Trebuchet of the large variety (a work in progress), 4.28.07 update

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This is my second wooden, hanging counterweight trebuchet and the first well-documented one. It will be bolted together from many self-designed and self-constructed components, each about six feet in length. Hopefully, that strategy will allow for some degree of siege mobility and make fixing broken sections of the device far easier. Oh yeah, a trebuchet is a medieval-era siege weapon capable of hurling a variety of things great distances, inducing feelings of pleasure (in me anyways).

I want to hear your trebuchet tips! This project is just starting and will be updated gradually as things progress; I'm sure there's some latent treb-knowledge in the heads of many Instructablers. Let me know what you think of current plans and where you'd like to see the trebuchet go. Favorite arm-ratios, clever trigger systems, winching mechanisms, sling designs...I'd love to try implementing them. I've never attempted a large scale floating arm trebuchet, but if you're convincing enough, I just might. If you'd like to be a collaborator, let me know and I'll try to add you on.

Also, I'm an enormous SketchUp fan. I'll try to present screenshots of any models I use but viewing and helping with this Instructable will be easier if you just download the (free) software here.

This page will also carry the breakdown of the trebuchet's cost (see the Excel file below). As of my last expenditure on April 27, 2007 I've spent $315.

This here Intro page will be the resting spot for the most current model of the entire trebuchet.

A warning to fellow siege engineers: This project can be considerably dangerous, given the gravitational energy of these things and the fact that it is a weapon. Exercise great caution if you decide to build a trebuchet of any size--smaller models (like this) should be attempted first to get a sense of their operation.

Last note! The Sourpuss Trebuchet is a major inspiration to this project; a final product half as good as their device would be incredibly pleasing. The Dr. Seuss Treb should also be cited for it's poetic awesomeness.

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I am building a trebuchet at the moment and need sopme more infor on the frame of the base i did a quick test fire and it ranged from 20-50 metresdepending on the lenth of the sling and the countwer weight
Qwerty.077 years ago
In about yr8 so i was about 13-14 i build a trebuchet that with the arm totally vertical it would have been about 1.5m high(3-4ft) and yer i figured out throught my own calculations that 1:9 is the golden ratio for the whole thing 1:10 also works good. 1:9 is applied to the arm length and the wieght ration so plan how much what you intend to through ways then base your design on that. there is also another issue as you whiether you want to use the some sling ever time or have idividual slings. if you don't know what i mean you can either have a fixed sling which means that one part is attched to the arm and the other is only hooked so when the arm reached the de-ttach point it un hooks releasing the ammuntion i find this is a bit to mess around with so i went the other option. on mine i had a hook that the end of the arm it looked like this: / / | | | i hope you get the picture and yer i attached a chain to a tennis ball that the chain hooked on to the hook (no duh) and yer i also realised the the weight ratio was out so i added bits of lead i cut from a sheet to sum up the differents and you realise that the heavier ball went about 3-4 times feirther so yer i hope i helped you feel free to ask me about my project and i would like to see how your trebuchet turns out.
your calculations are wrong sorry to sink your ship they are waaaaaaaaaaaay off
Vertigo6667 years ago
2:1 arm ratio, with the shorter part on the counterweight side. i think.
nononononoNO it is better with 5:1
StepsoftheSun (author)  Vertigo6667 years ago
I think I'll have to take a poll on the ideal arm ratio (I think the physics may be beyond me). Your suggestion is the lowest I've heard yet--it's gone as high as 5.5:1...
5.5?! maybe 5:2...
the ideal ratio is 4:1I was watching scrap heap challenge (throwing scooters) and the guy who was one of the experts said that the ideal ratio is 4:1 and the judge said 100-150 times the mass of the object which you are throwing on the counterweight end (the shorter one)
Well, the second bit about the mass isn't on the site but I remember it from the show
abehambino5 years ago
Have yet to build a trebuchet but have done quite a bit of research on them. what I do know about distance of the counterweight and such is that the ratio of counterweight to ammo should be the same as the ratio of of the length of the counterweight arm and the length of the longer arm(the name slips my mind). Hope this is helpful. I have plenty of more ideas I am working on and would be glad to give advice. Just let me know what you need.
you are wrong there mister
tjlavelle3 years ago
I built one of those with a simpler design than yours. I used cinder blocks for the counterweight (about 200 LBS of them) and it can throw about 250 feet with a 1 LB projectile and im not done testing it yet. it cost me about $50 in lumber and screws. mine is a free swinging counterweight with fixed base trebuchet. It has a frame of an equilateral triangular prism with side lengths of 8' and a depth of 4'. The throwing arm is 15' and the main weight arm is 3'. The metal bar I used was a circular fence post. If you want more information on building and tips on design, contact me at By the way, I would reinforce the throwing arm if I were you, my first one was a similar design and it broke pretty quickly. I can give you a better design if you like that uses 6 8-foot 2X4s. Remember to keep the release angle so that it releases at 45 degrees from the ground for maximum range. By the way, you spent a ridiculously large amount of money. Low grade 2X4 is strong enough if you use equilateral triangles. If I had bought all the materials for my treb, I would have spent at most $80. Please contact me, I will be happy to help you as much as I can!
for projectile weight to counterweight weight use a ratio of 136 to 1 or, if you have a heavy throwing arm, at least 200 to 1

