I am hoping that this forum can best answer a question from a newbie. It's a bit unusual. I am designing professional pitching horseshoes and want to create a piece of equipment that will test launch each design as if it were pitched by an individual between 27 and 30 feet. I have been experimenting a bit with moving around the center of gravity of the designed horseshoes by adding and subtracting weight from various locations around the perimeter of the horseshoe. I want to be able to create a device that would simulate a person pitching the horseshoe underhanded. It seems that my simplest solution would involve a spring of strength necessary to pitch the shoe with a trigger release at the appropriate location.

I need to buy the necessary spring, but, don't know how to calculate the strength necessary and convey the request to a spring company. I would assume a launch angle between 30 and 45 degrees. Weight: 2-1/2 pounds. Release point: About 3 feet above the ground. Any help appreciated.

Be sure to check out the torsion section.

Thanks!

Thank you so much for your help and expertise. I'll link you the finished product once it's done. (might take a while. Lots of revisions and play testing to go through.)

- Jasper

That page is confusing. I have no idea what it is doing. It has no way of getting the true counterweight drop (No axle height involved). I have absolutely no clue that that page is trying to do, or how.

If you want to assume the arm is denser, you can just assume it is stronger for its size and make it skinner so it still weights about the same :)

Average wood seems to be around 500 kg for cubic meter, so thats half a ton, so 50 cubic meters makes 25 tons. Cube root of 50 is about 3.7, so about 3.7 meters on a side cube, or maybe a 4.5 meter diameter sphere of loosely packed chunks.

If you want to scale the masses, just multiply the counterweight, projectile and arm mass by the same value and the range will stay the same.

Generally long levers can be used instead of a chain of triggers. I don't think I have a good picture of trebarbaric's trigger, but it is quite simple, and just have about 1 foot levers. Generally the arm is drawn down, the trigger is set (using a different line attached to the arm) and the draw down line is removed. The forces on the trigger are actually pretty small in comparison to the other parts. You are probably only dealing with around a 100 ton load on the trigger, assuming it is properly perpendicular to the arm, and attached near the tip. You can actually buy a trigger on that scale: http://www.seacatch.com/models.htm though there are much simpler designs that scale pretty well. A trigger under such loads often has issues with wear and tear, and can get stuck or break.

Generally, if the trigger line is too hard to pull, you can simply use a single long lever to amplify the force.

If you have any further questions, just let me know. It's and interesting topic!

http://andypsionfan.users.btopenworld.com/trebdrop.html

and when I put in a 25 ton projectile and a 1200 ton counterweight the necessary arm lengths are quite a bit shorter than what we've been talking about. Have I put the numbers in wrong? Admittedly, I know very little about what this program and the variables actually represent (translation: I have no idea what I'm doing)

This is exactly the sort of information I was hoping for. That lead counterweight is actually quite a bit smaller than I'd originally thought it would be, and I like having it be able to be disassembled into smaller pieces for transport. The rope/sling is a part of the design I hadn't given much thought and I'm amazed at how complicated that (what I assumed to be) simple aspect of the design has become.

Icewood is described as having a similar weight and feel to Ashwood, but with a much higher resiliency and tinsel strength. I don't know if that changes your numbers any, but balsa wood seems like it would be too lightweight to accurately model this. The text I'm working from describes Icewood as both "strong, with a perfect combination of flex and rigidity" and as "ideal for building such a massive weapon". That being the case, it's pretty much a blank check to have it have whatever properties would garner the best results.

As for the trigger, the design I had in mind was based on a model for large machinery called an "avalanche trigger" wherein a trigger mechanism that is able to be released by a human sets off a larger trigger that no human could realistically release, and so on, until the sequence culminates in the final, largest mechanism being thrown and setting the device into action. It's a bit complex, and I'm not sure how i'd design it. If you have any ideas that are simpler or easier, I'd love to hear them. I'd prefer to have the draw down line be reusable. (cutting or burning through such a rare and unique component seems like something to avoid)

Now I have to do some math and figure out how much actual space 25 tons of wood takes up…

Lets assume the wood is a dense as balsa wood (170 kg/cubic meter) and the arm is nicely tapered averaging 1 meter in diameter (Size at the axle does not effect things really, so it can be much larger there). That comes to about 54 metric tons of wood in the arm. I think throwing 25 ton loads of burning logs should suffice, so about 1200 tons of counterweight might throw in the 3000 feet area. Swap in a longer sling (in the area of 300 feet instead of maybe a regular 200 foot one) for single lighter dense projectiles (mostly rock and metal), maybe just 1-5 tons for high range (it really just depends on the drag mostly, but it could exceed a mile most likley). Btw, a 1200 ton weight is about 95 cubic meters of lead, or a cube 4.5 meters (15 feet) on a side. You would want to make it in smaller blocks attacked after the machine is assembled so you don't have to lift it all at once. Instead of lead, you could go for a much larger bucket full of scrap rock.

