Plastic Teamwork Trebuchet Documentation Page

Human Powered Trebuchet

In Medieval times, the trebuchet was one of the largest and most expensive siege machines on earth. With giant wooden throwing arms and counterweights weighing many tons, the trebuchet was used to hurl heavy boulders and break down castle walls, or fling dead animals or other disease carriers over walls at safe distances.

No heavy counter weights here, though. Instead, this project is an inexpensive, portable, human-powered machine that can toss water balloons farther than you ever imagined by hand with relative consistency. It’s a modern take on a very old idea, requiring team work and cooperation.

This documentation is based on a design supplied by John Park found at Makezine.tv

I have a page on an alternate version that was made out of wood. Please visit it here - Wooden Teamwork Trebuchet Documentation Page

This has basically been changed to become an original design implemented by the Adults and Cub Scouts of Pack 40 (Costa Mesa, CA) and Pack 22 (Santa Ana, CA). Safety features appropriate for cub scouts have been added for water balloon throwing fun.

We commonly like to call this the Teamwork Trebuchet since it takes two people to operate effectively.

This design has been approved and used by Congresswoman Loretta Sanchez (D-CA).

Look for or new and improved design made of wood instead of Plastic piping in the near future.

Materials

Note: All pipes and fittings are schedule 40 ABS or PVC, 1½” in diameter. PVC is usually white. ABS is typically black. We will use the cheapest; either will work.

10’ long pipe (6)

End cap fittings (7) (5 if you decide to skip step 6)

Threaded pipe unions (4)

Pipe coupling (4)

90° elbow fittings (6) (4 if you decide to skip step 6)

Tee fittings (2)

Adjustable tee fitting (Used for counter weight arm – get three way adjustable if possible)

Sturdy plastic dish with flat bottom

½” diameter, fully threaded bolt or threaded rod, 8” long

5 nuts for ½” diameter bolt (this can be reduced to 2 is using hosing)

2 1” sections of hosing for ½” diameter bolt

6 washers for ½” diameter bolt

3/8” diameter bolt, 5” long, washers and nuts (5 – 1 nut and 2 washers each)

Cement appropriate for the type of plastic used

Sandbag (2) and/or tent stakes (2)

Tools

Electric drill

½” drill bit

3/8” drill bit

Saw

Miter box

4” or larger C-clamps (3-4)

Scrap wood

File or dermal tool

Estimated Cost: Under $100

Project Overview:

The photo below shows the main sections of the trebuchet:

v Throwing arm

v Throwing arm supports

v Base

v Upright assembly

Step 1: Cut the pipes to length

Plastic plumbing pipe typically comes in 10’-long pieces. Using a

miter box to maintain straight cuts, cut the following lengths of pipe:

v 5’ long pipe (6)

v 80” long pipe

v 4’ long pipe (2) (You may decide this needs to be longer)

v 8” long pipe (2)

v 3” long pipe (4)

v 3’ long pipe (Approximate. Will be cut to size in Step 3.)

Step 2: Build the base

Lay out two 5’ pipes, two elbows, two 3” pipes, two unions, two 8” pipes, and two tees, as shown in the photo below.

Assemble all the pieces to make sure everything fits. Disassemble. Cement the pieces together, one junction at a time.

The process of joining and cementing plastic pipe is technically called “solvent welding.” The solvent melts the plastic so when you push the two parts together they fuse as the solvent evaporates. Make sure to acquire the right kind of cement for the type of piping you are using. Using the wrong type will destroy the pipe and not cause proper fusion.

Make sure to follow the instructions carefully on the cement you picked out in regards to using primer or not. Then apply the cement and push the pieces together. The cement should set quickly, leaving a strong and permanent bond.

WARNING: Make sure to apply the cement in a well ventilated location or outside. Solvent welding can create lots of fumes which are potentially toxic.

Step 3: Build the upright assembly

Lay out two 5’ pipes, two elbows, two 3” pipes, two unions. Dry fit pieces together, and then lay the uprights next to the sides of the base. Measure the distance between the unions on the upright assembly. Cut the pipe to length so that the pipe is well seated between the unions. (Our length was ~30”.) Disassemble, then carefully apply cement and fit pieces together to form the upright.

Step 4: Attach the upright assembly to the base

Measure and mark a point twelve inches from the end of the base. Then, measure and mark a point two inches from the end of the upright assembly. Clamp the upright assembly to the base using the C-clamps. Drill a 3/8” hole through both sides. Insert a 3/8” bolt, with a washer on each side of the plastic pipe and secure with a nut. Repeat this process for the other side of the trebuchet.

Step 5: Complete the triangle

Cement the two remaining 5’ pipes into the tees on the base. These pipes will form the throwing arm supports. Then, raise the upright assembly up to the throwing arm supports so it forms a triangle with the base when seen from the side.

Next, clamp the structure with C-clamps and wood scraps as shown in the picture. The throwing arm supports should extend 12” beyond the crosspiece of the upright assembly. Using a 7/16” drill, drill a hole through the clamped upright assembly and each throwing arm support. Insert a 3/8” bolt, with a washer on each side of the plastic pipe and secure with a nut.

