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Multi-shot nerf concept

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Multi-shot nerf concept

Unread postAuthor: FishBoy » Tue Jul 29, 2008 7:34 pm

okay, here is my concept for a multi-shot nerf gun. It consists of a large primary air chamber which fills a very small firing chamber via a ball valve, the ball valve is closed, and then a modded sprinkler valve is used as the firing valve. I was wondering, what would be a good operating pressure, and how many shots do you think I could get with it? (note- 1" firing chamber will most likely be smaller than shown in the picture, it will probably be 1/2"-2" long)

edit- click the pic to read it better
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Unread postAuthor: Mr.Sandman » Tue Jul 29, 2008 7:37 pm

it would work but your shots would get less and less powerful maybe you could upgrade to 3 inch pvc for the chamber
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Unread postAuthor: Big Boom » Tue Jul 29, 2008 7:40 pm

But you would still have to reload it, correct?
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Unread postAuthor: FishBoy » Tue Jul 29, 2008 7:48 pm

yes, but not refill it, I am considering a sliding breach if I make an additional longer barrel
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Unread postAuthor: iknowmy3tables » Tue Jul 29, 2008 8:32 pm

well sadly sprinkler valves, because the way the operate, do not close immediately when a very sudden increase of pressure is introduced, like from opening the ball valve quickly, you would have to open it so slowly and carefully it would kill the fun, it is possible that you could leave the ball valve slightly open, but in that case I would recommend a needle or gate valve to regulate flow better. the best solution would be to use a ball valve instead of a sprinkler valve
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Unread postAuthor: FishBoy » Tue Jul 29, 2008 8:53 pm

how much pressure do you think would be wasted?
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Unread postAuthor: mobile chernobyl » Tue Jul 29, 2008 9:04 pm

For a cheap project like this, and a fun one to accomplish what you want - make it pump action!

Have 2 valves linked together indirectly. When one is closed, the others open, and vice versa. This can be done by tying them together with a linkage. However if just directly tied together you will have a point where both valves are open 50%. To fix this put some "give" in the linkage AKA have it slide a few inches to create a "dead spot" and a little spring to keep the slide centered when not "cocking". The benefit of having the linear cocking motion is... if you really wanted to be creative... throw in a bolt and a spring loaded magazine for a faster shooting semi! NEEEET-O DEWD

I don't really feel like drawing it up :lol: Sorry, Busy enough here (OK if more people than just you are interested in this design, let me know and I will draw and "scan" a rough sketch for you guys, cause I don't think I've seen this method implemented here on spudfiles and its darn cool!) If you understand it, good, if not, just go with what you were planning, it'll work alright as well, but you'll spend more lol. Since this is just a nerf gun, i figured my double ball valve idea would be more than adequate.

Good luck!
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Unread postAuthor: FishBoy » Tue Jul 29, 2008 9:52 pm

could you give a diagram perhaps?
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Unread postAuthor: mobile chernobyl » Tue Jul 29, 2008 9:58 pm

I'm working on my Semi auto spool valve design right now, kinda in a productive groove so i don't feel like derailling, sorry. Perhaps tomarrow. It's not a really hard concept, but I guess I'm just not good at explaining it easily. :?
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Unread postAuthor: iknowmy3tables » Wed Jul 30, 2008 2:52 pm

FishBoy wrote:how much pressure do you think would be wasted?

in which setup? if you're talking about how much air would leak out if the ball valve were suddenly opened; it would depends on the pressure, how fast you open the valve, and the quality of your sprinkler valve, but you can take into account that the chamber size is quite small which means the chamber will pressurize very quickly, so it is likely to be pretty bad.
If you're talking about how much air would be wasted if the valve is left open slightly to slowly fill, again it depends, on the pressure, the sprinkler valve, but also it depends on how far open the valve is, and how long you hold the sprinkler valve open. And once again the small chamber size will present a major factor in our assumption. the task seems way too difficult to regulate the flow to a right amount using a 1" ball valve, you would defiantly need a more precise valve.

I would recommend moving toward a slightly different approach if you really want to use a sprinkler valve, Since there is no need for a high flow connection between the big chamber and little chamber, you can design the gun with a large chamber made from a section of large pipe and 2 end caps, large pipe (although most stores don't sell sch40 fitting larger than 2" they still sell large end caps in sch40) that is attached to the smaller chamber with a vinyl tube
examples
Image
Image
Image

but note the flow restriction from the vinyl tube may not slow flow enough to directly connect to the chamber and not waste significant amounts of air immediately after firing, you could use a blowgun or small ball valve to cut off flow to the small chamber, or you could try plugging one of the vinyl tube fittings with epoxy and drill a pinhole in the epoxy
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