Human Powered Trebuchet
(Teamwork Trebuchet)
In Medieval times, the trebuchet was one of the largest, most powerful and 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.
This documentation is based on a design supplied by John Park found at Makezine.tv. His design was made with plastic piping. Great idea for Cub Scouts not so good for adults and older boys since it can not handle the inevitable stress.
Don't forget to see the original version that was made out of plastic - check it out here Plastic Teamwork Trebuchet Documentation Page
This basic design has become an upgrade of the plastic pipe design originally built by the Adults and Cub Scouts of Pack 40 (Costa Mesa, CA) and Pack 22 (Santa Ana, CA). Safety features appropriate for cub scouts and scouting events 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).
Materials
Note: this is designed with standard 2x4 in mind. Some types of wood can take more of a beating then others. Buy accordingly. All hardware should already be coated to protect against rust and the elements.
3/8 inch diameter bolt, 2 ½ inch long (qty. 14 – 1 nut and 2 washers each)
3/8 inch diameter bolt, 5 inch long (qty. 1 – 1 nut and 2 washers each)
3/8 inch diameter bolt, 8 inch long (qty. 4– 1 nut and 2 washers each) *******
½ inch diameter, fully threaded rod, 6 inch long (do not acquire an eye bolt) (qty. 2 – 2 nuts and 2 washers each)
Metal “L” Bracket 3/8 inch holes (qty. 8)
2 In. x 4 In. x 8 Ft. Dimensional Lumber (qty. 10)
Alternate: Less wasted wood (2 In. x 4 In. x 10 Ft. Dimensional Lumber (qty. 4)
2 In. x 4 In. x 8 Ft. Dimensional Lumber (qty. 2))
1-1/2 In. x 10 Ft. Galvanized or Gas pipe (Copper piping is too flexible)
Alternate (1-1/2 In. x 8 Ft. 6 In. Wooden Dowel and 1-1/2 In. x 1 Ft. Galvanized or Black Steel Pipe)
4 In. x 10 wood screws (qty. 4)
Small can red paint
Small can green paint
Small can blue paint
Small can yellow paint
Small sturdy flat bottomed bowl (Plastic or wood)
1 Used tire or bunch of rope
4 tennis balls
Tools
Saw
Miter box
Mallet or hammer
Small paint brush
Electric drill
Wood file or sandpaper
3/8 inch drill bit
½ inch drill bit
1 ½ inch drill bit
3/8 inch countersink drill bit
½ inch countersink drill bit
4 inch or larger C-clamps
Scrap wood
Cost
Approximately $100
Project Overview
The Diagram below shows the main sections of the trebuchet:
v Throwing arm (Maroon)
v Throwing arm supports (Light Blue)
v Base (Green)
v Upright assembly (Dark Blue)
Step 1: Cut the wood to length
Using a miter box to maintain straight cuts, cut the following lengths of lumber:
v 5 foot long wood 2 In. x 4 In. (8)
v 25 inch long wood 2 In. x 4 In. (2)
v 65 inch long wood 2 In. x 4 In. (2)
v 6 inch long wood 2 In. x 4 In. (2)
Step 2: Prepare the base boards
Take 4 of the 5 ft. long boards and cut notches on the ends. Make sure the notches are alternating on either side. Failure to do this may cause some weakness in the corners. You will want to cut the notches so that the boards are laying flat. Make every effort to keep your cut straight. These boards are meant to interlock. Each notch should be 1 inch deep and 4 inches wide if using the standard 2 In. x 4 In. dimensional lumber. This allows for the boards to interconnect when done. See diagram Fig. 1 and Fig 3.
Figure 1
Step 3: Finish preparing the base boards
Take the 4 previously cut boards and drill 3/8 inch holes in the ends. The holes should be centered inside the notch sections. See Diagram Fig. 2.
Figure 2
You may want to counter sink the hole for those that will be facing the ground when assembled. When countersinking your holes for the bolt head and washer make sure to do it on the same side of each of the base boards. This will help if you are on flat ground. You can skip this part if you only plan on using the trebuchet on uneven ground though it is still recommended if not necessary.
