Introduction: MURLIN Trebuchet

About: Hi, I'm a student trying whatever peaks my interests. Most of the things I try are for my pure enjoyment as well as hoping they help further and broaden my future endeavors. Caeser cipher:17

Catapults have been in use since ancient times and have been proven to be some of the most effective large scale weapons of its time. One type of catapult is the Trebuchet, one of the most powerful catapults to be employed during the Middle Ages. The trebuchet began to surface around the 12th century in the Mediterranean in both Christian and Muslim lands. It is noted that they would typically fire projectiles, usually large stones/rocks upwards of 300 lb or more. Trebuchets were used to launch said projectiles at castle walls to destroy them, with great effect. Trebuchets were still used well into the 15th century, long after firearms and cannons (gunpowder) were being used in force during the 13th-14th century. After the use of gunpowder, the trebuchet and catapults as a whole began to retire as formidable weapons, only reappearing from time to time briefly.
Today, they are typically used for recreation and education, although since the Syrian Civil War in 2013 and during certain riots in the Ukraine in 2014, trebuchets have resurfaced as weapons. However this time - they fling explosives. And that brings us to our recreational and educational project - but unfortunately no explosives. A friend and I volunteered to build a trebuchet to compete against a local high school. Following some research, we decided to build a MURLIN (Multi-Radius Linear Nodes) trebuchet, following research based off of Leonard Vance's designs, testing, and videos that he was so generous to share with us. So here is how we built our version of the MURLIN trebuchet.

Sources: (for the special instructions and help) (for basic information)

Note: Most if not all of the dimensions for the throwing arm will be expunged due to privacy and copyright concerns, for Mr. Vance did not wish for the plans to be publicly published because the plans were part of his intellectual property. The one we based off ours of was the 8 foot MURLIN Trebuchet to fling baseballs. Ours is 4 feet and flings golfballs, basically halving the design. You will have to personally ask/email him for the throwing arm blueprints. Here are the conditions:
1) You agree not to distribute the plans to anyone else without his permission
2) You let Mr. Vance know how building and testing go.
Plan requests should go to

Step 1: Primer Paso: Juntar Materiales

First, you'll want to gather all the necessary tools and materials. To do this, you will need everything listed below. Some of the materials can be subject to change depending on how you want to build your trebuchet. Smaller trebuchet, smaller proportions for everything. I will list what I used. This is no simple wood gluing project, nor part of your average scrapbook routine. There will be heavy machinery and power tools used, which will require safety precautions. So first and foremost, grab a pair of safety glasses, maybe some gloves and get to the workshop.

What You Need:

- 2x4" planks - Lots of 'em (pressure treated preferably to prevent warping of the wood)
Frame: (2x4's)
- 4x - 4.5" - 2x - 1' 5.5"
- 4x - 7" - 4x - 3' 3"
- 2x - 6.75" - 2x - 4'
- 6x - 9"

Arm: (1x0.5" planks cut from 2x4s, 1 each for those unmarked)




Nuts & Bolts:*
- 4x -1/4th" fully threaded bolts or rods at least 3.5" in length
- 1x - 1/4th" bolt at least 1" in length
- 17x - nuts to accommodate said bolts & rods
- 3x - washers, ditto
- 6x - 3/8th" fully threaded bolts at least 5" in length
- 1x - 3/8th" fully threaded rod at least 1' 8.5" in length
- 10x - nuts to accommodate said bolts & rods
- 50x - washers, ditto
- 1x - 5/8th" fully threaded rod at least 1' 8.5" in length
- 1x - 5/8th" wide metal tubing to reduce grinding of wood on the threaded rod
- 2x - nuts to accommodate said rod
- 6x - washers, ditto
- A PVC pipe cut in half (your choice in diameter, as long as it fits whatever you are firing)**
- 1/2in sheet of plywood, 1x2'
- Tools & heavy machinery (table saws, band saws) to drill, cut, or make holes in wood.
- Adhesives: wood glue, hot glue, super glue, epoxy
- 200lb+ Kevlar cord - cut accordingly
- Elastic band to go around projectile to be used as a sling
- 2 Pulleys for 3/8th" rod
- CW (counter weight) and weight holding device
- weight plates, eyebolts, plate of metal used for backing, washers, nut, and PVC or metal spacer tube
- Various bits and pieces of metal to be used as a trigger catch and for reinforcing the trebuchet
- Somewhere to fire it, preferably a football field or larger area.

