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).

Although modified for the class requirements, this is not an original design. It was reversed engineered from a combination of the versions you will see online.

See video for actual build.

Materials:

• 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

Tools:

• Saw
• Drill
• Ruler

Notes:

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.

Cut PVC pipe to the lengths shown in materials list

Assembly the lower frames assemblies

Connect assemblies together with 30” pipe

Add the 17” pipes off the 45 degree fittings

Attach the upper frame assemblies to the upper sides of the pipe

Feed the 4” pipe through the launching arm between the two upper frame assemblies

Tie the 5lb weight to the launcher arm

Cut a piece of wood 30” x 4.75”. Thickness doesn't matter (.25” to .75” will work). Find or print out a ruler and attach it to the wood. This version was printed and covered with clear packing tape.

Drill a hole in the ¾” end caps. Pre-bend a pin (nail) to a 60 degree angle. Place pin in the hole and use epoxy to secure the pin to the cap.

As mentioned above, the arm length can be adjusted by swapping out the launcher end caps (short, medium and long). Make sure pin is facing forward.

Cut a piece of fishing line to 26” long. Tie knots on one side of the line. Drill or poke a small hole through the diameter of the squishy ball (slightly bigger than the fishing line). Feed the straight end of the fishing line through the ball. Tie a 1” diameter loop on the other end of the line.

Cock trebuchet by pulling the ball back along the board. Record the cocking distance on the data sheet. The ball should fly up to 50 feet.

Attached are the Drawing and Data Sheet