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madmattd (guest) 05 Mar 2014 18:37
in discussion Other / Other » What happened to

A new forum is now up to fill the void of Come on over to A bunch of the old guard from TheHurl have made the move already.

by madmattd (guest), 05 Mar 2014 18:37

Quite some time ago, Ron Toms (who ran 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

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, 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?

Re: Cal Lab F2k pumpkin hurl by idonahuidonahu, 06 Nov 2013 02:59

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 forums.


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.

Cal Lab F2k pumpkin hurl by idonahuidonahu, 03 Nov 2013 00:01

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: will provide some good feedback I'm sure.

Good luck!

My school is having a contest to throw 1 gallon jugs of water in a few months. I have designed a FAT with about 300lb of counterweight total, but I'm unsure of how large to make the CW axle. The arm is 4.5" wide, and the distance between the vertical supports is 18.5". Each support is 1.5" thick, so from counterweight bucket to counterweight bucket is 21.5", and I was planning on having each bucket about 12" wide. How thick of a steel axle am I going to need so that it doesn't deform after each throw?

Thanks for your help!

I'm glad my tuning article looks comprehensible and useful. Thanks. My newest onager is only 1.5 inches long (Tiny Onager), so its not quite suited for the big chunk. I was at the Burlington Pumpkin Pitch a few times, but I really haven't been doing any hurling in the last couple of years. I just check in in the fall and see what new treb designs are out, and if Chucky has beaten the air cannons yet ;)

Re: excelent work craig by Craig MacomberCraig Macomber, 28 Sep 2012 04:38

chucky 3 has a couple of new things up her sleaves. some safety, some logistics and ease of operation and of course performance. we are realy looking foward to great year of fun comraderie taking down those damn cannons!

chucky 3 ready for 2012 by CHUCKY 3CHUCKY 3, 28 Sep 2012 04:20

this is marc from team chucky.
i dont get on the computer much and just found this site last week while searching for info about torsion bundle pretensioning. your article on tuning was outstanding and would take years off of the leaning curve for both novice and experienced chunkers. sorry about my banters on the other hurl but when i would get alerted by daneboy about some of the posts i would respond with a bit of anger.
how is your machine? i hope things are going well and look foward to seeing you at the chunk.

excelent work craig by CHUCKY 3CHUCKY 3, 28 Sep 2012 04:15

If you use a motor to cock the trebuchet, you have electrical potential->magnetic flux (don't ask me for the details here, I don't know the terms) -> gravitational potential. If you cock it by hand, you are consuming chemical energy to produce gravitational potential energy.

Regarding wheels, sure they effect the energy transfer involved, but they are no more of a form of energy transfer than addling more weight, a longer sling or any other tuning changes.

Personally, I think what happens to the energy after the throw is the most interesting and educational. We all like to teach conservation of energy, but eventually the projectile, and the trebuchet are both at rest, and with less energy than they started with. Where did it go (heat mostly), and why can't you get it back? Thats a real applicable and useful concept! Aside from being a fantastic introduction to entropy, information theory, and thermodynamics, it provides an understanding of efficiency in general, and is widely applicable. The topic of thermal losses in systems is perhaps the most generally applicable transfer of energy in engineering and physics, not a cop-out. In-fact, there is evidence it will be the limiting factor of the universe itself!

Also regarding the frictional and other "small" losses: Most trebuchets lose much more than half of the energy this way, so it is in-fact larger than the transfer to the projectile. And since they are basically the same as the transfer the projectile makes upon impact, (both are thermal) all the energy goes through this transfer eventually. Most of the sound ends up as heat too by the way.

One of my favorite application of this: Where does the energy go when you walk down a hill? (heat!) Since going up hill gets you hotter than down, this proves (after some minimal logic+math) that walking up hill is less than 50% efficient. Neat right?