Proximate Costs of Project:
Most of the project material was either cannibalized from past projects or found laying around in my garage or in the workshop. Pricing of material depending on area also differentiates, thus accurate cost of all materials could not be determined, however I will provide an estimate of the costs as well as those we know the price of.
$13 of wood - 8" lengths of 2x4"s ~ $3 per length
~ $20 ± $4 of nuts, bolts, washers, rods and other bits of metal
$32.50 of Kevlar rope ~$3.62 per foot

All the other cannibalized material ~ $25
Total: ~$92.50, excluding electricity, labor, time, and tools to build.
This is the pricing of our trebuchet. Yours will depend on what you do with it and how.

*note - most if not all bolts can be replaced by screws, I designed the trebuchet to be collapsible as a way to fit it into a car for transport. For your ease, you can make it fixed, and attach the frame and arm together using screws.

**note, this trebuchet is meant for a golf ball or something similar in size. A baseball is max. This trebuchet cannot and will not fire: Pumpkins, bowling balls, basketballs, human beings/living objects(please don't do this regardless of what trebuchet/catapult it is), or anything larger or heavier than a baseball.

Step 2: Étape 2: Le Cadre

Once you've gathered all your materials, the next part is building The Frame. The trebuchet was conceived with help from Leonard Vance's blueprints for his MURLIN trebuchet, although we modified and changed half of the aspects for our uses. I used the measurements from his blueprints, halved them and then changed whatever I needed. Then I set out to design the trebuchet I wanted using a CAD program, the free Google Sketchup program, as you can see above. I then set out to build it.

To start off with the base, glue and/or screw the 3'3"(B) boards onto the two 1' 5.5" (D) boards, with the pieces ending exactly at the long edges width-wise of each board (refer to pictures). Attach the boards 0.5" from the short edge of the 1'5.5"(D) boards. This is the base of the trebuchet.

Now to the triangular frame. The longest length of 2x4 will be the main "arm" of the frame. These two particular lengths are leaned back on top of the bottom shorter arms, and suspended above it using the 7" pieces of wood on each side of the 4' long 2x4's. The frame itself is an equilateral triangle. All of the inside corners of the triangle frame will be 60°. Refer to the photos for clarification. The last two 3'3"(C) planks will prop up the 4'(A) plank, on the outside of the bottom 3'3"(B) plank and the 4'(A) plank. (C) should meet (A) at the 1' mark from the top of (A). You can either drill holes and put bolts into where they meet, or glue and then put screws into them. But before you do this, drill the holes for the arm and the pulleys before making the frame permanent - that is unless you use bolts and can pull it apart easily.
From the top of (A), glue the 9" 2x4 onto (A). Then the 6.75" on top of the 9". And finally the 4.5" on top of that. See picture 4 for visualization. Do the same for the other (A). At the midpoint of (A), glue two 9" on top of each other, and then onto the midpoint of (A). Make sure it is centered. Then center the last two 4.5" blocks onto top of the stacked 9" blocks and glue that as well. Let these dry properly before drilling into them.

Finally, drilling the holes for where the rods will go. Halfway down (A) where the protrusions of (A) for the arm are, drill a centered 5/8th" hole for each arm. At the top of (A) where the first protrusions are, drill a centered hole for a 3/8th" rod.

Step 3: The Throwing Arm

The throwing arm is the most complicated part of the trebuchet. If something is wrong with it, many things can go wrong. This is the main reason why I asked Mr. Vance for blueprints to understand how to properly make the arm. Based on my design, you will need the pieces of 1x2" wood of lengths: [DATA EXPUNGED] for the arm. In the above pictures you will see how the plate is made, as well as the internals of the the arm and how each of the throwing arms are positioned. Please use that as a reference. The degrees from which they are turned are shown in the image 3. Specifics must be requested from Mr. Vance, with his contact info provided in the intro. The math and determination to get the info involved is up to you.

The plate that holds the throwing arm pieces is made of 1/2" plywood, cut into 1x1' squares. Using completely flat, straight pieces is highly advised. Plans for said plates are shown in images 1 through 4. After making the plates, use wood glue to attach the 3 throwing arms and the piece to hold the projectile (for this piece, I would advise screwing down the PVC half-pipe onto it first, then gluing it down). After gluing all the pieces into place, place the 2nd plywood plate on top. Make sure the markings for the lines are still there so you can drill a hole through it later. After the glue dries, screw the plate down to make sure all the arms and plate are sturdy and secure. Then, drill a 5/8th" hole in the center where all the lines intersect. Widen if needed, and then glue and insert a length of the 5/8th" metal tube/spacer about 5 5/16" long through the hole. This is where the arm will be mounted on and spin on the 5/8th" rod that goes through the frame.