Step 4: Check the base boards
You will now want to take the 4 base boards you have prepared and do a dry fit.
The corners should fit in an overlapping fashion and the holes should line up.
You will also want to insert the bolts with washers and nuts to make sure everything fits properly. This is the time to make any adjustments if something is off a little. When everything is fitting properly disassemble all the boards and paint them green. This will color code your pieces to make it easier to assemble later.
Figure 3
Make sure to do your painting in a well ventilated location. The fumes from paint can be toxic in high concentrations.
Step 5: Prepare the Upright boards
Take 2 of the 5 ft. long boards and cut notches in one end. Make sure the notches are on the same end of each board. Failure to be consistent may make the board unusable. You want to cut the notches so that the boards are on their sides. Each notch should be 1 inch deep and 4 inches wide if using the standard 2 In. x 4 In. dimensional lumber. This allows for the boards to interconnect with the upright beam when done. See diagram Fig 4.
Figure 4
Step 6: Finish the upright boards
Grab the 2 5 ft. long boards you just notched on one end and cut a portion off the other end. You need to use your miter box to make sure the cut is at a 45º angle. The cut need to be made so that the upright sits at a 45º angle flush to the ground. This will on the opposite corner of the notch. See Diagram Fig. 5. Remove the hatched area at the bottom.
Figure 5
Now you need to drill a couple of holes in the boards for mounting purposes.
The first will be down by the corner you cut at a 45º angle. Locate a point 1 inch up from the part that was cut off and 1 inch in from the end of the board. Now Drill a 3/8 inch hole at the point you marked off. This will line up with the base later.
Take these same boards and drill a 3/8 inch hole centered in the section with the notch. This should be about 2 inches from the end and 1 inch over from the side. See Diagram Fig. 6.
Figure 6
Step 7: Create the upright beam
You will be creating notches on the ends of one of the 65 inch boards. This board will match up with the 2 boards you just got done working on. First you will create two notches on either end. Laying the board on its side cut a notch that is 1 inch deep and 2 inches wide. See Diagram Fig 7. Do the same on the other end of the board. Make sure you are cutting the notches on the same side of the board.
They will run for the entire 4 inches width of the board.
Figure 7
After that you will drill two 3/8 inch holes in the notched sections at either end. They will need to line up with the holes you previously drilled in the two upright boards.
The holes should be 1 inch in from the end and 2 inches over from the side of the board. Basically, this is centered over the two upright boards lining up with the holes previously drilled in them.
Also note that the holes will not be as centered on this one as they had been in the past. You may find some of this board creating overhang.
Step 8: Create the throwing arm supports
The next step is to create the throwing arm supports. These two 5 Ft. boards will be the main beams that hold the axle and throwing arm. Care must be taken to make sure any holes and cuts are accurate. Minor errors can make the trebuchet near impossible to assemble.
First you need to lay the boards flat and cut off a section at a 45º angle in the corner. The section removed on each board will allow it to sit flat to the base unit at a 45º angle.
Using your miter box to cut off the corner at a 45º angle starting at one corner and ending 4 inches up from the other corner. See diagram Fig. 10.
Figure 9
Step 9: Create mounting holes on throwing arm supports
We now need to put in the mounting holes for our throwing arm support.
We will deal with the holes at the top by the upright support later. Right now we are concerned with mounting the throwing arm supports to the base.
You will want to place the first of the two “L” brackets at the edge of where the angle starts at the back of the throwing arm support. See diagram Fig. 10. This will provide you a good footing on the board. The second “L” bracket should be spaced over about 1 inch or you make the decision on the spacing per the width of your “L” bracket. This will make sure your picking up a solid section of material. There will be some intense forces applied on all the supports so we want to minimize the risk of breakage.
You will drill your 3/8 inch holes at the locations marked by the “L” brackets. Makes sure to keep the holes level as much as possible. You are going to match up the brackets on the other side.
You should dry fit the 3/8 inch bolt and hardware before proceeding to make sure it all fits properly. Make any adjustments at this time.
