Trebuchet

admin

I'm supposed to create a trebuchet for Pre-Advanced Placement Physics.  I'd love to make it out of something other than the stereotypical wood and weld mine together.  I'm really new to the welding game, so could any of you guys help me out with the design of it?
Reply:Are there any requirements or goals that are supposed to be met by the trebuchet? Do you roughly know how big you'd like to make it? What are you going to be throwing, something small like marbles or big like cars? Give us some input so we can give you some.
Reply:They are not that difficult to do. Basically you have an arm on a pivot on supports. The pivot is positioned on  so that one side of the arm is longer than the other. On the short side you have a weight. Some units use weights that arm attached to the arm sort of like a stack of washers on a bolt. Another style uses a swinging "basket" that holds the weight. On the long end is a rod and one end of the sling slips over the arm. As the arm swings up the sling will slip off the end of the rod throwing the projectile. By bending the rod you can adjust when the missile is released. The release is usually some sort of pull pin, but you can get fancy if you want. The larger and heavier the more complex the release will need to be to get a smooth release.If I was doing this as a project, I would make the pivot on the arm adjustable, that way you can show what happens when the arm pivot is long or balanced. I would also set it up so that the counter weight is adjustable. Either add or subtract "washers" or add more weights to the basket.Discovery or the History Chanel had a great show where they built full sized units of each type and tested them. I'll see if I can find a link..No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:Link I found real quick thats got a decent drawing that might help.http://science.discovery.com/tv/punk...trebuchet.html.No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:some of the smaller ones ive seen used 4x4 and 6x6 for the frame. the big ones ive seen use 12" posts and build the mounting brackets out of 3/8" plate. those are normally the ones that can throw small cars.I break things for a living...
Reply:A great deal of the success of the trebuchet was it's memory.  IE..... the memory of the wood.  It could sling a boulder a very long distance due to the whipping effect of the wooden mast in combination with unrestrained movement of the carriage.The flex in the wooden mast was crucial.Remember that wood has a great deal more memory than a steel member.A wooden bridge, properly designed, will withstand many more load cycles than a steel or concrete one."Any day above ground is a good day"http://www.farmersamm.com/
Reply:Originally Posted by farmersammA great deal of the success of the trebuchet was it's memory.  IE..... the memory of the wood.  It could sling a boulder a very long distance due to the whipping effect of the wooden mast in combination with unrestrained movement of the carriage.The flex in the wooden mast was crucial.Remember that wood has a great deal more memory than a steel member.A wooden bridge, properly designed, will withstand many more load cycles than a steel or concrete one.
Reply:Originally Posted by BlazeS70True...would a metal frame and wooden arm be a good combination?
Reply:Originally Posted by sn0border88Your the one trying for AP physics, shouldnt you be figuring this out?If you want advice on how to weld on together its one thing, but this is like getting someone else to do your homework.
Reply:I think there have been quite a few threads about these French 'thing flingers'. right on up to flinging cows if I remember correctly.Here's one little one.http://weldingweb.com/vbb/showthread.php...ight=trebuchet
Reply:Originally Posted by wannabe_welderUsually part of the design process is finding options for the most practical design.  You're not building the kids project for him, just giving him pointers that might help him decide on the path for his project.  If someone offers information and the kid asks a question in response, what's the problem with that?
Reply:Originally Posted by wannabe_welderUsually part of the design process is finding options for the most practical design.  You're not building the kids project for him, just giving him pointers that might help him decide on the path for his project.  If someone offers information and the kid asks a question in response, what's the problem with that?
Reply:They make trebuchets out of steel, they're called artillery. Steel would take away from the mystique of the machine. Besides novice welding and machine that hurls things is always bad idea. From what I've looked at most modern reproductions use wooden construction with steel hardware and reinforcing strapes at joints. Personally i think the trebuchet has been done to death. I think a ballista would be a more challenging project for physics students. But I dropped all the AP classes my senior year so what do I know.Ranger 250 GXTSmith Gas Axe
Reply:Originally Posted by BlazeS70You're right, but I guess I should've been more clear about what I was asking for.  I know it needs a base, arm, sling, and a counterweight...and it's obvious what the general trebuchet design looks like.  But how would you go about *welding* it?  Like, what would you do so that the arm can pivot instead of sit there welded to the frame?