The tensions in the sling ropes will be massive. I can't work them out for you (it would be too much work), but it is probably in the area of 50 times the projectile mass (Thats a totally random guess). For pulling down the arm, you need ropes at least as strong as 1/3 the counterweight, depending on the arm ratio (I would say 4:1 is fine). Who ever has to carry the rope up will most likely have to carry a thinner rope, which would be used to haul up the larger one (Which in turn could pull up an even larger one if needed). It looks like 1 inch steel cable would hold 50 tons or so, and strength goes up with the square of the size (its proportional to the cross-section). Assuming your rope is on par with steel cable, 4 inch diameter sling lines should be reasonable. 2 inch should suffice for pulling the arm down. Such a rope, assuming a density like nylon, would be around 360 kg for a 500 foot length (about how high the arm tip will be). You probably want the axle around 200-250 feet up.

The easy way to trigger such a machine is to simply break the draw down line (burn through it most likely). A real trigger for such a device would be hard to make (but possible, I can offer up some designs if you wish).

I love not having to work about people actually trying to build something using the numbers I provide :)

Oh, if you haven't seen flaming projectile hurled, be sure to check out the various flaming piano hurl videos around. Here is one: http://www.youtube.com/watch?v=-wVADKznOhY

The weapon we're discussing is sort of like the flagship of the orcish fleet of siege weapons. It's as much a symbol of power as it is a weapon, kind of like the Death Star in Star Wars. Its usual payload will be intended to spread fire. Probably oil soaked bundles of logs. If they could get a bead on where the elven command post was they would probably load flaming scattershot (maybe 10-20 pound rocks, as many of them as possible). they tend not to throw bodies because bodies are both food for the orcs and one of their means of making oil. (yeah, it's gruesome) There is always all the waste from these endeavors, and it sounds about right for the orcs to gather it all together and toss one group of really disgusting giant sacks about once a month. Like the largest and most awful water balloons imaginable. (I feel dirty just for writing this…)

As for the sling, I hadn't thought about that. I guess that could explain what they did with all of the branches that were cut of of the trunk. I like it. Thanks for the idea. Assuming that this Icewood rope is about the same strength as modern synthetics, how thick would the sling need to be, how long, and how much would that much rope weigh? As you mentioned, someone is going to have to climb this monster carrying the rope. I need to figure out what kinds of rediculous strength feats that particular baddie needs to be capable of.

Anyway, does that cover what you wanted to know? Any other questions?

Thanks for the prompt reply, btw.

- Jasper

I should note that there was a steel FAT that threw pianos 900 feet with 9 tons of counterweight. They can be made large, but it is much harder to make a large one technologically than a wheeled HCW like trebarbaric. Also, in a FAT, the arm is not the big deal part as it is with most other designs. The FAT's track, vertical stand, and counterweight holder/axle are the issues, not to mention the much higher complexity.

Trebs scale basically linearly, and mass scales independently from size. So 10 times as big means 10 times as far of range. Now, because of air resistance, it would not throw 18,000 feet (thats like 3.4 miles). The main issues preventing such scaling is the availability of a throwing arm for such a machine (to be strong enough, it would be too heavy), and the budget man power and space. Seeing how you have actually addressed every one of these issues, you should be able to keep things quite realistic.

On a technical note, you want a stiff, not flexible arm (The arm flexing just removes energy from the throw).

The specific parameters really depend on its intended use. Trebs were exclusively anti castle weapons designed to slightly out range the archers. Thus they threw 100-300 or so pound stone balls 200-300 yards or so. (Those numbers are just guesses, I haven't studied hurling history really) Any more weight or range was useless.

