How to Build a Trebuchet

A trebuchet is an engine that uses a swinging motion to break walls or launch objects over them. It is traditionally made of pieces of wood. It is similar to a catapult but is able to launch objects more accurately. The first versions needed men to apply force while later models simply used a counterweight.

 

Tools

 

  • hammer
  • metal cutters
  • saw
  • sandpaper
  • needle nose pliers
  • drill and bits
  • screwdriver
  • file
  • wood glue
  • scissors

 

Materials

 

  • 1 sheet of cardpaper (material similar to cereal box)
  • small screws
  • wood (1” in width and ” – ¼” in thickness)
  • wide wood planks
  • small nails
  • paint and/or varnish (optional)
  • 6″ x 6″ piece of cloth
  • 2 eyehooks
  • 3-ft string
  • wire or bread ties
  • electrical or masking tape
  • metal piece (radius depends on you, length should be longer than 5 inches, it should be strong enough to handle the weight from the counterweight and the swinging action)
  • any heavy object for the counterweight (you can use a stone, used batteries or pennies)
  • a ball for the projectile

1. Borrow or purchase any needed tools you currently do not have.

2. Cut the wood into the following pieces you need:

a) one (1) 16-inch piece for the swing arm

b) two (2) 12-inch pieces for the long base

c) two (2) 10-inch pieces for the uprights

d) three (3) 5-inch pieces for cross pieces to be used with the base

e) two (2) pieces of right triangles (The height and length is either 5 or 6 inches. The two pieces must be cut exactly the same. This can be done by cutting out a 5 x 5 or 6 x 6 square and cutting it from one top corner to the opposite bottom corner.)

3. Make the base of the trebuchet.

a) Place a 10-inch piece of wood perpendicular to a 12-inch piece. Make sure the 10-inch piece is placed 3 inches from the left end of the longer piece. Combine the two pieces together with glue. Glue the wooden triangles on top of the two so that the right angle of the triangle is placed above the L-shape made by the two perpendicular pieces.

b) Repeat the above process for the other side of the base. Instead of the left end, glue the 10-inch piece 3 inches from the right end of the 12-inch length of wood. Finish by laying the triangle over the L-shape made by the perpendicular pieces of wood then gluing it on.

c) Place the two pieces you made. Connect them using the 3 pieces of wood that are 5 inches long. Place the two pieces at each end. Place the third piece at the L-shape where the vertical pieces stand. This third piece should be at the very corner of the triangles. Fix the three pieces with glue, nails, or screws.

d) Drill a hole about one inch from the topmost end of the vertical support. The size of the hole depends on the metal bar you are going to use.

4. Make the swing arm.

a) Screw a hook loop into one end of the 16-inch piece of wood. The hook must be screwed at the center of the thick part.

b) Drill holes on the face of the wood near the top (where the hook loop is screwed into the thick part of the center). Place the first hole 1 inch from the top of the wood. Drill another hole 1 inch away from the first one. Drill a third hole an inch away from the second. The holes must be a little bit bigger than the metal bar so that it can move freely.

c) Screw another hook loop at the other end of the 16-inch piece. The hook must be on one side, at the thick part.

d) Insert a nail at an angle into the center topmost part of the wood, the opposite of where the other hoop hook is placed. Remove the head of the nail by either cutting or filing it off.

e) Place your metal bar through one of the vertical supports of the base. Run it.

5. Place the metal bar through one of the vertical supports of the base. Run it through one of the holes in the swing arm and then run it through to the other vertical support. Make sure the top of the arm faces the shorter end of the base. The other longer part of the arm must extend towards the longer length of the base. Make sure the arm can swing freely.

6. Make the counterweight.

a) Tape up the heavy object you will use.

b) Attach wire or twist ties to the weight and attach it to the loop hook.

7. Make the string and pouch.

a) Take two pieces of string that are at least 12 inches long.

b) Place the ball for the projectile in the middle of a piece of cloth.

c) Tie one piece of string to each of the ends of the cloth to make a sealed pouch.

d) Attach a ring to one end of the string.

e) Attach the pouch to the end of the arm with the nail and the loop hook at the side. Tie one end of the string to the loop hook. Slide the ring of the other string into the nail.

8. A runway is needed for the pouch to rest on under the trebuchet. You can make a runway out of posterboard or a folder by folding it to act as a cradle that fits exactly into the base.

9. Test if the trebuchet can fire.

a) Pull back the arm so that the weight is lifted.

b) Let the pouch and projectile rest on the cradle.

c) Release the arm.

d) If the trebuchet is working properly, the counterweight will fall down. The arm will then swing upward and release the projectile from the pouch.