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my semi auto concept

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 semi auto concept

Unread postAuthor: michaelgohjs » Fri May 21, 2010 3:23 am

this is my first post and i learn about this site while researching on how to make a semi auto gun

the aim of this gun is to:
1)use a take of compressed air fixed to gun (pvc tube holding 100-200psi is it safe?)
2) to pressurise a secondary tank and release all the pressure in the secondary tank when i pull the trigger
3) shoot small diameter projectiles (modded nails bout the diameter of a bb and of course bb) just switching a barrel will alow big projectiles but i plane to use nails fixed to a straw(quite stable in flight)
4) be able to shoot multiple shoots before requiring refill (around 10 the more the better)
5)use the pump as little as possble
6)have high accuracy and power (every1 wants that right)

stuff i have access to...
1)pvc pipes and fittings (pressure rated i think will post my current cannon now) and clear pvc glue
2)a car tire compressor (it SAYS on the box its able to pump 300psi)
3) rechargeable batteries (sealed lead acid) to power pump
4) my dad's drill (used only when he is at work @@)
5) some other stuff i dont know how to specify

things i dont have and cant get.. sprinkler valve
metal pipes and fittings (except for the barrel)
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Attachments
test 1.jpg
25.jpg
can some1 help me..does this look let pressure rated pipes?
25.jpg (7.1 KiB) Viewed 1092 times
2010_5_21_16_17_44.jpg
my old air gun..
shoots AA batteries into coconuts..COCONUTS with the husk and so on...frightened my dad when he open a fresh coconut to see a battery inside @@
2010_5_21_16_17_44.jpg (7.32 KiB) Viewed 1092 times

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Unread postAuthor: michaelgohjs » Fri May 21, 2010 3:30 am

ok... let me explain how the gun works..
firstly.. i havent built it.. the 2 pictures up there are to comfirm if i have pressure rated pipes and can they hold 100-200psi safely

now.. refer to picture "test 1"

air enters the secondary chamber through the valve at the bottom until the pressure in the secondary and primary tank is equal (size of secondary take to be decided later after my mid year exams)
then using the slider valve from (http://www.spudfiles.com/forums/viewtopic.php?t=160) i close off my main chamber and release the air behind the piston
the piston flies back and all pressure in the secondary chamber is released into the barrel
when i reconnect the slider valve, the air from the main chamber fills the secondary chamber and closes the barrel-piston getting the gun ready for the next shot.. then when i open the slider valve the whole process starts again
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Unread postAuthor: michaelgohjs » Fri May 21, 2010 3:32 am

please give me constructive input..
i wan to make this a good and advance gun and post it here for every1 to see

-spud together,shoot together because we learn together-
-by myself
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Unread postAuthor: Crna Legija » Fri May 21, 2010 3:47 am

idk if that would work because idk how you want it to work, it would be so much to just make a piston valve and the main valve and concect the big chamber to the small one with a ball valve it will work 100%


this

idk what did i do wrong?


edit: i wouldn't put 200psi in any pvc chamber ever
and if you compressor is made for filling car tires it probly wont last long mabe a week of on of use
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Unread postAuthor: POLAND_SPUD » Fri May 21, 2010 5:10 am

you can build a semiautomatic in two ways:

1. build a valve that opens for a moment and closes. The hammer valve can do that

The advantages:
you only need that valve and 1 tank

The disadvantages:
building the valve is a bit challenging
most hammer valves offer rather lower performance

2. Build a gun that has 2 chambers - firing chamebr and an air tank that provides air for x number of shots

The advantages
good performance
reliability
simple to build

The disadvantages
requires a 3 way valve (or 2 two way valves (for example - ball valves))
requires two tanks
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Unread postAuthor: michaelgohjs » Fri May 21, 2010 5:45 am

poland.. can you give me links or explain abit on the mechanism on the 2 chamber semi auto? cos from what i think.. i feel that my design is in a way a semi auto with 2 chambers.. maybe some links for examples?

emm.. 1 more thing.. is shooting a nail fixed to a straw from a small barrel going to give good range and hitting power.. cos i feel that it is aerodynamically stable as the center of gravity is far enough infront to keep it from tumbling
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Unread postAuthor: POLAND_SPUD » Fri May 21, 2010 6:05 am

check this one -> http://www.spudfiles.com/forums/viewtop ... tml#288103

I've built one like this too... AFAIK there are at least 4 more guns that operate using the same principle
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Unread postAuthor: michaelgohjs » Fri May 21, 2010 6:26 am

thanks man.. i m really happy that i joined this site.. the day i post is the day i get replies and constructive comments ^^
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Unread postAuthor: michaelgohjs » Sat May 22, 2010 7:34 am

emm.. can anyone please give me some constructive comments.. i would really like to do this right and post it here
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Unread postAuthor: POLAND_SPUD » Sat May 22, 2010 8:03 am

I think my post explained it pretty well... IDK what you meant by
stolen tech from slider gun
and what it is... I presume it's some sort of a nerf gun, right ??

well in that case the valve might be just a 3 way valve (is it a valve that first fills the secondary valve and then vents the pilot side ?? if that's the case then it's a 3 way)

anyway... I think I got it right in the first post... I know it's a bit general and all but I wanted to make sure you understand that there are two very broad categories of guns (but you can build hundreds of completely different guns of either type)

If I were you I'd buy a 3 way valve... either a push button valve/lever actuated valve... but you can also use a solenoid valve or a slide valve

If you live in the US and you can't find cheap 3 ways on ebay you can order MJVO-3 from cllippard... add to that a QEV, a couple of fittings and maybe an air cylinder and you've got a semiauto
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