Remember that all the bolts being used to mount the throwing arms to the base are the 3/8 inch 2 ½ inch long type not the 8 inch long ones.
Step 10: Mounting holes on base unit
At this point we have the mounting brackets attached to our throwing arm supports. Now we need to attach the “L” brackets to the base. We have to determine the center of the base first.
Acquire one of the base boards and determine the center. This should be 30 inches from either side. The throwing arm support boards will have a space of 6 inches between them to account for the width of the throwing arm at the axle.
Thus from your center point you will measure over 3 inches in each direction.
This point will be where the throwing arm supports are mounted. This marks the inner edge of each throwing arm support. Line up your throwing arm support with the “L” brackets dry fitted so you can find the locations you have to mark to drill the additional holes.
Drill the additional 3/8 inch holes at the points you have marked. There should be a total of 4 holes per throwing arm support; 2 holes per side. Make sure to countersink the holes on the underside of the board so that it will lay flat. See Diagram Fig. 11.
Step 11: Attach upright assembly to base
We need to attach the upright assembly to the base. We will need to join the upright supports and the beam before we can mount it to the base.
Measure a point in 6 inches from the end of the base. This gives you enough clearance to not hit the beam running along the back. At this point you will need to drill your 3/8 inch hole across through the base beam. You will repeat this for the other side as well. Once you have the holes drilled you can match up the upright arms and dry fit with an 8 inch 3/8 inch dia. bolt. NO need to countsink the bolt and washer anywhere in this portion. See Diagram Fig. 12.
Figure 12
Step 12: Complete the triangle
At this point in the process we have two throwing arm supports suspended in air.
We need to attach the upright support beam to them to complete the triangle.
You can now rise up the upright supports to the throwing arm supports. We need to mark the location of juncture to create a slim notch for each throwing arm support in the upright beam. This will help keep slippage down and create added support. Once we are done with this we can drill the holes and complete the triangle.
Mark off the location of the throwing arm supports on the upright beam. Do this by simply marking the side of the throwing arm supports with a pencil.
You’ll have to detach the upright support and then cut along the marked off section. You want to go either a ¼ inch or ½ inch deep along the 2 inch wide section. See Diagram Fig 13.
Figure 13
Once you have cut the notches you can remount the upright and rest it on the throwing arm supports. At this point you will want to use the C-clamps and scrap wood to secure the two parts to facilitate drilling your 3/8 inch holes. Place a piece of scrap behind the throwing arm supports and secure this to the upright with the C-clamps. This will allow you to drill straight consistent holes.
You will need to mark the mid point of the throwing arm supports and the upright where they intersect. Make sure when drilling the holes that it is lined up straight due to the odd angle of the wood. If you fail to keep things straight you will have trouble assembling the launcher and/or weaken the beam.
You should dry fit the newly drilled holes with two 8 inch 3/8 inch bolts and hardware. Make it only finger tight. See diagram Fig.14.
Figure 14
Step 13: Finishing the supports
Remove the bolts and any other fasteners from the upright supports and throwing arm supports.
Now take the upright supports and paint them yellow. The Throwing arm supports will be painted blue. Color coding the lumber will aid in assembly and also protect the wood. There is no need to color code the bolts and accompanying hardware. All the bolts should be already have a finish that will help protect against the elements.
Step 14: Build the throwing arm
The throwing arm is one of the pieces that take the most abuse. As the only moving part in this trebuchet it is of utmost importance to make the arm as precise and sturdy as possible.
The throwing arm is in essence made up of three parts: Throwing arm counter weight cross beam, rear arm, and counter weight arm.
We will first work on the counter weight arm. The counter weight arm is made up of two each pieces of lumber equal in length. Take the two pieces that are 25 inches in length and measure a point 5 inches in from the end. This point is where the 1 ½ inch axle will be placed. It needs to be centered on the board as well. Thus 5 inches in from the end and 2 inches up from the side is the location for the hole. You will need to at this point drill the 1 ½ inch hole through both boards. Metal pipe will later be inserted to form the axle. You will want to make sure the holes are smooth on the inside to avoid friction.
