Trebuchet Hybrid Launching Device

Introduction: Trebuchet Hybrid Launching Device

A trebuchet is a version of a catapult that used gravity to launch a projectile in the air. I achieved this using a small arm with a counterweight that comes down to launch a tennis ball (or whatever payload you want) with a sling. To make our trebuchet more accurate we decided to replace the sling with a cup and have a leash mechanism to stop the arm at 45 degrees. Our goal is to launch a tennis ball 10, 20 and 30 yards into a 34 by 34 inch hoop.

Step 1: Materials

  1. 3— 2” x 4” x 8’
  2. 15 ft of rope-¼” Braided Polypropylene Rope
  3. 2 eye screws
  4. 9 oz. Plastic cup
  5. Wooden dowel 1 inch diameter
  6. 1— ½” x 10’ PVC Pipe
  7. 20 Wood screw
  8. 9 Washers
  9. WD40
  10. Miter saw
  11. Mallet
  12. Drill
  13. Driver
  14. Safety glasses
  15. Work gloves
  16. Ear plugs

Step 2: Base

  1. Gather two 2 by 4’s( 2” x 4” x 8’) and 8 wooden screws.
  2. Start by cutting one of the 2 by 4’s( 2” x 4” x 8’) in half; cut it vertically in half while laying on its longest side. You will end up with TWO 2” x 4” x 4’ (as seen in the example). Put the two pieces to the side for later.
  3. Take the other 2 by 4( 2” x 4” x 8’). Measure out 3ft and 4 inches of the 2 by 4, and mark where the measurement ends. Cut at the mark and put the rest to the side. Take the 3ft and 4 inches and cut vertically in half. Once you cut it in half you will have TWO 1ft and 8 inch pieces.
  4. Take the two 2” x 4” x 4’ pieces(from step 2) and the two 1ft and 8 inch pieces(from step 3). Align the pieces together making a rectangle. The two 2” x 4” x 4’ pieces are on opposite sides and the two 1ft and 8 inch pieces are on the opposite sides.
  5. Drill TWO holes at the end of each corner( drill the holes long enough for the wooden screws to fit). The hole needs to go through both pieces of wood and needs to be at least 1cm away from the end of the wood.Take the wooden screw(s) and drill them in.

Step 3: Arm Part 1

  1. Start by gathering a (1) 2 by 4, the one that cut 2 feet off
  2. At 1.26-1.27 ft drill 1 in hole in the middle of the arm. This will separate the short arm from the long arm and will also be our pivot point. For a quick test take the wooden dowel to see if it fits through the hole, if not use a file to file the hole where it slides in without the hole being too big.
  3. 3 inches from the end of the small arm drill another 1in hole in the middle of the arm.

Step 4: Y-frame

  1. Cut the 10 foot PVC pipe into 4 pvc pipes that are 2.1 ft long using the miter saw
  2. Cut out two 4ft tall planks that are 3.5 in by 1.5 in. and cut a 0.7 inch hole
  3. Place the 4ft ones on either side of the base.Then connect
  4. Angle the 4 pvc pipes from before as a 45 degree angle 1 on each side of the 4ft high planks
  5. Washers will be needed for wooden screws to attach to the main wood plank. 2 washers and 2 screws per pvc pipe
  6. Bend the washers with a mallet so it will fit perfectly on our pvc pipe

Step 5: Arm Part 2

  1. Now you have your short arm and your lang arm. Check to make sure that the short arm has a measurement of roughly 1.26ft from the 1 in hole (the first you drilled). Check that the long arm (the wood behind the first hole you drilled) is 4.75 ft long.
  2. String the 6ft of rope through the second hole.
  3. Using the Quick link attach the 50lbs of weight plates to the paracord making sure to wrap it and knot it well.
  4. Now that the short arm is finished gather the plastic cup, a washer, and a wood screw.
  5. Now you will be working on the 1 ½ part so first place your plastic cup at the edge of the long arm so that the edge of the cup is touching the edge of the wood.
  6. At the base of the inside of the cup in the middle place a washer
  7. Then using the drill create a pilot hole through the cup and wood
  8. Finally screw in a wood screw to secure the cup
  9. On the opposite side (underneath the wood) of the cup attach the eye screw(For this step you should not need to drill a pilot hole)
  10. Drill a small pilot hole in the small half piece of wood closest to the long arm (this is on the base)
  11. In the hole from step 10 place another eye screw

  12. Cut the wooden dowel so that it is 3 feet long

  13. Oil down the dowel with WD40.
  14. Start to thread a dowel through the 0.7 inch hole in the y-frame, (not all the way as shown below) if needed mallet it in being careful of not breaking it.
  15. Once the dowel is threaded through one of the hole in the y-frame bit insert the arm through the dowel using the first hole you drilled.

  16. Now push the dowel through the next y-frame hole (use mallet as needed)

  17. Where the dowel meets the y-frame screw a wood screw after you drill a pilot hole.

  18. Using the last 8 feet of rope and tie one end to each of the eye screw
    (We want 8 feet so that it can be easily adjustable to your needs)

Step 6: Testing and Adjustments


Some adjustments made to this design:

The Y-frame will be screwed and attached to the sides of the trebuchet for more support. The the pvc pipe was changed out for wood.

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