Emma (guest) 18 Mar 2025 18:47
I have to build a trebuchet for a school competition. What would be the best option, considering I am a high school student? The competition is in about two months and is graded on reaching 50 meters and precision (the center will be 35 meters). Please help me :)
The answer to most of these really depends on the specifics, but in general my advice is to keep the plane of rotation clear. Trebuchets, and pretty much anything with a sling, can throw backwards almost as far as it can throw forwards if mis-adjusted. I had a treb with a 300 foot range thrown well over 100 feet backward once when the sling failed for example.
Generally (but not quite always) if something breaks, the scary bits stay roughly in the plane of rotation. If the arm breaks for example, the projectile could easily go straight up or backwards, along with chunks of the arm and sling. Its pretty unlikely for anything to go straight sideways, though things that go almost straight up can fall down next to the treb. I generally envision the danger zone as an hourglass shape: thin around the center of the machine (axle) but widening the further down range or behind it you go.
Thus generally I try and keep almost as much space free behind as in-front, always stay to the side when working on a machine with any stored energy (counterweight not at the bottom for trebs). When ever possible avoid putting anything in the path of the counterweight or arm except when absolutely necessary, and have a safety in place when doing so (ex: loading the sling) that physically blocks the arm from moving in case of a trigger or winch failure (this is usually required by the rules of competition, and for good reason: its great practice to have a redundant safety). When ever possible (and for sure when firing) stay far enough back to the side that there is no chance the sling could even come close if whipping around.
Another thing to watch our for are winches. If you have a home made winch, if the ratchet breaks, or gets set to free wheeling mode, or you slip off the handle, you can very easily get a winch handle spinning really fast breaking you hands. Having a high quality ratchet, and be ready to just pull your hands back and back away to the side should anything go wrong while winching is a good idea. Always remember where the stored energy is, and how it could break loose and get you so you are prepared to just back away and let what ever happens happen if something goes wrong instead of having to think about it when something starts failing.
Should something go wrong (or right when actually firing it), hopefully you are to the side. Generally back away further to the side if you can so that if anything went straight up, you have more clearance before it comes down.
For small trebs, safety glasses are all the PPE I used: shattering wood or metal could easily take out an eye. Similar to working with a lathe, I always felt gloves might be more of a risk to get caught in something that to protect me. For larger machines a hard hat is a great choice. While it likely won't save you from an errant projectile direct hit, it helps communicate to others that its dangerous and the area nearby is only for people who are protected and know what they are doing, and it can save you from some things (like a ring from the sling to the head, or a glancing blow from a projectile). I did have a metal pulley shatter once: safety and a hard hat are pretty good against that kind of debris.
For more specifics, its really hard to give clear safe answers. Starting with low counter weights, safer projectiles, no spectators and ideally smaller model machines and/or simulations can really help you get a sense for the risks while keeping safe. Work your way up to higher risk situations carefully so you will be able to evaluate them better. Hopefully such an approach can get you a better sense of how big of margins are needed. Most large trebuchets tend to have low enough mass ratios that 300 arm lengths is easily enough, but it really depends on the details (drop height, mass ratio, how much roll is possible etc), so in some extreme cases that might not be enough, and in some other extreme cases is far more than necessary. Looking at total stored energy in the treb and computing how far it could throw if 100 percent efficient could give you a rough upper bound (after accounting for rolling), though most designs won't even get close to that.
I personally haven't operated any really large trebuchets, and I can never really know how lucky I got to come out of almost everything safely (one assistant got a bloody finger when hit by a broken pulley once), so I can't really give any high confidence or athoriative advice, but hopefully this, and some careful thinking and planning, can help you operate safely. Good luck, and may the stored energy leave your systems in a safe manner!
When building and operating a trebuchet, especially a larger one, what are some reasonable precautions and requirements for the range? With emphasis on the unexpected.
I can see:
aaaaa (guest) 01 Apr 2022 16:02
This page is completely non formatted correctly looking at the other pages.
Looks like my old site is down and I just linked it from there. I guess that what happens when I just leave something on a server for 10 years and don't pay attention.
