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Unread postAuthor: wngovr » Sun Sep 26, 2010 10:56 pm

Thanks for the comments guys.

Technician, that makes since now that I think about it. More torq than speed I guess.

I think the easiest fix now is to take gun freaks idea of puting a sealed piston on the front of the spring and getting a new barrel to make a compression chamber. then putting a smaller barrel at the end of that to load the projectile into.

I dont think I can use the regular C/B ratio since the chamber wont be pressurised untill the piston gets halfway down the chamber. so if the chamber is 1.25 inches by 10 inches and the barrel has a .375 inch ID, any idea how long the barrel should be or do I just experiment?

Will this idea even work?
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 26, 2010 11:12 pm

feck! arse!

beautiful!

But of you can cock it manually without much difficulty not using a lever, it's not going to be that powerful...
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Unread postAuthor: Technician1002 » Sun Sep 26, 2010 11:20 pm

wngovr wrote: I dont think I can use the regular C/B ratio since the chamber wont be pressurised untill the piston gets halfway down the chamber. so if the chamber is 1.25 inches by 10 inches and the barrel has a .375 inch ID, any idea how long the barrel should be or do I just experiment?

Will this idea even work?


This idea works. It is used in "Springer" guns. Be sure you understand the pressure your spring is pressing against on it's travel. At 1/2 way down the air chamber, the volume of air is 1/2 so not counting compression heating effects, the pressure goes from 1 atm to 2 atm, or about 15 PSI. The math for springers is a little complicated. One of our physics experts may be able to better help with the nitty gritty of how to balance the chamber size, spring size, and barrel size. Done incorrectly results in the piston busting out the end of the air chamber.
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Unread postAuthor: jackssmirkingrevenge » Sun Sep 26, 2010 11:23 pm

Technician1002 wrote:The math for springers is a little complicated.


That's a substantial understatement :wink: you're probably better off taking an existing succesful commercial design and copying the dimensions...
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Unread postAuthor: Gippeto » Sun Sep 26, 2010 11:43 pm

Nice work. :)

If you can convert it to a "hammer valve piloted co-ax", something like this, will perform better than many a crossbow. :twisted:

http://www.youtube.com/watch?v=FGOT1c9m_F8
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Unread postAuthor: Crna Legija » Mon Sep 27, 2010 4:34 am

you probably already have this but do you have a dent holding you ammo in to build up pressure before it pops out?
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Unread postAuthor: inonickname » Mon Sep 27, 2010 6:36 am

-_- wrote:you probably already have this but do you have a dent holding you ammo in to build up pressure before it pops out?


It doesn't need a detent. It's a crossbow, with a spring instead of limbs and a string.

You need the lightest spring you can get, while still having a reasonable draw. Or, just use REALLY heavy ammo to take advantage of the springs strength. You could probably convert it to a springer, but you'll probably still need a lighter spring.

As you have machining facilities, consider a gas spring. You should be able to make one to fit without drastic changes. A gas spring will be slightly less powerful than an equivalent draw weight steel spring, but it can be left compressed without losing power, will never fatigue and is completely adjustable. Plus, they can be made quite light.
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Unread postAuthor: Fnord » Mon Sep 27, 2010 12:29 pm

Are you intent on making this look like a gun or can it have bow aspects as well? For a simple design I'd just build something like a slingshot(tons of examples in the slingshot thread).

However, personally I'd just make an all-wood recurve war bow, with a fiberglass backing if I was desperate. With the right design I bet I could beat his crossbow in terms of power.

If you're willing to devote time to learning a trade such as this I can probably give some useful advice. There is nothing mystical about making a powerful and efficient bow, but there are counter-intuitive aspects to it.
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Unread postAuthor: MRR » Mon Sep 27, 2010 1:55 pm

I'm with inonickname on this one.
For example Jörg Spräve our slingshot expert here on the forum experimented with different kind of rubber bands to optimize the performance of his creations. He learned that thin, easy to draw, rubber bands accelerate lighter projectiles better than thick ones.

So, one possible option would be like inonickname suggested, using an extreme light pressure spring or you do it the other way around and use two even lighter tension springs, like it have been done before on slingshots.
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Unread postAuthor: wngovr » Mon Sep 27, 2010 5:03 pm

Can anyone give explanations or links that explain these things?

Captive bolt firing system.

Gas spring.

I guess I don't know how to use the search function. I get 800 pages of stuff that doesn't seem to help.

Thanks
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Unread postAuthor: clemsonguy1125 » Mon Sep 27, 2010 5:19 pm

Also does your ammo have a good seal, if not air is just escaping around it, it looks great so far.
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Unread postAuthor: Lockednloaded » Mon Sep 27, 2010 5:41 pm

Captive bolt firing is basically a saboted dart, but the sabot never leaves the barrel. It works kind of like an air nailer, except that it shoots larger darts :lol: . The sabot is full bore and slides back and forth. To keep the sabot from leaving the barrel, and keeping the dart straight, the endo of the barrel is much smaller.

:EDIT:
Found it
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