Now we need to measure out the locations for the fasteners that will join these parallel timbers to the rear arm. These points will be equidistant from the axel and centered. Measure a point in 2 ½ inches in from the end and 2 inches up from the side. Measure a second point 7 ½ inches in from the same end and up 2 inches from the side. We also need to countersink the ½ inch holes on each of the boards. This will only be done on one side.
Drill ½ inch holes at both these points.
See diagram Fig. 15.
Figure 15
We now can work on the rear arm since the counter weight arms have been prepared. We will do the same as we did with the counter weigh arm.
Acquire the remaining 65 inch board. Measure a point 5 inches in from the end. This point is where the 1 ½ inch axle will be placed. It needs to be centered on the board as well. Thus 5 inches in from the end and 2 inches up from the side is the location for the hole. You will need to at this point to drill the 1 ½ inch hole through the boards. Metal pipe will later be inserted to form the axle. You will want to make sure the holes are smooth on the inside to avoid friction.
Now we need to measure out the locations for the fasteners that will join this lumber to the counter weight arm. These points will be equidistant from the axel and centered. Measure a point in 2 ½ inches in from the end and 2 inches up from the side. Measure a second point 7 ½ inches in from the same end and up 2 inches from the side.
Drill ½ inch holes at both these points.
See diagram Fig. 16.
Figure 16
We can at this point do a finger tight of the rear arm and count weight arm pieces
Line up the lumber so that the 65 inch rear arm is pointing to the back and the other counter weight arms are pointing in the opposite direction.
Now use your fully threaded ½ inch bolts to fasten the two parts together. Do not mess with the axle at this point. See diagram Fig. 16.
Figure 16
Step 15: Attach counter weight cross beam
Now that we have the basic throwing arm assembled we can attach the counter weight cross beam. This is what the users of the trebuchet will secure to actuate the arm and throw a water balloon.
You need to locate a point 3 inches in from the end. This is opposite the end with the axle hole. At this point you will drill a 1 ½ inch hole in both boards.
You can test the hole by inserting your metal pipe or dowel. It should be a snug fit. You do not want it to have too much play as it will cause problems with the users.
Step 16: Attach balloon cup
The last thing needed to complete the throwing arm is to place the bowl on the end of the arm. First we will bulk up the end of the rear arm by attaching two pieces of wood to either side. We will be adding the two 6 inch long pieces of wood 2 In. x 4 In. with wood screws. To do this we will stagger our wood screws and permanently fix the pieces to the end of the arm. We are staggering the wood screws to make sure that we don’t run into problem internally on the rear arm. See diagram Fig. 18.
Figure 18
After the additional pieces have been affixed to the end of the rear arm you need to attach the bowl to the same section. If the bowl is wooden you can use wood screws to attach the material otherwise you will need to drill a 3/8 inch hole for a 3/8 inch bolt and hardware.
The hole for the bolt should be 3 inches up from the end and centered on the rear arm (1 inch in from the side). See diagram Fig. 18.
Figure 18
You will also drill a 3/8 inch hole in the middle of the bottom of the bowl. Now insert the 3/8 inch 5 inch long bolt through the bowl and then the rear arm. You can finger tight the nut for now. Later make sure to check that the nut is on securely on this and all other bolts.
Step 17: Finish off the throwing arm
Now is the time to paint all the pieces of the throwing arm. Take each part of the three pieces and paint them red. It is optional if you want to paint the dowel or metal pipe as well, though the pipe should not need to be painted.
Step 18: Final preparations to attach the throwing arm
At this point we have a completed throwing arm and we have the completed triangular base composed of the supports, and base unit. We now can proceed to attach the throwing arm to the throwing arm support.
Measure a point 3 inches down from the top of the throwing arm supports and 2 inches in from the edge. This will be the point at which we drill our axle hole.
You should have the upright assembly dry fit to the throwing arm supports and it does not hurt to reattach the C-clamps and scrap wood for additional support.
Taking care to keep the drill level, drill a 1 ½ inch hole through both supports.