You can view an old copy thanks to the fantastic internet archive project here: https://web.archive.org/web/20080611155243/http://www.spincraftsoftware.com/Files/MyHurl/HurlingBeliefEssay.html
(guest) 27 Nov 2018 15:13
i am trying to do a school project and would like to know the benefits of hurling. unfortunately, the link on the introduction page that links to "Craig's Essay on the benefits of hurling" does not work. i was wondering if there was any way to see the benefits of hurling.
All I know about them is some anonymous user authored the baka page.
From the description I can infer that if it achieves CW or arm stall it would have to be with the CW well in front of the axle (or it would hit the ground), and has a short arm rotation (angle wise), which explains why it only works well for low mass ratios.
It shouldn't be very hard to make one in a simulator if you want to see how they work. To help you get started I added a really horrible simulation of one to the baka page.
I see reference to the BAKA but I cannot seem to find any good pics/video anywhere. Can anyone direct me to some good spots?
Thanks in advance!
Most trebuchets throw a distance much longer than their release height, so its not really significant. (Ex: A couple of my throw a distance over 50 times their release height)
Typically difficult to model factors like aerodynamic drag (on the sling and projectile) and projectile spin are actually far more important.
In an ideal friction-less vacuum when throwing on flat ground in uniform gravity, the optimal throw from ground level is at 45 degrees. If your throwing from higher, the optimal angle will be a bit lower.
Assuming you you have a low drag sling (so its less of an issue than projectile drag) you will typically want to throw below 45 degrees anyway, and ideally with top spin. This is because aerodynamic drag on the projectile becomes a large factor for most typical trebuchets sizes and projectiles.
Note that for a particular trebushet, especially a poorly tuned one (ex bad arm ratio, or sling length) you may be able to get far more energy into the projectile throwing at some otherwise horrible angle. Optimal throwing angles in terms of distance for the energy really only come into play once you have a well tuned machine that is getting all the available energy into the projectile.
Its also worth noting that rather extreme machines often have rather strange tuning effects. For example some very large trebushets throwing pumpkins are basically unaffected by projectile weight: their arm speed is not effected by the sling significantly. Thus the arm swings right through where you would want arm stall, and they benefit from longer slings and later releases.
Anyway, release height is almost always going to be a bit less than long arm length + axle height + sling length if the trebuchet is anywhere near well tuned. In an optimal case the arm is nearly stopped at release, and pointing almost vertically, so you can consider the projectile to be going in a circle around the end of the arm, and use a bit of trigonometry to get a more accurate height.
I recommend looking at videos of trebuchets and pausing them at release. Looking at the first two frames after release tell you the angle (and velocity) of the throw and release position. For similar and well tuned trebuchets, the positioning is always nearly the same.
Does anyone know if there is a function for the height of release of a projectile in terms of angle of release and trebuchet dimensions for a counterweight trebuchet. Any help would be much appreciated
Thanks
Streetta
A new forum is now up to fill the void of TheHurl.org. Come on over to hurlingforums.com. A bunch of the old guard from TheHurl have made the move already.
Quite some time ago, Ron Toms (who ran thehurl.org) had to close down account creation due to an issue (I think it was spam). There were also performance issues with the site, and eventually it was shutdown because Ron no longer was willing to donate the time and resources to keep it alive. There may have been other problems leading to its end as well, I'm unclear on the details. It's unfortunate that it had to come to an end, but at least we were given such a great place for so long.
I didn't use the site much during its final few years, so I can't say much more than that. I wish I had saved the farewell message Ron posted before it was taken down around thanksgiving last year.
Anybody know what happened the thehurl.org?
Thats news to me, but it does seem to be the case. Thats too bad really. My ~8 year old account there is fine, but it seems like you are stuck since you don't have one.
Some time when I have more time, I may try and check whats up with that, since I don't see any updates on the issue in almost a year.
thanks for the input. yeah that counterweight bar was our restriction. we actually did put some weights in the middle but the track width prohibited how many. Solid bar — its a necessity really.
now as far as the hurl.org, i tried that but there didnt seem to be a way to register, and i crawled into the help section, seems to say new user registration is disabled… is there a secret trick?
