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My Pneumatic Crossbow Prototype

Built a pneumatic cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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My Pneumatic Crossbow Prototype

Unread postAuthor: jor2daje » Tue Nov 18, 2008 7:22 pm

This is my attempt at a pneumatic crossbow, I know jsr has already made one and its probably better.

I got a cheap fiberglass bow from a garage sale for $2.00 it had no handle or anything so I decided to use it to make a crossbow with of an old 2x4 I had. I just carved out a simple stock and made a really easy trigger mechanism. Then I thought I might make it like a Nerf gun or spring airsoft gun. I got some 1.25" pvc for the chamber and 1" fits really snug inside of it so I used it for my piston. To push my piston I use a golf club shaft because of its light weight, I just put a piece of wood with a notch on the end to catch the string. And the barrel is .75" pvc

It shoots basically anything that fits down the barrel, i have only tried some lemons and a homemade dart so far but I was able to shoot the lemon well out of my yard (I didn't aim up with the dart haha)

Feel free to ask any questions.
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Attachments
1118081606-01.jpg
trigger mechanism
1118081607-00.jpg
side view of trigger
1118081606-02.jpg
barrel and piston assembly
pistonbow.jpg
The full bow
pistonbow.jpg (5.3 KiB) Viewed 2933 times
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Unread postAuthor: covey12 » Tue Nov 18, 2008 7:25 pm

sweet, damage pics?
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Unread postAuthor: VH_man » Tue Nov 18, 2008 7:34 pm

Looks Sweet. What did you use as a Piston Seal?
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Unread postAuthor: Cosmic Muffin » Tue Nov 18, 2008 7:53 pm

aha what a beauty
at first glance it doesn't look to powerful, but if is shoots a lemon out of your yard then it must be pretty good.
advice? well the end of the piston rod where you have the wood dowel, you should probably smooth it out to avoid damaging the string.
do you know what poundage the bow is?
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Unread postAuthor: jor2daje » Tue Nov 18, 2008 7:59 pm

to seal the piston i used rubber, hot glue and a lot of wax.

And i don't know what the poundage is sorry
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Unread postAuthor: Ragnarok » Tue Nov 18, 2008 8:05 pm

I'm going to have to call you on that trigger mechanism. You really want to be lifting the string off the catch/holder, not pushing it off. What you have there is not far removed from blunted scissors rubbing against the string, so I have to express worry you might damage the string and have it suddenly fly wildly, which could cause injury.

Other than that, looks nice enough to me, although, anything based around this mechanism is going to be rather less efficent than the bow alone.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: jor2daje » Tue Nov 18, 2008 8:19 pm

I know the trigger really sucks haha but as I said I threw the whole cross bow together in basically a day. I'm pretty much just happy that it works.
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Unread postAuthor: LikimysCrotchus5 » Tue Nov 18, 2008 10:38 pm

Can you explain a little on how it works?

I am slightly confused on how the barrel is sealed and how it is that when the string rapidly moves forward it actuates it.

I did look at JSR's diagrams but i am still unsure.

Is it air that propels the projectile or momentum from a piece of rod?
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4SPC, My 4" piston 3" porting cannon
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Unread postAuthor: jor2daje » Tue Nov 18, 2008 10:41 pm

Its the air its just like a nerf gun or a spring airsoft gun. There is a piston that seals with the chamber, it is propelled forward very quickly compressing the air in the chamber which expands out through the barrel. The rod simply pushes this piston, and does not actually touch the projectile.
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Unread postAuthor: starman » Tue Nov 18, 2008 10:59 pm

Pretty neat concept. I haven't seen JSRs model of this (I don't think anyway).

What I like about it is not being tied down to bolts or arrows and allowing more conventional ammo usage...marbles, shot or darts. I suspect however because of so many exchanges of energy, power and efficiency has to be fairly low.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 19, 2008 12:44 am

starman wrote:Pretty neat concept. I haven't seen JSRs model of this (I don't think anyway).


here.

Good work jor2daje, action videos please :)
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Unread postAuthor: Cosmic Muffin » Wed Nov 19, 2008 5:38 am

yer some vids of the action would be good. does the bow string ever miss the wood bit?
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Unread postAuthor: jor2daje » Thu Nov 20, 2008 12:39 am

Sorry no video yet. And no the string hasn't missed the wood yet.
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Unread postAuthor: Cosmic Muffin » Sun Nov 23, 2008 7:16 pm

it sounds pretty efficient then, good job mate :wink:
i have a 34 lb samick in the shed, but I'm not sure about donating it to spud research just yet :D although 34lb could do some good damage :wink:
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Unread postAuthor: VH_man » Sun Nov 23, 2008 10:08 pm

My friend has a childrens bow..... I wonder if you could modify one of theese to be airsoft style......
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