Picture of Trebuchet Project

This project is currently being used for a middle school intro to engineering program. This project is pretty simple to build and just about any home improvement store will have the supplies.

The kids are given the materials and the trebuchet drawing (see link in description). It takes the average group (2 to 5 kids) about 10 minutes to assembly the trebuchet. There are two variables in the setup. The first is the launching arm – three choices are available: short, medium and long. The other variable is the height of the weight. This is controlled by the distance on the ruler attached on the board at the base of the trebuchet. Data is collected for the three arm lengths across the weight height range (see link to spreadsheet). After the data is collected, a competition is held to hit a target (bucket, 20 feet away).

See video for actual build.

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Step 1: Materials, Tools and Notes

Picture of Materials, Tools and Notes


  • PVC Pipe, 1/2” diameter x 30” Long (x2)
  • PVC Pipe, 1/2” diameter x 17” Long (x4)
  • PVC Pipe, 1/2” diameter x 4” Long (x3)
  • PVC Pipe, 1/2” diameter x 3” Long (x4)
  • PVC Pipe, 1/2” diameter x 1.5” Long (x12)
  • PVC Pipe, 3/4” diameter x 17” Long
  • PVC Pipe, 3/4” diameter x 8” Long
  • PVC Pipe, 3/4” diameter x 6” Long
  • PVC Pipe, 3/4” diameter x 4.5” Long
  • PVC Pipe, 3/4” diameter x 1.5” Long
  • PVC Elbow, 1/2”, 45 degree, Female Unthreaded Socket Ends (x8)
  • PVC Tee, 1/2”, Female Unthreaded Socket Ends (x10)
  • PVC Tee, 3/4”, Female Unthreaded Socket Ends
  • PVC Cross, 3/4”, Female Unthreaded Socket Ends
  • PVC Adapter, 3/4”, Unthreaded & Female thread
  • PVC Adapter, 3/4”, Unthreaded & Male thread (x3)
  • PVC Cap, 1/2”, Female Unthreaded Socket End (x4)
  • PVC Cap, 3/4”, Female Unthreaded Socket End (x3)
  • PVC Glue/Cement
  • Pin or nail – 1/8” diameter x ¾” long
  • Epoxy
  • Wood – 30” x 4.75” x 5/8”
  • Paper Ruler – 30” long
  • Clear Packing Tape
  • 5lb weight
  • Rope (30”)
  • Rubber squishy ball
  • Fishing line - 26” long


  • Saw
  • Drill
  • Ruler


Refer to the drawing for build instructions (last step). Note that Upper and Lower frame joints (items 1 and 2) are shown as assemblies on the drawing. This is an optional step which was done to speed up the build process for classes that had limited time. Both of these assemblies were glued together. The launching arm assembly must be glued together to support the weight and swinging motion.

ShiftP2 days ago

If i double the diameter alone of the pvc in all portions will it work? If so if i double the length of the pvc and keep the diameter the same will it work? And if i double both the diameter and the length of the pvc beefing the scale up by 100% will it work? With the first 2 questions, will either of the changes if they work will it effect the distance the projectile will travel?

mtairymd (author)  ShiftP2 days ago

1st question: Yes, it will work. Not needed though - 1/2" diameter is strong enough.

2nd question: It would most likely fail due to the longer runs of 1/2" pipe (not strong enough)

3rd question: I think it would work fine if you scaled both. I would actually like to see a scaled up version with 1.5" pipe. Maybe you could launch a soccer ball or something.

4th question: I don't think the first option would help much - might even slow it down. The second option would probably break.

bricobart8 months ago

I was waiting for the first trebuchet in the contest, nice work ;) To add more stiffness to the launching pole you can glue a smaller pipe inside, or a wooden pole. What about the range? Tested?

Adding more mass to the pole reduces the transfer of momentum to the item being tossed due to the increase of inertia. It is best if the parts of the trebuchet all have the lowest mass possible except for the weight, especially as they are get farther from the pivot.

mtairymd (author)  bricobart8 months ago

Thank you. We don't seem to have much bending in the launching arm. As for range, it sends the ball about 45 feet. As part of the project, we roll out a 50 foot ruler on the ground. See excel spreadsheet for test data.

mgreen207 months ago
If u put it on wheels u could get up to 20% more power
mlay28 months ago


mlay28 months ago