Making a Catapult...

demonofaj · Post by **demonofaj** » Sat Mar 03, 2007 9:38 pm

Well, I got most of the frame down, but what I need is some sort of awesome 'force'. By force I mean like the rubber band in a slingshot. I'm not really sure what to use...I was thinking like...bungee cord? I don't want to use rubber bands because it is EXTREMELY brittle (tried it) but not sure I want 'bungee cord' because maybe it will be too much for it's own good. Also, holding it down while pulling back (thinking some epoxy can hold it in well)

Post by **Triton** » Sat Mar 03, 2007 9:49 pm

what size are we talking bout here? i have a trebuchet! its about 7' tall tho and is made of square tube steel, probably a bit bigger than what your talking about

we used a garage door spring to power it but if i get it going again im gonna use a counterweight (200-300 lbs probably)

throwing a 16oz bottle of water 275+ feet is friggen awesome

demonofaj · Post by **demonofaj** » Sat Mar 03, 2007 10:04 pm

DAMN! Well, this is more of a small thing, so I'm saying about the height of your leg...

Post by **Triton** » Sat Mar 03, 2007 10:31 pm

whats it made of? a small bungie cord should do fine and depending on the length of your arm and whatnot you should get decent range too. build the thing as sturdy as you can cause these exert a lot of force in several different ways, stress from pulling the bungie, angular momentum rotational force etc. one of the other teams in the class that we built the catapults in had one that was even more powerful than mine, and about 10x as dangerous, an arm that pulled a garage door spring (normally mebe 2-2.5' long unstretched) to about 12 feet wound up breaking the bottom hook on their spring, it went about 150 feet up and imbedded itsself 6 inches into the ground 127 feet away! that sucker could really launch a bottle tho! 325 foot and we estimated the velocity at above 60mph leaving the sling

its really a miracle that that catapult didnt kill anyone! it was so friggen dangerous to use compaired to mine plus the fact that at launch it was a small metal beam with a 6" steel rod at the end probably moving over 100mph with enough force to break bones

dman762000 · Post by **dman762000** » Sat Mar 03, 2007 10:55 pm

take some bungee cord and dont rely on the hooks on them if thy have them use some big fencing staples and double over the cord on the frame attachment and staple it twice then attach it to the arm and it should hold up and the more trips you make back and fourth between the base and the arm the stronger it will be

vskid · Post by **vskid** » Sat Mar 03, 2007 11:42 pm

If you make a bigger catapult, Mythbusters used surgical tubing.
Catapults seem less powerful and harder to make than trebuchets, except on small scale, because a plastic spoon and food is a catapult.

It would be cool to make a ballista.

khaag · Post by **khaag** » Sat Mar 03, 2007 11:49 pm

Yes, I would use surgical tubing. I think its fairly cheap too? (Don't quote me on that) You can probably get it at a drug store. Bungee cord may have too much "spring" but thats just my 2 cents.

Post by **Triton** » Sun Mar 04, 2007 12:04 am

while it was at the school mine was not a counterweight trebuchet but a tension spring engine. catapults are traditionally a torsion engine (wound cord and the like)

bgnome · Post by **bgnome** » Sun Mar 04, 2007 8:48 am

i saw a model use bike wheel tubing in a book once..

jleemero · Post by **jleemero** » Sun Mar 04, 2007 9:34 am

Nice trebuchet Triton!

I got one... It's a "miniature desktop" trebuchet.

It'll launch a cell phone clear across the room (apparently...)

But anyway, demonofaj, if you're making a true catapult, you don't need anything elastic at all! Just some good ol' nylon rope... A lot of it...

Look at this:

Okay, maybe not the best picture, but still. The rope is simply wound many times to build up tension, you don't need anything elastic or the like.

jleemero · Post by **jleemero** » Sun Mar 04, 2007 9:36 am

Oh, vskid...

Happy birthday

Click here: http://www.thinkgeek.com/geektoys/warfare/81e6/

demonofaj · Post by **demonofaj** » Sun Mar 04, 2007 10:08 am

lol, so bungee cord it is. It is a small scale project, I'm looking for it to at least launch an apple accross a room. The problem with bungee cord though, is that the thing might require so much pulling, it might pull itself off the frame. I'm thinking to staple it down as a base and drown it in epoxy? As for the frame, it's primarily wood, as you guys have shown, and it'll be as we know screwed together.

vskid · Post by **vskid** » Sun Mar 04, 2007 11:49 am

You could tie the bungee cord to your frame.

Rellizate · Post by **Rellizate** » Sun Mar 04, 2007 2:07 pm

Hmm I wouldn't advise tying it. Get a staple gun to secure it after you have tyed it.

dman762000 · Post by **dman762000** » Sun Mar 04, 2007 5:05 pm

big fence staples are better and double the end of bungee over the first staple then staple again