Its pretty interesting (and quite practical) to compute how much kinetic energy was in the projectile and thus compute the losses/efficiency of the trebuchet. It might be a bit heavy on the algebra, but all the hard parts can be looked up instead of derived. My dad managed to teach me some of the basics of integral calculus doing that exact problem around that age (We derived most of the details ourselves), but I suspect thats not for everyone.

by Craig MacomberCraig Macomber, 19 Apr 2012 05:55
Mal R (guest) 19 Apr 2012 02:59
in discussion Hidden / Per page discussions » Counterweight Stall


My name is Mal and my 13 year old son, Jared, is supposed to be doing a physics project that shows 3 types of energy transfer. He decided to choose to build a Trebuchet Kitset (Pathfinders) and he already knew that it used Gravitational Potential Energy and transferred into Kinetic Energy but the third transfer of energy was a bit more difficult to pin down. He asked his teacher and was told that the third could be the projectile impact causing heat. I think this is a bit of a cop-out as the projectile is not part of the Trebuchet proper. I know there is friction / heat / sound at the fulcrum, sling, pin etc but all these energies are small and not really a full transfer of energy.

Can you please enlighten me on a third transfer of energy within the closed or semi-closed system of a Trebuchet? I was thinking more along the lines of the ‘cocking’ of the Trebuchet prior to firing. I have heard that the wheels on the Trebuchet add 25% more to the firing of the projectile - can this be quantified as an Energy Transfer?

Thanks in advance


by Mal R (guest), 19 Apr 2012 02:59
joe brand (guest) 02 Feb 2012 21:59
in discussion Site Discussions / Questions? » Help please

thanks for the advise so far. there are no real constraints, it has to go as far as possible(3-5lb pumpkin) and be able to be transported by the team to the field, thats really it. I was thinking something with in the size of 4'- 2'x8' maybe a little bigger if the design calls for it. I was planning to do something simple strong frame and towers made from 4"x4" steel hollow square stock. maybe aluminum throwing arm on the sling side and heavier steel on the counter weight side.

by joe brand (guest), 02 Feb 2012 21:59

There is no 'best' design unless you apply some really strict constraints. With no mention of a goal and, no restrictions on parameters other than projectile weight, it basically impossible to choose an optimal design. If you want to throw as far as possible, the ideal design is something that costs millions of dollars to build. If you want to optimize for cost, its free to throw 0 distance. Look at competitions with experienced entrants: there are many different designs they use. If there was a best one, the wold championship pumpkin chuck would not feature more than 6 very different designs.

If you are looking to build something efficient and compact, thats very different from a trebuchet that may take the same amount of work to build, but is simpler and larger with the same range. Until recently (and maybe even currently), the longest ranged trebuchets were just very large HCWs. If you haven't built trebuchets before, a HCW or FCW is a good starting place if you want a design thats not too hard to get right and gets good range for the effort. All the other designs are more complex and mainly efforts to get more range without simply increasing size. I also recommend building a small model first. If that goes well, you can try building models of a few more complex designs if you wish, and scale up which ever you like best.

Most common mistakes I for school project trebuchets: really heavy untapped throwing arms, crummy slings, and axels that are longer then needed (and then end up bending a ton).

Also, "Full Sized". Full sized generally means one of 2 things: medieval scale and can throw 200+ pounds a few hundred yards, or 8-10 pounds competition pumpkins. That said, I mainly work with stuff that fits on my desk.

Anyway, thats what I have to offer. Feel free to browse around the site and ask some more specific questions if you have any. If you want a higher volume of advice, the majority of the hurling community hangs out at TheHurl Message Board. You will get a ton of fantastic advice from those folks!

Re: Help please by Craig MacomberCraig Macomber, 02 Feb 2012 05:09
Help please
joe brand (guest) 02 Feb 2012 04:28
in discussion Site Discussions / Questions? » Help please

I'm a technology teacher on long Island and Im having my Metals two class design and fabricate a full size trebuchet that will be able to throw a 3-5 lb pumpkin. we have a full woods and metals lab, 8 welders, 2 mills, 8 lathes, plasma cutter, etc (all the tooling and raw material needed) there is a competition held on out here where schools compete every october. what design would be best? we will be designing it in Auto Cad. any help would be appreciated

Help please by joe brand (guest), 02 Feb 2012 04:28

Thanks Craig,

Looks good. Hopefully I will have more information about them as my bigger one gets built.


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