You will do each separately since the space between supports is so large. There is no room for error in the holes you will be drilling. Check and double check your work. Also make sure to smooth out the inside of the holes (with sandpaper or a wood file) so the axle can move freely. See diagram Fig. 30.
Figure 20
Step 19: Attach the throwing arm
All the necessary holes have been made so that now we can insert the axle and attach the throwing arm. Due to weight issues you will likely want to have two or more people help in attaching the arm.
Begin by positioning the arm such that the 1 ½ inch axle holes all line up. This hole is located in the throwing arm supports and down the middle of the throwing arm. Once you have verified everything is lining up you can not insert the 1 ½ inch metal pipe. You may need to use a mallet or hammer to get the pipe to pass through all the pieces. The pipe needs to be centered for maximum stability and usability. Since this is a human powered trebuchet you never really know how much force will be applied by the users. Previous versions make out of plastic plumbing pipe have broken under stress.
When all has been attached the arm should move freely back and forth. There may be a little resistance in the beginning since you have a very tight fitting hole.
You may want to apply a little lubricant on the outside of the pipe if things are sticking too much.
Figure 20
Step 20: Installing bumpers
The last step to finish off our trebuchet is to attach some bumpers to the uprights. The purpose of the bumpers is to dampen the impact of the counter weight cross beam hitting the upright supports.
Cut stripes of rubber from your used tire that will cover the general section of impact. These stripes should be around 5-10 inches long. You will want to cut a stripe also for the portion of the upright that is between the throwing arm supports. These rubber stripes can be either glued or nailed down. Accuracy is not a major issue on this portion.
Also now take your two tennis balls and cut them along one side. With the slit pass them over the ends of the metal or wooden counter weight cross beam.
Do the same for the portions of the axle that overhang each throwing arm support; they pose a lesser risk but, still a risk.
Step 21: Fire when ready.
Double check at this point all your bolts. Tighten down all the nuts.
You can now load a water balloon in your bowl. The more force applied to the throwing arm counter weight beam the farther your balloon will fly. However, keep in mind as was mentioned earlier, an over zealous person can apply so much force that the cross beam can break. Breakage should not be a major issues it you are using metal piping; though it could still become bent and unusable. You may find the hardware loosening over time so a periodic check will be necessary.
One other advantage of this design in comparison to the plastic pipe version is its weight. Due to the added weight of the wooden beams you will find it tends to stay on the ground and not jump or buck as much during use.
1. Position your hands such that it does not get pinched against the throwing arm or upright supports when you push down. The counter weight cross beam helps with this issue.
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. Create a safety zone.
- Be careful when you are positioning the 1 ½ pipe that attaches the throwing arm to the throwing arm supports. You may need to use a mallet or hammer to get the axle into position.
don't forget to see the original version that was made out of plastic - check it out here Plastic Teamwork Trebuchet Documentation Page
Trebuchet resources and documentation
Use the video at the following link as reference. Our launcher is based on this one. Though through experience and experimentation we changed the materials to wood from plastic pipe so that would not break as easily. http://www.wonderhowto.com/how-to-build-huge-trebuchet-that-flings-water-balloons-272344/
Makezine video of Pipe Trebuchet construction
The Treb Challenge – Globalspec. Nice game to learn workings and physics behind trebuchet.
Web site to the NOVA program "Medieval Siege," which covers making a replica of Warwolf. Warwolf was commissioned order of King Edward Longshanks of England, during the siege of Stirling Castle, as part of the Scottish Wars of Independence. Part of the NOVA series Secrets of Lost Empires,
Real Trebuchet Plans – Wooden fully working
Ideas for use of the Trebuchet in the Den and Pack Meetings
Ø Have scouts work out designs for a balloon launcher – you will see very creative designs, not all of which may work.
Ø Have scouts make miniature version of a catapult or Trebuchet
¯ Have a marshmallow war at Pack meeting
¯ You should do both a distance and accuracy requirement
Ø Have a build party / work day
¯ This can be in place of a pack meeting or in addition to depending on unit size.
