SpudFiles

This is for an upcoming physics project. We're making catapults later this year, but I just don't wanna get caught with my pants down when it comes to a quick release mechanism.

I could do the old "pull the block out from in from of the arm" thing, but I'm trying to make this as efficient as possible, to the point of using base-mount ball bearings, ("pillow block" bearings), for the joint of the arm.

Anyways, this mechanism would hold a 1/8" aluminum pipe down, and be able to release it without the user having his hand anywhere's near it. Only thing I've found so far is some sort of quick-release snap that you pull a collar down on to release, which would earn you a good smack in the back of the hand by the hook on it's trip away from the pipe.

I was considering using some standard-point vice grips for this purpose, but that would involve be extending the handle down below the work surface, (a piece of 2x6" board), and I've also got plans for some sort of clamp system to hold the thing to a desk, so that's out.

If anybody has any ideas, I'd like to hear them. All the "professional" quick-release hooks I found were rated for tremendous loads and very expensive.

P.S. - I also considered quick-release pins, but this would create problems with alignment and mating with the arm, and would probably not have the tensile strength to hold back against two heavy extension springs.

How about get the design from the expensive ones and make your own

Mount two i-hooks on the base, and have one on the arm to go between them, make sure they are very close together, then just slip a steel pin through them. attach a rope to the pin and bingo.

Thats what i did on my trebuchet i built a few years back, it worked like a charm, and still does.

Bah... Be a man and use rope and a sword like they did in the old days.
(Your physics teacher will not question your methods as long as you are holding a sword, by the way:)

But really, what paaiyan suggested is probably the best idea for the effort involved. You could make special ihooks with some roll-bearings in them if you are worried about friction, but I prefer the "Get more people to pull on it" method.

Edit: how the hell do you pronounce "paaiyan"?

_Fnord wrote:Bah... Be a man and use rope and a sword like they did in the old days.
(Your physics teacher will not question your methods as long as you are holding a sword, by the way:)

But really, what paaiyan suggested is probably the best idea for the effort involved. You could make special ihooks with some roll-bearings in them if you are worried about friction, but I prefer the "Get more people to pull on it" method.

Edit: how the hell do you pronounce "paaiyan"?

I do like the sword idea. And I happen to have one...

And to be completely honest with you, I haven't got a clue. It's about the closest I could find to the Olde-English word for pariah, but nobody I asked knew how to pronounce it. Pretty soon I'm going to be starting a web-design business from my home under that name, so I'll just have to make somethign up.

I think it is pronounced Payy-ennn, like in Major Pain "You want a little something to take your mind off that pain?" 8)

This might work... Take an old barrel sealing piston gun. Take the barrel off. Do what paaiyan said, but without the rope. Instead, screw one end of the release pin into the piston. Put the pin through the i-hooks so that the trebuchet is ready to fire. Charge up the gun, but not to any pressure greater than 30 psi for hearing protection. When you shoot it, the piston should pull the pin out when it moves back to unseal the barrel. It makes sense when I think about it...

I had an epiphany last night.

I'm gonna use a push-to-connect quick disconnect coupling for this purpose. The arm will have a male quick-disconnect on it, and the female Q.D. will be mounted in the base. I'm gonna find an old choke cable and clamp it to the sleeve of the Q.D. for firing.

I'm not sure a quick connect will take the forces involved.

I had an incident a couple years ago were a piece of pipe was blasted 30ft into the air while a quick-connect was hooked up to it, and the two halves seamed to separate easily.

You may have to modify one before it will work right.

That's all part of the design. The springs are at the level that when the Q.D. is locked into place, they are pulling the arm more towards the base then away from the Q.D. Once released, the arm will move forward and more force will be applied pulling the arm.

why not use some kind of explosive bolt like they use in the space shuttle........

that would go over REALLY big................ lol

anyway, just tie the thing down with VISCO fuze. light the fuse, and when it burns the knot, FLINGGGG (what sound does a catapult make?)

Heh... that wouldn't go over too well simply because the tests are indoors. I don't think a science lab full of smoke is very pleasant to stay in.

BTW, this catapult should actually make a thumping sound because I'm installing rubber bumpers to stop the arm at around 45 degrees. Actual angle still depends on what I'm launching, (the CD value). I thought about miniature shock absorbers but they'd be too expensive unless I made them myself.

I take it the quick-releases Mythbusters use are too expensive
I've used some sort of butterfly spring bolty thingyamajig before as a trigger for a nail gun that is tensed with a rubber band.

It did the job but I don't think it can be used for this application, it held the nail in between a butterfly spring clamp.

Which had two springs, one on each wing which forced it outwards, so to jam something in, you simply push the wings together, jam something in between, let the wings go, now your rope/whatever is jammed in, then to fire simply push them together again.

P.S Love the new avatar

Well you could do what I'm going to for my trebuchet. Tie off a rope and cut it with a sword.