Afterwards, glue the 1x1x0.5" blocks onto the ends of the 4 marked throwing arms. Drill 1/4th" holes through each and put the 1/4th" bolts into them. On each side of the bolts, screw on one nut, then a 3/8th" washer, and then another nut. Repeat for every side and each arm with the blocks on it. These are the guides for the kevlar rope attached to the CW. In picture 2 it will show you how to bolt down the catch for the sling rope. And to the right of it, the hole you need to drill to thread the sling rope through. Make sure the sling rope is long enough to go though the hole, go to the end of the PVC half-pipe, make a "U-Turn" that goes around the projectile and back to the catch. Once you get to the catch, tie a loop/knot that is loose enough to be released easily but small enough to go around the metal stock. Cut off any excess rope. Now, at the point where the "U-Turn" is, sew the elastic band (that should fit around the projectile/ball) to the rope. Give enough slack at the bend of the rope so that the ball can rest within it, and the band will be exactly at the equator of the ball. See images 5-7. Do not glue down the rope until you are sure the pouch/sling works well. The only way to tell is by testing it. After you are sure it is perfect, glue the rope to the pouch to secure it.

Step 4: The Flux Capacitor

As for the CW (counter weight) mechanism, there are 3 parts. The weight holding part, the rope attaching the CW to the arm, and gravity. To build the CW holder, refer to the last photo. I did figure that bit out on my own, however Mr. Vance had already provided a perfect picture for it, and I just had to use it. Cut about 9" of kevlar or weight tested rope for your trebuchet. Loop it evenly with the CW at the midpoint.
Insert the 3/8th" rod into the top hole for the pulleys. In the picture, you can see that I used a ton of washers as spacers for the pulleys. When you insert the rod and get to the center, put 16 washers onto it, then one pulley, then 2 nuts, another pulley and 16 more washers. This should keep the pulleys straight and prevent them from spreading apart or getting too close together. Secure both ends of the top (A) frame.
Insert the 5/8th" rod into the midpoint hole for the arm as seen in image 3. Referring to the previous procedure, when you get to the center, put 2 washers on, and then the arm, then another 2 washers on the other side, and push all the way through. Fasten the threaded rod like before.
And finally (really), with some help, feed the 2 ends from the CW over the pulleys (so that the CW is pulled all the way up), over the guides of the throwing arm, and tie it with a basic knot onto the main (the longest part) arm. Using the leftover slack, loop each side under the metal tubing and over the plywood plating. Tie a sturdy knot (whatever you choose), and cut off the excess. Refer to image 3 again. Slowly and gently guide the arm into a non-armed position, where the CW should be on the ground at this point.

Note: In the first picture, you will see a metal brace covering the top corner of the trebuchet, as well as two bungie cords going across it. That is optional, and I did that to make sure the sling did not get caught in the pulleys when it fired.

Step 5: Time & Effort Analysis

The total time required to build the trebuchet was not very taxing, based on how we built it. We built it over a couple months time, working on it a couple hours every day. If we were to get down to business and put all our heart and soul into it, it would take roughly 1 month to complete, taking into account the gathering of materials, time spent drilling, cutting, gluing etc.

However if you were to follow step by step instructions like this, it would go by much quicker. The reason it took us so long was because we had to think of and calculate a plethora of factors into the building of the trebuchet. I also had to engage into discussions and conversation with Mr. Leonard Vance to attain the basis for the design all the way up until the publishing of the Instructable as to agree with his conditions of using his ideas.

Step 6: Improvements

To improve this project, we could work a little more effort into the precise measurements of the trebuchet and try to fine tune it to improve the firing of it. By doing this we can improve the overall efficiency of the energy use in the trebuchet and prevent losing any potential velocity. We could also paint the trebuchet and the golf balls with flames to make them go faster. The difficulty of these would not at all be difficult, but maybe time consuming and for certain ones - futile.

Step 7: TESTING!

Videos of testing, the former is slow-mo via GoPro Hero+ Silver, the other is from my phone