The pay load could be anything you want. As I said, mass scales independently from size. Also, you can have a counterweight to projectile ratio from about 10:1 to very large (Trebarbaric has 8-10 tons for an 8-10 pound projectile, thats 2000:1). Assuming access to large amounts of Icewood and lead are available, such a machine could, to be true scale with medieval ones, could throw 10 times as far with 1000 times the counterweight and projectile mass. That means 100 tons going 5000 feet, and maybe a 8,000 ton counterweight. That is kinda insane, why would anyone need to do that? It would throw about the same distance with lower masses, say 5 ton projectile and 400 ton counterweight.

One on your scale could be used for shipping (lol), anti personal (lots of lethal sized rolling projectiles), building smashing, corpse chucking (get them with the black plague! That was actually used at least once), fire spreading, or basic scaring the heck out of every one. If you can offer up their reasons for building the device, I should be able to work out some pretty reasonable specs for it. It makes a huge difference what they want to throw. If you just want to throw something huge (say, a 10 ton block) 300 yards, you really have no need to make an arm that long, you just need lots of counterweight. I would say we are looking at a range of about 3000 feet minimum here (assuming dense projectiles), but more or less could be possible depending on what projectiles were chosen based on the intended use.

If you are willing to mess up and kill some people (oops), a machine that size could throw people (the accelerations on large machines are not higher, they just accelerate over a longer time as the counterweight acceleration is fixed to gravity). Being large, it could throw people at 400+ mph a few thousand feet. Paratroopers! Actually a machine that size, if tuned to throw small dense things (100 pound lead balls) and loaded with 50-100 tons of counterweight or so, it would probably have issues due to throwing super sonic.

We are going to have to assume Icewood can be pounded out and woven into ropes to make the sling, because they did not have modern synthetic rope, or high strength steel cable. You have to make the sling and ropes to pull the arm down for cocking out of something.

For construction and proportions, copy trebarbaric. It is a simple and good design. For lifting parts into place, make giant A frames, which get up righted and used like cranes (There is a great nova on trebuchet construction using traditional methods that covers this - some one stuck part of it on youtube, http://www.youtube.com/watch?v=j9lhcjupnzk I think you part part later in the show though)

For reload time, I honestly have no idea. Assuming an easy to setup winching system, and unlimited man power, the thing could be cocked pretty quick (maybe 5 minutes after they get some practice). The loading time depends on the projectile, but would probably take quite a while. Also, getting the winching system setup would require a brave guy to actually climb a good 500+ feet up the thing (probably still swinging a bit!) to attach the draw down lines. Waiting for the machine to stop swinging before reloading would take a long time, and any effort to seriously reduce the time by adding friction would just catch the thing on fire. I would say at least a a minute. Pushing the frame (assuming its a rolling HCW) around would take a while too. Overall, I don't think throwing more that once every 15-30 minutes would be practical, but this is fiction, and 10 min would not be pushing it too much.

So, what what is is going to be used for? Then I can whip up some numbers for you.

My name is Jasper and I'm a role-playing game designer. I've been working on a project involving a fictional war machine of absurd proportions and I wanted some help with the hows and the whys of the concept.

Within the setting of the game i'm working on the Bad Guys have a giant trebuchet that is only briefly described in the existing text. My job is to flesh out how it works, what it's made of and what it is capable of.

Here is what I know-

The main throwing arm is an entire tree. A fictional, super strong and flexible wood called Icewood. Icewood trees grow to impossible proportions (300-500 feet). The tree that makes the main arm of the weapon is 400 feet long. Icewood is described as being lightweight, flexible and remarkably resilient.

The empire that has built the weapon has an effectively unlimited amount of manpower and resources to use in it's construction, but relatively crude technology. Roughly that of 14th century craftsmen. In my mind, this weapon is on the same scale of engineering that built the Pyramids and the Great Wall of China.

So, the question is, if you had effectively unlimited manpower and resources, 14th century crafting technology and a nearly perfect 400 foot main arm, how would you build this weapon and what could it do?

What would it's dimensions be?

What materials would you use to construct it?

How heavy should/would the counterweight be?

How heavy/large could the payload be?

How far could it hurl?

How long would it take to reset and reload?

I'd like to use a Floating Arm Treb for the design, even though it isn't historically accurate (it's fantasy after all), but I don't know if the sheer scale of it would make that design tear itself apart when it fires. (the track-and-wheel system seems vulnerable to scale issues, but I'm by no means an expert.) If the FAT wouldn't work, that's fine. The above questions still stand.