by the way, sorry for all the replies to myself, i just keep thinking of new tips and i have so many more to share so contact me
by the way STOP USING NAILS NOW AND SWITCH TO SCREWS or the treb will be much weaker
a ratio for throwing arm is 5:1 for max range

you can smash up the cinder blocks like i did for higher density or just use rocks

for axel hole on the arm cut a square into the arm 1/2 inch larger than the diameter of the arm and attach more boards to seal up the hole

the axel holes on the supports can be made by buying some huge screws about 3/4 inch thick and attaching them parallel to the ground just under the top of the support structure and then just resting the axel on top of these screws. This is what I did for my treb

as long as you have a free swinging counterweight treb, you should not use wheels, they will actually be detrimental to the range as long as you use the free swinging counterweight design.
action pig3 years ago
Very cool!
for my counter weight i am using 3 garage door springs that are attached to the bottome and when arm is down they are almost to critical expansion
arveyda4 years ago
My middle school students chose this as the design for their final project (they are an ambitious bunch! :-) ). I will post some shots if it is successful. Thanks for inspiring my th, th, and 8th graders!
will-i-am5 years ago
Definitely like your use of wood joints; old school strength.
spaten05 years ago
Um what is a good counter wieght if ur in the woods find a downed tree and cut it up the logs will be heavy lol
ace1175 years ago
the longer the arm with the counterweight is the slower the trebuchet will swing, for adjustable range I would make several attachment holes and then test it to see what the range is, the further from the fulcrum you go, the less range you get in the end. if you don't understand this tell me and I will explain in further detail.
aalva93 ace1175 years ago
id like to know how this goes im doing a physics project with some friends and this would help alot
dougmhz6 years ago
First off this is an interesting site and I have already found useful info in reading through this post.
I have a trebuchet that I am working on and trying to maximize.
My end goal is to throw something 300 feet on the fly. It can be anything.
I am using baseballs and softballs right now, both of which weigh 8oz. if I am not mistaken.

Here are my current dimensions.

total arm length = 6.8' (81.6)
short arm length = 1.36' (16.32)
long arm length = 5.44' (65.28)
sling length approx. 5' ( the sling pouch is right underneath the CW when cocked.)
CW box is a 16 cube and is free hanging with 8' drop form anchor to short arm to top of the box.
I have 100lbs of sand in the box and the box weighs about 20lbs or more.
My axel height is 46.

Right now it is throwing baseballs and softballs about 120 feet.
I very well may have to go bigger to get the distance I want but does anyone have any thoughts on maximizing this contraption? I saw the post about not putting the wooden arm directly on the metal axel and I will try to create a bushing with another section of pipe soon.
I m posting a picture of the little beast along and a close up of my trigger which I found inspiration for elsewhere on the web. I have wheels on here but I seriously need to remount them more sturdily so they don't allow the frame to squash down and drag ground.

