Trebuchet CATAPULT Project/Worklog Updated 12/12/06 Please COMMENT

I am planning to build a trebuchet that is capable of launching projectiles around 10 pounds the length of a football field or more. Heavier objects can be launched if wanted but significantly less range. Copy Machine sailing thru air?

Well basically I am just asking for any advice. Currently I have at least 800 pounds worth of lead stage weights available to me. I am trying to find an arbor so I don't have to build a box to hold that much weight and they are designed for it.

Ok also I am planning the axel to be 7 feet and and 9 inches high. Due to available wood. To hold up the approx 1 ton throwing arm (approx weight when loaded 1ton = 1000 pounds) I am using a total of six seven by ones. That means 7 inches wide and 1 inch thick. Or 7 by 3 since they will be bound together.

These pieces of wood will be vertical to the ground and bear the grunt of the weight. Then I have 8 pieces of the same wood angled at 45 degrees to the ground to support it from falling foward or backwards. Then for left and right I got 2 well built triangles that are 32 inches high and 38 inches wide.

Um lets see I just need to ask your help since you guys are all extensivly capable of building things and know tools and materials the best. How thick an axel I might want to hold up a 1 ton object? Can I get bearings for an axel which should be at least a couple inches in diameter like 3 but I might be wrong which can support over a ton of stress? If anybody knows where to get an arbor the ones used on the fly system in stages?

Also the fun part I need ideas of what to throw. AND A NAME for the to be born beheamouth. So far for thowing ideas I got 8 pound bowling ball fruit like watermelons and cantalope and pumpkins. Also I am going to throw one of the cpr dummies. The baby version of coarse cause a full size would be too heavy. Also I plan if I can find a crappy computer monitor but I don't know the weight of smaller ones. I also wonder if you guys have any ideas for targets since trebuchets are highly accurate if done right? Any other ideas?

I will have a drawing latter on but its basically a Trebuchet just a little moddified for safety and stability. I just need some help and advice I hope I posted this in the right section.

 

Em, I thought 1 ton = 2000lbs?

I have no idea what kind of axle or bearings you would need.

As for targets- old cars. Maybe prop up some plywood sheets and paint on a target.

L J

 

interesting

why not try a thick steel axel with various ball bearings to distribute the weight like truck ball bearings they certainly can wistand 1 ton, .

try to make the arm flexible like a fishing rod in the last part of it like in the middle forward, this way it can work almost like a sling shot.

for the part that contains the projectile use a.....cr*p... forgot the name in english...here we call it a "funda", remember the bible, david vs goliath? the weapon that david used to toss the stone to the giants skull?

as for a target, use your imagination

 

yeah a sling is what its called. That is used in this design. Old Cars lol that would be awsome. I wonder where I can get some that would be awsome to see what happens to it with a bowling ball hitting it on the roof. Hmmm truck bearings I wonder you think just regular car bearings would work. Does anybody know anything about cars? and the bearings. And what kind of diameters they use.

 

http://www.algobeautytreb.com/trebmath35.pdf

a good read if you are serious about this.

gets a lil too im depth for my taste, but its all there

 

oh man your right sorry I idiot. Ok half a ton. But the whole structure without the arm I calculated to be around 560 pounds with the wood I am using. But I am probally low. Plus the cw and arm it will get close to 2000. Thanks for the correction man. My mistake.

 

Cool idea. If it works out let us know. I would love to be able to launce a sony computer or something like that. Maybe a large ball of dirty laundry soaked in gasoline and a match.

 

Is it alright if I ask you what your age/educational background is?

Also, do you plan for this to be stationary or mobile? If you don't have a strong background in physics, brush up on particle physics and kinematics. The last thing you want to do is underestimate the range and have a bowling ball (or whatever else it is) fly into traffic.

 

I have never done this, but just thinking about it right now. I would build it out of steel pipes.. they are heavier, but it is alot easier to weld steel then to connect wood to withstand alot of stress.

For the axle, I would use two front wheel axle's of a RWD car. I would weld the rims toghether and weld the car-part to the rest to the steady part. Then you can drill holes in the double-rim and weld anything you want on that. Those axle's can hold alot of weight and stress and are perfect for this.

Good luck and be carefull/safe. L

 

Erm, is it legal to build an 8 foot half ton wooden machine of flingy death in one's back yard?

 

As long as they don't find out

But being serious I don't know

 

Actually, I think wood could be slightly better as it is less dense than steel and hence would swing around a little quicker (lower mass = lower rotational moment of inertia). BUT it would have to be laminated. But... that would require a few tools to cut the wood in order to attach them in layers.

In high school, we took a tech course where one of the projects was to take a single 2x4 and machine it such that it was stronger than a standard 2x4. For the standard, we used the best qulity looking 2x4. I don't quite remember how much load it took, but we surpassed it .

Anyways, even if use the available wood (you mentioned 7x1s), LAMINATE THEM! Get some wood glue, some heavy duty wood screws, and spend the money to get some good clamps.

I just saw the link posted above. I skimmed through part of it, and I have to admit... it's a good read, but the modeling is a bit too complex.

 

I know steel is more dense, hence more heavy then the wood. But I just think it's alot easier to work with. Especially if you use steel rims with the car-axle for the center, it's easy to drill a hole, just insert a pipe and weld it shut. But I do reckon most of the trebuchets I've seen are made out of wood.