Thanks for the help!

- Jasper

The appearance is all done through a custom theme. The side bar trick has no transparency. It is just a image that transitions to gray carefully placed to line up with the other header image. I should note that my top bar image was carefully made such that it could tile horizontally without obvious seams.

There is some stuff to get you started at: http://community.wikidot.com/howto:design-your-own-css-theme

My CSS is at http://thehurl.wdfiles.com/local--theme/thehurl4/style.css though it is quite a mess :)

the hillfort isnt realy big

http://piliakalniai.lt/piliakalnis.php?piliakalnis_id=573
it was in area of heavy fights with Teutonic Order during 14th century

coud it be part of hinged counterweight or any moving part?

If you have information about size or materials I might be able to come up with something, but it is unlikely.

image

http://forum.istorija.net/forums/thread-view.asp?tid=3931&mid=61246#M61246

Thanks!

Just some quick specs…

The competition requires throwing a gallon milk jug full of water (8.35lbs) 45-60 yards. Trebuchets only, no catapults. Scores are based off of how close we are to hitting a "castle wall". Our actual competition is this weekend.
We built a HCW trebuchet out of 2x4's and 2x6's and are using 300-400lbs of counterweight.

Thank you for your time and resources….
~Levi

If you wish to compete in the event email moc.rr.wen|sinedtapts#moc.rr.wen|sinedtapts

First, I have no plans. Second, if I did, I probably wouldn't give the out anyway. It is much for beneficial for people to make their own plans rather than buy wood shaped like the particular scraps I used (it was made fully from scrap other than the wheels and rails.) Knowing how it should work will allow you to make your own plans, and will leave you in a position to understand and fix problems. I will consider extending the details on the page to cover construction and design aspects though, as that could be very useful. My idea of a plan is a 3 foot track 3 feet of the ground with a FAKA arm on it. Thats about as much detail as I see being appropriate other than design tips (which are probably what you need anyway).

You made the right choice to build a small one first! The trigger is the hardest part by far, so having trouble with it is expected. If you can specify what aspect of triggering you are having trouble with (understanding how/why it works, building the primary or secondary, etc.) I can help you with those issues. Making a K'nex secondary is a horrible pain by the way, so if that's your issue, I can offer pictures of mine and some advice, but it's hard to make work.

Thanks again,
Craig

Conor

First you need to figure out the things you can adjust (I suggest sling length, pin angle and secondary trigger timing), and determine the effects of them. Then determine whats wrong with your machine and choose adjustments to fix it.

Read tuning and the details on floating-axle-king-arthur.

Is there a template or something for that? I little sliver of information about arm to counterweight lenghts, where to drill the holes, etc? :)

I would pay you in pirate gold (assuming I ever get some)

I have also been trying to make popular pages more user friendly for people new to hurling. Generally this means linking simpler content, having some background text, and providing videos.

I also intend to expand to cover more topics. Things like kits, materials, more basic simplified tuning information, longer machine type descriptions. I might even make a section for sling shots, spoonapults, and other odd designs.

I ask you this, where do you intend to put the energy? I suggest the projectile, but heat and broken parts are also acceptable. Have you ever keep a car engine floored with the clutch out? Tried to kick something and miss and fall down? If you try to put energy somewhere, and fail, it will go somewhere else, and considering it did not go where intended, it will go where unintended. Even if your tuning is simply imperfect, it will be violent. FAKAs are one of the hardest most complex designs to make work properly. If you don't work through the physics a bit, you won't be able to operate it. You are experiencing the "Disadvantages of the FAKA" paragraph, except you are misfiring intentionally, known as dry firing, something you should never do.

As far as the axle smashing into the front of the frame, may I suggest adjusting the horizontal momentum on the arm assembly to be less forward? There are instructions on the FAKA page.

I'll try to add some basic debugging instructions to the page as this is a exact copy of what happened to another guy.

Basically, I built a copy (sorry, its too cool!) of your Golf Ball Beast over the past three weeks. I have the frame done, but one major setback I am having is the throwing end. I have an arm, the counterweight arm, primary and secondary triggers, but i can never get the arm to stop its forward motion after it has flung. I'm hoping it will be as simple as adding a projectile, but I don't know. I guess I am just horrible at tuning.

My tuning method thus far has been to rotate between the holes I have drilled in the arm and the counterweight arm, trying to get that perfect combination, but to no avail. Any tips and or pointers?

