Photon713 (guest) 1257113086|%e %b %Y, %H:%M %Z|agohover
Thank You, Craig…great idea. I've only used that stuff for trolling for Blue Fish. Will have to check it out….
Craig Macomber 1257100618|%e %b %Y, %H:%M %Z|agohover
Thats in interesting project. Personally I would recommend using surgical tubing (latex tubing) as a spring (The same stuff used in slingshots usually). A lot of hardware stores sell it, and it is far easier to adjust than springs: you can just add more, or adjust the tension in it. The main issue with the stuff is that it does age and degrade over time, probably more than a spring.
Photon713 1257095787|%e %b %Y, %H:%M %Z|agohover
Good Afternoon, all…
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.
Craig Macomber 1256600606|%e %b %Y, %H:%M %Z|agohover
Ballisa scale fine. I have one about that size. It shoots arrows 100 yards roughly. I would recommend starting with an onager. They are really much easier to make, and better at throwing projectile than ballista (which are a pain to make throw stuff other than arrows. I never got mine to work with non arrow projectiles). Onagers are much easier than ballista anyway, and work on the same torsion principal. If you get one to work, you might then progress to a ballista, but learning about torsion first on an onager will save you having to fix every mistake twice (as ballista have 2 bundles). Also, an onager could easily meet your requirements, so if it takes too long, you could just use it. I have an onager much smaller than that which has thrown gold balls over 200 yards (600 feet!). A ballista would probably be more accurate though.
Be sure to check out the torsion section.
fantom (guest) 1256524918|%e %b %Y, %H:%M %Z|agohover
I have a project to design and build a torsion engine device to hurl a marshmallow (7 grams) to hit a target 30 feet away accurately and repeatable. The device must fit in a meter square "box". I was thinking that a ballista would be the most accurate device. Unfortunately, all the information I have been able to find are for much larger or smaller devices. Any guidance would be appreciated on the scalability of these devices.
Thanks!
King of Halves 1251451432|%e %b %Y, %H:%M %Z|agohover
Sorry it's taken me so long to get back to this. I think I've gotten most of the information I need. It'll probably take me a few weeks to put it all together and I'll undoubtedly have a few more questions as I go along.
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
Craig Macomber 1251006546|%e %b %Y, %H:%M %Z|agohover
Well, potentially, half the energy goes into up (for a 45 degree throw), and half into forward. So, thats a 50:1 mass ratio, so 25 times the CW drop into vertical, thats about 150 feet*25=3750 feet up. I don't remember the equation for range from vertical height, but its much more than double, so 8000+ feet with the 25 ton projectile. 50:1 is a mid/low mass ratio, so efficiency around .4 might be possible. Thats 3200+ feet, and you probably lose at least 500-1000 more to drag, so I would think I had it about right. You could opt for double the counterweight (or half the projectile weight), and around 2/3 the arm length and get about the same results (The efficiency would be lower, which is why about 2/3 instead of half the arm length)
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!
King of Halves 1251003714|%e %b %Y, %H:%M %Z|agohover
I found this handy page for doing calculations
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)
King of Halves 1251003191|%e %b %Y, %H:%M %Z|agohover
Thank you!
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…
Craig Macomber 1251000162|%e %b %Y, %H:%M %Z|agohover
Flaming wood has some issues at massive speeds (it is not dense, so lots of drag, also the wind could put out the fire). Thus I would tend to favor throwing more/larger projectiles. A mixture of sizes thrown at once would produce good scatter (the smaller things have more surface area for the volume, thus more drag and less range). Because of the massive drag and impressive release height, rather low angled throws would be best (10-15 degrees maybe.) I don't know how much the proposed arm would weigh, but it would be reasonable to throw something of roughly equal weight (max, assuming a light arm), or less, with maybe 50 times that weight in counterweight. The majority of its range will be lost to drag, so you could throw twice as much stuff almost the same distance.