Looks nice. I don't see anything horribly wrong with it (which is somewhat rare for first projects, well done).
I'd guess you could get some more range with a lower area sling. It looks like yours has quite a lot of drag. Tuning looks pretty good, but I haven't worked with an F2K personally. I can't say for sure, but maybe a higher arm ratio might have helped get some of the counter weight energy out before the very bottom, for perhaps better range and less stress on the counterweight bar. Thats mostly a guess on my part though.
Note that the energy that went into bending your counterweight bar (assuming a stronger one, and proper tuning) could have gone into the throw.
A forked SA (put some of the weights in the middle) would have reduced the stress on the counterweight bar quite a bit, which looked like it ended up being the limiting factor. Its also possible to spread the counterweight across multiple shorter bars, which can make finding strong enough bars easier.
Your trigger design is interesting. I haven't seen one like that before, but looks like it does its job. Well done and I'm glad you guys had fun! Thanks for sharing.
Its mostly just me on the forums here; there is a much larger and more active community of even more knowledgeable folks over at www.thehurl.org forums.
watch?v=AWfyvWsa3zc
search this string in youtube, please.
the link above is a series of fires with a treb the Cal Lab built in our off-time built for a Subbase New London Morale boosting event.
We had a ton of fun doing it. Especially since we all work in the electronics field and got to wrap our heads around a mechanical, physical problem.
Throwing arm is 8 ft. 105" weight drop of 195 lbs (I think underpowered but out bar was 1/2" blackiron pipe, maxed out). axle is 2.75 feet from weighted end. After tuning (you can see a couple shots go not so well in the first part of vid) sling length was 6 ft., release pin at about a 50 degree angle. Max distance was 67 yards by laser rangefinder and spotter.
So it was the first time we did something like this, and we got outshot by only one of the other trebuchets, who had the full 15 ft throwing arm and 750 lbs of counterweight allowed in the rules, not too bad.
Wanted to share this beast and look for some constructive criticism. enjoy, and fire away.
Use a simulator to work out things like the hanger length, arm ratio, sling length etc.
Looks like your mass ratio is ~37.5:1. Thats pretty low (Normal is ~100:1, which would mean 3 pound ammo here), so I'd guess, especially given that you have wheels, that you will get better results with a fixed counterweight than a hinged one. Either way, you will want a pretty low arm ratio, maybe even as low as 2:1 ( A simulator should help greatly here).
Also, personally I've found fixed counterweight trebuchets simpler to tune (and to work better when poorly tuned), but its been a long time since I worked with either type.
Anyway, I strongly recommend checking out a simulator of some kind. It will let you get a good sense of what dimensions to choose, and what adjustments have what effects.
Sadly I haven't kept this site very up to date, so there might be some newer/better simulators around. If you find any, feel free to add them to the simulators page.
Lastly, its mostly just me here. You will get lots more great advice at the The Hurl Message Board. Especially if you want structural advice, you will get much better help there, since I haven't built anything very strong at that scale, and many of them have.
Good luck, and stay safe! A treb that size can be pretty dangerous (Remember, you are very likely to throw backwards, or trigger unexpectedly for example!)
Building 8' tall HCW. Have 14' solid red oak 2"x8" for TA which I plan on tapering from 8" to 3". I have 300 lbs weight available. Want to throw jugs of water about 8lbs. Pls help with ratio. Where to drill axel, where to hang CW. Any other info I need please. I'm ready to taper TA. Have frame already built. 40" wide, 8' long, 8' high on 12" wheels. Please help. Thank you.
Honestly, I don't have experience with anything that size, so I can't offer much. Also, the type of steel has a pretty big impact. Since not many other people post here, you likely won't run into someone that has a good answer here. But this site: http://www.thehurl.org/tiki-view_forum.php?forumId=1 will provide some good feedback I'm sure.
Good luck!
