or large buckets filled with earth. Use wire or cord to attach the counterweight to the hook in the end of the throwing arm.
- 12
  
  Bend a nail or pin so that it has a slight angle about halfway along its length and push it into the head of the throwing arm at the opposite end from the screw hook. Insert another screw hook into the underside of the arm near the head.
- 13
  
  Cut cloth or leather to make a sling pouch. Attach a short length of cord at either end and tie one securely to the screw hook near the head end of the throwing arm. Make a loop from wire and attach it to the other end, slipping the loop over the bent nail or pin.
- 14
  
  Place your projectile in the pouch. Depress the head end of the throwing arm, which will raise the counterweight. When you let go, the counterweight will fall, swinging the arm around and releasing the projectile. You will have to experiment to find the correct angle for the nail and length of the pouch in order to get the best release.

Tips & Warnings

The multiple holes in the throwing arm allow you to adjust its length. See what effect a different length arm has on your shooting.
Always use caution when working with saws or craft knives.
Do not shoot your trebuchet at people or fragile objects.