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
King of Halves 1250991885|%e %b %Y, %H:%M %Z|agohover
Well, this thing is essentially for besieging a forest. Think classic fantasy orcs-vs-elves. The orcs have all the manpower in the world but can't actually enter the forest (magical compulsion) so they are burning it. The forest is enormous. It was modeled loosely after pre-westward expansion United States, so the forest itself runs north-south for over 2000 miles and east-west for about 800. The orcs have been burning it steadily for about a decade. There's about 65 million acres on fire in the current era of the game world. The elves are extremely good at keeping the fire from spreading rapidly, but it's a losing battle. Every time a few more feet gets reduced to ash the orcs can move their seige weapons up a little farther and hurl deeper into the woods. The burnt husks of the trees on the outside of the blaze get chopped down to size, soaked in oil and used as ammo.
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
Craig Macomber 1250927343|%e %b %Y, %H:%M %Z|agohover
14th century craftsmen could not make a floating axle treb on that scale I don't think. Making the wheel assemblies basically requires rail road level steel working. If you want to go in that direction, I recommend what I saw one college team did with their floating axle, it slid on the tracks. You could include rollers to reduce friction. However, given large scale light wood, they could make a treb basically identical to Trebarbaric where the frame rolls across the ground quite a lot when throwing (That thing is so amazing to see in person!), except 10 times bigger. Having the frame move instead of the axle is not only much easier and more realistic, but you gotta admit having a frame that size roll around is freaking cool. The frame moving has basically the same benefits of the axle doing so. Check out my videos of it.
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.
King of Halves 1250917594|%e %b %Y, %H:%M %Z|agohover
Hi folks,
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
Craig Macomber 1243462334|%e %b %Y, %H:%M %Z|agohover
Thanks!
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 :)
Mr Roogle 1243418491|%e %b %Y, %H:%M %Z|agohover
Hi there, this is a more general question about your great looking site? I'm only relatively new to wikidot and i was wondering how you added the picture in the top bar and the gradient trasparency down the left hand side? Any tips or advice would be great. Even if you just pointed me in the right direction…I would love to see the coding i just don't know where to look.
Cheers,
Ruben
Craig Macomber 1243190909|%e %b %Y, %H:%M %Z|agohover
Craig Macomber, 1243190909|%e %b %Y, %H:%M %Z|agohover
alan (guest) 1243185037|%e %b %Y, %H:%M %Z|agohover
What is the best kind of trebuchet to build if it must fit into a 2x1x1 meter box? Something simple is also preferable. Thanks!
alan (guest), 1243185037|%e %b %Y, %H:%M %Z|agohover
Craig Macomber 1243114672|%e %b %Y, %H:%M %Z|agohover
It could possibly be some sort of axle, possibly the axle for a hinged counterweight, or maybe even the main axle, or some other axle.
Craig Macomber 1242625723|%e %b %Y, %H:%M %Z|agohover
I would recommend something simple, but doing a good job of it. FAKAs, FATs and other complex types offer lots more range when compared to arm length (but require a larger machine for a give arm length. Even for the same machine size they will throw further though). Those complex types also have a tendency to fail completely or not work anywhere near their potential. A carefully built HCW or Wheel treb would be my recommendation. Make a solid frame and axle (it can be ugly and heavy, as long as it holds the axle up), then focus of the arm and tuning. The long arm should be very light and tapered, and thesling should be very light as well (just needs to be strong enough to not break. You could make it out of dental floss and duct tape). If you get that done well and early, you should have time to tune the sling length and pin angle. If you get that done well and early, you could use what you learned to build a second arm for the machine (but keep the first) that could be something more complex if you want (like a wheel treb, whipper, KA, etc).
Craig Macomber, 1242625723|%e %b %Y, %H:%M %Z|agohover
Morgan (guest) 1242433744|%e %b %Y, %H:%M %Z|agohover
I don’t no what type of trebuchet would get my group the furthest but without to many problems, we are an advanced construction class so we'd like a challenge but it cant be overly complicated, the size would have to be around a meter and a tennis ball would have to be the ammunition. Please give me some advice on a design that would suit me best. We dont want any plans but tips and ideas would be greatly apreciated Thank you.
Morgan (guest), 1242433744|%e %b %Y, %H:%M %Z|agohover