Step 6: Rear stabilization section (This step is optional)

The rear of the base tends to want to bow inward. To correct this issue you will want to add two (2) elbows and a piece of pipe to the rear. This assembly will be dry fit to the rest of the trebuchet. You will need to cut the piece of pipe to length much like you did with the piece on the uprights. Measure the distance between the legs of the base. <<See Picture>>. You will need to cement the elbows to this piece. Do not cement this piece to anything else or you will not be able to disassemble for transport.

Step 7: Reinforce throwing arm

The 80” length of pipe will function as a throwing arm. The throwing arm will also attach to the trebuchet structure with a ½” bolt, but drilling through the pipe will weaken the throwing arm. Reinforce the throwing arm by placing a pipe coupling over the throwing arm at the point where the hole will be drilled. To be able to fit a pipe coupling around the throwing arm, you’ll have to remove the ridge from the interior of a pipe coupling using a rotary grinding tool or file.

Measure and mark a point 20” from one end of the throwing arm. Slide the coupling down the throwing arm until it is centered on the marked point. Drill a ½” hole through the pipe coupling and throwing arm.

Step 8: Attach the throwing arm

First, drill the holes in the throwing arm supports. Measure a point three (3) inches down from the top of each throwing arm support. Taking care to keep the drill level, drill a 1/2” hole through both supports.

Using the ½” threaded rod or eyebolt, attach the throwing arm to the trebuchet as shown in the picture below. You will use two nuts as spacers on each side to keep the arm centered in the space between the two throwing arm supports.

When using a fully threaded bolt you may find you need to use a double nut assembly to properly position the bolt. The nuts will lock against each other causing the necessary movement. This also is where you find you may strain your pipe. It would be advisable to use two pieces of hose instead for spacing.

Step 9: Attach launcher bucket

Drill a 3/8” hole towards the long end of the throwing arm. Drill a corresponding 3/8” hole in the middle of the bucket. Insert a 2 ½” 3/8” diameter bolt with a washer on each side of the plastic pipe and bucket then secure with a nut.

Make sure to tag the extended piece of bolt that hangs out the bottom. You may want to instead cut off the excess for safety reasons if tagging it does not work.

Step 10: Reinforce upright supports and cross beam

Banging the upright supports with our human powered counter weight cross beam pipe will weaken the upright supports. Reinforce the upright supports by placing a pair of pipe couplings over the upright supports at the point where the pipe will hit. NO need to reinforce the throwing arm supports you will not be hitting them during motion. You do not need to do the same to the counter weight cross beam (this is from the T-jointed pieces at end of throwing arm). To be able to fit a pipe coupling around the upright supports, you’ll have to remove the ridge from the interior of a pipe coupling using a rotary grinding tool or file as we previously did for the throwing arm. Then you’ll want to split the couplings in half.

Measure and mark a point on the upright supports (you may need to eye ball the hit location). Make sure to cement these down so they stay secure.

Do the same with a split coupling in the small section between the throwing arm supports on the cross bar. Due to the somewhat flexible nature of the pipping and couplers you may find thing shift a bit. It does not hurt to put extra coupler supports on the upright supports.

You’ll may want to put additional foam padding over the impact points on the uprights.

This will help lessen the strain from over zealous users.

Step 11: Attach human powered counter weight cross beam

Attach an adjustable tee joint on the long end of the throwing arm. Make sure to cement down this piece. It will be able to detach due to the threaded portion. Attach a 4’ piece to each end of the tee joint. Make sure to cement these pieces in. There should not be a lot of play in this piece if you firmly attached all parts. Due to length you may find the ends to wobble a little in relation to the throwing arm. If you have been able to acquire a 3 way adjustable t-joint you can make spare arms that are easy to replace when a break occurs due to much force on arm.

Step 12: Apply end caps

Now you will need to put in place the end caps. These caps will be placed at the ends of the throwing arm supports, human powered counter weight cross beam, cup end of throwing arm, and if you decided to skip step 6 at the ends of the base.

WARNING:

1. Position your hand such that it does not get pinched against the throwing arm supports when you push down.
2. The trajectory of the projectile can be hard to predict, especially initially. Should the trebuchet “misfire” be aware that your projectile could land anywhere in front of or behind the trebuchet.
When in motion, the throwing arm is dangerous. Keep people (and pets) away from the moving arm.
Be careful when you are positioning the ½ bolt that attaches the throwing arm to the throwing arm supports. If you have used nuts and not hose as spacers you may stress the pipe when attaching the throwing arm. Over time this can cause a 'stress break' that ruins the arm and PVC pipe.

Your human powered trebuchet is now complete!

This trebuchet now will require two persons to launch.

Use the video at the following link as reference. Our launcher is based on this one. http://www.wonderhowto.com/how-to-build-huge-trebuchet-that-flings-water-balloons-272344/

I have a page on an alternate version that was made out of wood. Please visit it here - Wooden Teamwork Trebuchet Documentation Page

Trebuchet resources and documentation

Makezine video of Pipe Trebuchet construction

http://blog.makezine.com/archive/2009/02/maker_workshop_portable_trebuchet_o.html

PDFof building instructions

http://blog.makezine.com/archive/2009/02/maker_workshop_pdf_portable_trebuch.html

http://cdn.makezine.com/make/television/trebuchet.pdf

U of U Construction instructions

http://www.mech.utah.edu/events/trebuchet/trebuchet_construction.pdf

Video relating to Pipe Trebuchet

http://www.youtube.com/watch?v=0so62fr6jU4

Details PVC trebuchet instructions and parts list