Thanks!

Having a projectile will drastically all of the mechanics. The whole point of the machine is to put energy into the projectile. Not having one is like flooring the gas in your car with the clutch in. No where for the energy to go, so stuff gets abused. On small machines this is not so much of an issue (durability is higher for small things for several reasons), but many larger machines have been broken by firing without a projectile, or simply by using one thats the wrong weight. Trust me one this, if your machine will be efficient at all, the projectile and sling will change the tuning completely. Like I said, my only throw without a projectile ended like yours, hitting the end of the frame and derailing, while I have only hit the end on 1 or 2 throws with projectiles, and that was directly caused by an early secondary trigger release. (Tuning can be confusing!)

As far as sling length goes, make it adjustable as you will want to fine tune it. My slings page has details, but I need to update it.

is me btw =P

J-Buchet, and a few other trebs have made a great improvement to my design, and added a top rail to prevent derailing. Looks like your machine can survive them ok, and it only seems to derail after it should have released, so it should not be too much on an issue.

I'm surprised how fast the design is spreading, but I guess thats what the internet does! I seem to find a new one every day! I need to update the page with more info.

http://www.youtube.com/watch?v=7UNmxO_l2ig

http://www.youtube.com/watch?v=9jyINsWxvqk

I have some ideas to help; I'm pretty sure I can get at least half of the energy by modifying some parts, though I will likely have to remake the complex trigger mechanism.

For now, I'm going to fix the few issues (slipping knots and such) then go throw some stuff. In the bright side, this machine could dry fire safely loaded with 50 pounds. A miss fire where the sling actually deploys could be an issue though.

As I have progressed with this implementation of the design, I have realized several flaws in my machine that should be changed for future ones. Changes can be made to tolerate elastic parts better at the cost of arm drag for example that would be good for a flimsy machine like mine, and least until I get some less stretchy string. Also, before the CW detaches, the transfer of energy may not be as complete as I want because of the same stretchy string and some minor building errors/choices. Again, the next one will be better in this respect.

I'm quite worried about the sling. With the axle around 3.5 feet off the ground, and a 4 foot sling, things could get ugly. 7 feet of string slapping the ground/treb! Also, the tuning literally chooses the release angle, though the first throw will basically be at a random angle, and the next one should fix it, but a random angle on such a machine is bad as it might just slam the sling and projectile into the ground!

The CW came out more compact than I thought, so it should hole a few extra 5 pound disks if desired, but I will have to modify it to work with my planned initial test weight (5 or less pounds) because the CW arm would not properly clear the arm assembly if I simply make it skinner when I remove weights as planned. Also, the primary trigger needs to be designed, but it should be trivial.

I also gathered the remaining parts of the frame, though I still need to locate some hardware and such. I'm really looking forward to getting this thing tested, though I will have to start with just a few pounds of CW so wont out throw my local park. Looks like the treb might actually work!

Now, I think it will work. I always can confidence in the concept, but my implementation of it has left me wondering it it would actually work. Maybe as soon as next week I will be able to get some real throws off.

Thanks.

Cool! Today we started building the trebuchet, but the model is definately scaled down. I have a question about the formula for mass ratio and beam ratio concerning Phssthpok's Rule ( MR = 20*BR)

Can we use that equation to determine the arm ratio for the FAKA? (1.5k/4g = 20 * BR) or is the FAKA's arm ratio fixed?

I assume you mean 1.5 kg/40g. Anyway, you are looking at a mass ratio a tiny bit higher than K'nex FAKA, and much lower than GBB's max. GBB's 1:4 arm ratio seems to work through a very wide range, 50:1 to 150:1. I would recommend something between 3:1 and 4:1. Maybe 3.7 or so, but really with an FAKA, it does not need to be too precise. I'm guessing that anywhere from about 2:1 to 5:1 would actually work well.

Can we use that equation to determine the arm ratio for the FAKA? (1.5kg/40g = 20 * BR) or is the FAKA's arm ratio fixed?

Based on the rules, I think you will have to consider the whole hanger as the CW, so take that into account. A FET is the same as an FAT without the vertical CW guides. To keep the axle from derailing, you need some rollers like on an FAKA.

Because you seem to have some experience with F-series trebs, you can probably just go straight for the FAKA.

Good luck! I'm glad my site has been of some use.