Reply:Originally Posted by sn0border88I already know this is going nowhere, but I would think for a physics class he is asking questions that he would be much better off actually doing the research and figuring out why instead of asking random people on the internet. Its not like trebuchets are hard to research or something.
Reply:How big do you want it?I build a bunch of these little guys each year for teachers in a workshop I help out with. I have a class set of 15 for my 8th graders. Not metal but cheap and fast to make. It launches rocks - nuts and bolts what ever is handy. We fling projectiles at bucket with Osama Bin Lauden on it.The arm should have a 4:1 ratio: The section holding the projectile should be 4 times longer than the counter weight portion. The frame on the little guy is 15” tall.If you want more info e-mail me and I can send more info.My advice would be to build a class set of frames and let the students figure out The BEST (length of arm – wheels vs. no wheels – fixed or hanging counter weight.A great DVD is called Medieval Siege by Nova http://www.pbs.org/wgbh/nova/lostempires/trebuchet/Check out the links some are very goodThe math teacher across the hall want to build some for her class. I plan to make these out of metal and wood so I can collapse them to lay flat (storage space is at a premium for me.) It will be a few weeks before I start to build but I will post my plans when I get to it.Dave ReberWadsworth Ohio
Reply:I forgot to attach pictures: Attached ImagesDave ReberWadsworth Ohio
Reply:Reebs, that's the link I was looking for last night. It was Nova, not the discovery/history channel like I thought! Very good show!.No government ever voluntarily reduces itself in size. Government programs, once launched, never disappear. Actually, a government bureau is the nearest thing to eternal life we'll ever see on this earth! Ronald Reagan
Reply:I have shown that dvd (or parts) to young and old alike it is always a hit. A few years ago my daughter was sick so I handed the dvd to the sub. (one who has no class control) and my worst class of unhung murders was walking in the door. The class was perfect they loved it.Dave ReberWadsworth Ohio
Reply:In the alternative, ya could carry the rock, and drop on the opposing dude's headWAtch out for the boiling oil, crossbows, and such,  and keep yer feet dry when crossing the moat"Any day above ground is a good day"http://www.farmersamm.com/
Reply:Our university recently held a miniature Punkin' Chunkin' competition which brought out several student machines including a modified catapult, a leaf spring ballista, and a couple trebuchets. We had decided to build a trebuchet borrowing from the King Arthur design instead of the typical fixed or hinged counterweight designs. The following site was more than helpful.http://thehurl.wikidot.com/trebuchet...king-arthur-kaIt was chosen due to the fact that only a fraction of the counterweight is neededto provide the same projectile flight. The tuning lies in the trigger and how the weight released as well as sling design. Our launcher is about a minute into the video.The main arm is 1.25" MS tubing and .125" MS plate, all TIG welded. It utilizes approx. 95 lbs of counterweight.The overall length of the arm is approx. 8' with counterweight in trigger position.Good luck.Last edited by CRAZYTasty; 11-09-2009 at 08:24 PM.Lincoln Pro MIG 135Lincoln Precision TIG 225
Reply:Looks like a lot of fun, I need to organize something like this at my university and see what people bring out
Reply:If you go over to instructables.com and search for trebuchet, there's one easily made from the rear triangle of a bicycle frame and a 2x4.  Kinda cool, looking at building it myself .....
Reply:This one is slick.City of L.A. Structural; Manual & Semi-Automatic;"Surely there is a mine for silver, and a place where gold is refined. Iron is taken from the earth, and copper is smelted from ore."Job 28:1,2Lincoln, Miller, Victor & ISV BibleDanny
Reply:I made a prototype this weekend. I'm real happy with the way it turned out. It is 23 inches tall and used a 20 pound counter weight. It launched a golf ball over 100 feet (it has a bunch more in it). I will post pictures this weekendDave ReberWadsworth Ohio