Keep up the good work.
for max distance you will want something such as large lead fishing weights
DavidMF dougmhz6 years ago
Axel grease... Use liberally at your rotation point. I built a trebuchet when i was in 6th grade and i used metal on wood also with some axel grease the baby was so much more efficient.
For SCA or LARP groups using a trebuchet as artillary I would like to point out that it would be more of a supression device than team killer. (load multiple projectiles in the sling)
arrowcrest5 years ago
how are you supposed to make the arm, counterweight, and release mechanism? this thing needs to be finished. besides that, this is a very great instructable, keep up the good work.
Kilsmer6 years ago
i dont know if anyone has pointed this out before, but if you put the trebuchet on wheels it throws things further, when the couter weight moves it causes the whole thing to rock backwards then forwards and for some reason it gives it extra power.
temp Kilsmer6 years ago
that's because the weight is falling more vertically with less side to side movement. This makes it more efficient.
Techwiz126 years ago
Hey by any chance did you use google sketchUp
Ya i made a trebuchet without wheels and it tore itself apart it was pretty epic
Billythekid6 years ago
can that launch people??
willy_Nilly6 years ago
Found this and played with it a little. Looks cool. I suppose it's accurate. I hope this helps. Keep up the good work!!!
dougmhz6 years ago
I added a bushing to my arm using a convenient piece of conduit connector I found at Menards today. I greased the inside of the bushing and put it all back together. After a quick and dirty job of leveling the rig I started flinging. I probably got somewhere into the 150 -160 foot range after this adjustment. That is on the order of a 25% increase in range/efficiency which I suppose is nice return on what little work I actually did. My next project is to get some useful wheels on the beast and see what that does. If that pays off I may scale it up and see what I get. The frame is getting kind of sad anyways and will probably force me into action sooner or later. After all it is only constructed out of a pallet and pallet pieces along with some other scrap.
surfreak7 years ago
Is that just metal on wood for the axle-throwing arm connection? Definitely overdrill the hole in the arm and pound in some pipe that fits over the throwing arm for strength and less friction. I can't tell if you've already done this from your pictures, but it definitely makes a difference in range. PLUS you can lube it.
surfreak7 years ago
I haven't built anything huge (mostly small, efficient ones for competition), but these sites have a LOT of good info:

Metal to concrete blocks could work, as long as the metal is denser than the concrete (which shouln't be hard). Old lead tire weights from a tire shop should be free and work well. You might be able to get away with old tires for the wheels if you built a support for the inside. Wood circles or large oil drums/cans to support the rubber? Just throwing out ideas here.

On the axle, it doesn't have to be perfect. The looser it is the farther it'll throw (less friction). But the tighter it is, the more precise the machine will be (read: accurate). If the axle is a litle crooked it won't really affect it. You can compensate by angling the throwing arm hole if it gets to be an issue.

But I'd definitely say that a massive Floating Arm Trebuchet is in order. Those things rule. I built one for competition that used 1/2 the cw and was 3/4 the size of an older, "standard" treb, and it threw twice as far. Definitely check out the ripcord site, though. Ridiculous amount of information and treb theory.
KDwightBAB7 years ago
very nice, my friend and i was going to build one about six feet tall. but yours looks sweet
kidengineer7 years ago
holy crap thats huge!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
hedgiehog7 years ago
Ya i'm making a new trebuchet, well it's a bricole. I found all the wood on the curb, the centre post is a 7' 6x6 the thing is huge...anyway stepsofthesun, how did u load, cock and fire your big trebuchet?
Vendigroth7 years ago
what sort of range do you get? and how heavy are the things you're throwing?
StepsoftheSun (author)  Vendigroth7 years ago
With the old trebuchet, we were tossing 2.5lb water bottles (sometimes several at once) about 200-250ft up a slight hill. We used about 320lb of counterweight before the thing broke. The range is nothing spectacular but I now understand a lot of the mistakes we made during the build. The arm ratio and lengths were not correct and making the counterweight box's clearance an excessive two feet were some big errors. The new treb should do much better (and throw, hopefully, watermelons and other assorted fruit).
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