PS: how are they 'powered' anyway?

 

They are powered by gravity "Gravity Inside"

A trebuchet is the "FX60 with 7900GTX in SLI" of catapults... They were used to swing cows through the air...

 

Lovah - Perhaps the structure should be constructed with wood sandwiched between metal brackets for extra rigidity, that way we're both right!

I'm not sure what you mean by asking how it's powered.

OH NO! Now I want one too! Well, a much more miniaturized one, but still!

 

Hey guys thanks for the suggestions. I am currently an AP Physics student in 11th grade. I am 17. I have built a smaller model already actually in a tech class.

I am not using metal I would like too cause it would be more expensive since the wood I already got it (wood from the stage productions our stage is getting torn down so I get a lot of free good wood). Also I don't have welding torches available to me. This is a school project so yeah legal and I am using our football field. If it goes over no worries since there is enough room for another football field cause there is undeveloped land beyond the football field. Then woods with nobody in it.

I was wondering about the laminating can you elaborate? I thought laminating just to protect wood long term does that actually make it stronger?

Oh by the way most of this going to be put together with bolts. In my expierience screws and nails don't do the job on bigger scale and usually cause more problems. Bolts easier to work with so yeah no screws for me.

Any other ideas for names? I plan on engraving a name on the arm with a dremel so yeah IDEAS PLEASE. Or else the gsa will make me turn it into a gay rights event. And please don't let that happen..... Stupid principle .....

Well the arm is what I am worried about. I am not using metal cause of weight. Currently I got a friend talking to an architect for me about what size wood I should use. So I will tell you the results on that. He also might get me more free wood . HURRAY FOR FREE STUFF

If you want one you can buy one. www.trebuchet.com sells desktop models. I made my own but its pretty cool.

Thanks for all the suggestions I really appreciate it. I will be making this into a worklog too as I build this thing with my AP Physics class. We are getting started after AP tests right now just designing and getting stuff together. So yeah pictures and stuff will be here by May 7th aka the day after our ap. I will get a diagram of it latter when I find a scanner. But it will be here .

 

Ok. Well, you know what plywood is, right? That's what I mean by laminating. I think maybe two 2x4s would offer decent lateral strength, and good strength along the direction where the most stress would be (parallel to the direction of projectile motion).

You need access to a bandsaw. You will not be able to get straight enough cuts with a handheld saw, or at least I don't think so. If you do not have access to a bandsaw (check with your schools wood/tech shop) then they might cut the wood at the place you're buying the wood at. If you can't get pieces cut, no biggie, just buy pannels and assemble them yourself.

Laminating wood is basically attaching layers of wood together. Since you have variety in the grain, there is much greater structural strangth perpendicular to the layers. In the class where we did the project, me and my partner one. We proved that our design would out-perform a standard 2x4. I don't remember if we made it into a I-beam beam or a rectangular one. But anyways, so we constructed a breaking apparatus where we used student's weight to break the beam, and it took most of the class to provide the 1300 or so pounds needed to break the beam. While many of the other teams' beams cracked and broke, ours ripped apart cleanly and featured a pretty cool pattern.

You may want to use wooden pegs to connect laters, as well as bolts if you so desire. But use some wood glue (elmers is great stuff) to hold several panels together. I'd also suggest bracing the wood with aluminum or steel extrusions just because you can never have too much stability.

I'm really interested in this. Keep us updated, and if you start a worklog, post a link here!!

Also, if you need any help with any of the physics, let me know. And you didn't mention if this was to be mobile or stationary. AND in terms of wood... I'd go with a harder wood, but working with it will be a pain. Maybe they have plywood in small enough sections?

 

hmmmm Thanks man I don't know the type of wood I got currently but it is some kind of hardwood. Don't know what but its definitly good stuff not crappy **** like pine or something. Hence why I want to use bolts also. Um its going to be stationary but I do have to transport it to the field that is another reason I am using bolts. So that I can transport in pieces then assemble on the field.

Ok I get the laminating now I got access to a band saw. I am basically doing that by putting the 3 7 by 1's together. If I understand correctly. And worklog wise just to make it simple I will just do it here. Just wondering with your beam how long was it? Cause my throwing arm has to be at least 14 ft which is pretty long and has to be able to not break under at least 1000 pounds of stress.

Also wondering you seem very knowlegable I got these stage weights and I found arbor's which is what they were inteded for but they cost 300 dollars each so that is out of the question. Do you think 1/4 inch plywood attached to some 4 by 4's or maybe planks like the 7 by 1's with screws will be good? Also they will be reinforced by L brackets would you think it would hold alright? The dimensions of the weights is 12.4 inches by 14 inches. It is also 19 inches high with all of them piled on.

 

If you're actually going to build one that size, be careful, the forces involved are immense, and they're a very dangerous item to work with when you start to get them towards firing point.

Have a search around and see if there are any trebuchet enthusiasts nearby to you, as they'll know a hell of a lot more than you about this project.

Other than that, good luck and PICS!

 

Yep pics going up soon as I get started and yeah I know the forces are crazy. Hence why I am looking for advice wherever I can get it. Talking to an architect also so yeah. Firing shouldn't be that big a prob nobody be within a 5-10 foot radius of the treb durring firing so yeah. I built one before and got help from many including you guys . Hurray for making stuff super sized