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Help With Semi Auto Ideas

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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Help With Semi Auto Ideas

Unread postAuthor: KiLlFrEnZY » Wed Sep 29, 2010 4:05 am

My first post be nice 8)

Would anyone be so kind as in to point me in the right direction...... what im trying to do is build a semi auto Pneumatic that preferably runs off a tank / chamber / reservoir of compressed air.......and not a compressor.

ive looked around and found things here and there but im really lost in what is better to do.... sprinkler valves vs other contraptions...... i have a general idea of how its goin to work..... but still verryyyy unsure

what i want out of the gun isnt reallly much 6 or so shots will make me happy and i dont need very long range..... i plan to fire homemade darts... or even like the "nerf" darts and yeh...lightweight stuff and i would prefer something gun like i.e. has a trigger and not like random ball valves to shoot.....

oh and i have made a Pneumatic Cannon before so i kinda building from what i learnt from that.....

my somewhat plan goes like this..... (duno if it will work)
ive got no measurement or sizes this is just in my head.....

basically you have one tank with the air inside of it.... this then connects to a ball valve or something similar which then goes to a second smaller chamber .... idea here is i pump main chamber turn valve on/off really quick and put small amount of pressure into smaller 2nd chamber.....(if that makes sence?) next step you have that smaller chamber connect to a modified sprinkler valve with blowgun attached.... i assume you squeeze the trigger and it releases the air tru the valve ..... from there it enters the barell pushing out my projectile....... thats what i have so far......

any ideas or ways to improve or any info would be reallly nice ty all

Moderator edit by MrCrowley: Topic title.
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Unread postAuthor: lozz08 » Wed Sep 29, 2010 5:17 am

Your description sounds like it won't actually give you semi auto, because you have to refill the smaller chamber after every shot. As long as you understand and accept that, the design will meet your expectations.

I would suggest the following;

Purchase a quick exhaust valve. Pick a size that matches your ammo. Connect everything together with brass fittings of that size.
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Unread postAuthor: KiLlFrEnZY » Wed Sep 29, 2010 5:22 am

Yeh i was trying to think of a way the mechanizes that part of it.....but yeh any ideas how i could like bypass that kinda stage..... will getting rid of that 2nd chamber idea and just making it connect straight to the main tank work? asin when i squeeze and let go will there still be left over air.... for a second third? shot..... or will it just all escape..... im thinking it will just all leave at once


thanks for the tips
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Unread postAuthor: lemming124 » Wed Sep 29, 2010 7:49 am

for semi I would suggest a hammer valve design like this: http://www.spudfiles.com/forums/t-t17827.html

but not quite as complicated:
http://www.spudfiles.com/forums/hammer- ... 17843.html

If your not fussed about it being semi then two chambers (a large main and small firing chamber filled by he main chamber) separated by a ball would work fine. you wouldn't need to worry about opening and closing the ball valve quickly as the firing chamber would be relatively small so pressure would decrease slowly enough for a few shots. like this:
http://www.spudfiles.com/forums/my-plinker-t16854.html[/url]
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Unread postAuthor: Big-E » Wed Sep 29, 2010 12:56 pm

Look at my project, may give you some ideas:

http://www.spudfiles.com/forums/thunderbess-edit-major-update-t20806.html

If you charge the gun prior to each shot from a reserve tank, like I do, you can't make a true semi auto. you can, however, make a repeater.

Semi-auto means each trigger pull, it shoots, you can do it with a hammer valve, or mechanically.

some people say old shatterhand is a semi, but, if I recall correctly, he has to cock the hammer for each shot, so it's considered a repeater. Think of a daisy bb gun; It's not semi-auto in that you need to cock it's lever for each shot.

so, as you can see, you can easily make a repeating system, but if you want true semi automatic operation, you need to cycle that process automatically every time after the first shot .

My pneumatic could easily become a repeater, I just add a magazine and a detent. For Semi auto, I would need to rework my design.

Just trying to clear things up a bit :D

BTW, Thunderbess can use nerf darts (clip-system type darts) If I set the reg around 20 PSI, at 50 PSI they fly really straight far and fast, and can punch holes through a cardboard box easily! so run either a tiny firing chamber or keep your pressure low if you plan to skirmish with it.
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Unread postAuthor: Gun Freak » Wed Sep 29, 2010 4:47 pm

Here is a good setup.
Large chamber of PVC, probably 2" by 3' wood be good>1" ball valve cracked to let a little air through>18 or so inches of 1" pvc>Modded sprinkler valve, which gives you the trigger feel and good performance.
The gun fills itself with the large chamber while not exhausting all the air in one shot. Get it?
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Unread postAuthor: KiLlFrEnZY » Wed Sep 29, 2010 6:53 pm

good ideas guys..... :) nice...... i really like Big-E's thunderbess there just only one thing i dont get..... im not to sure how the concept of the blow gun on the brass tee join works..... can someone please explain this to me briefly in noob-ified terms so i get a general idea on whats happening....... but yeh also second question that came up was with the suggestion of the hammer valve i like this but i cant seem to figure how i would trigger it with like a trigger design ( probably really easy..... i just didnt click)
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Unread postAuthor: Gun Freak » Wed Sep 29, 2010 6:57 pm

The simplest and easiest way would be the one I suggested, but BigE's uses a storebought QEV, which is very powerful but they can be expensive unless you get them off like Ebay. They are easy to use though.
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Unread postAuthor: clemsonguy1125 » Wed Sep 29, 2010 7:11 pm

Mines a basic piston valve chamber filled with a detent and t mag
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Last edited by clemsonguy1125 on Thu Sep 30, 2010 6:16 pm, edited 1 time in total.
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Unread postAuthor: lozz08 » Wed Sep 29, 2010 7:42 pm

A problem for you is going to be power consistency. With a chamber of compressed air without a regulator, each shot will get weaker as the chamber empties. If you dont know how far a shot is going to go, it can be hard to aim it.
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Unread postAuthor: KiLlFrEnZY » Wed Sep 29, 2010 8:11 pm

A problem for you is going to be power consistency.


thats true......hmmmm.......... :? would having a increased in pressure help? or.... like since it will only shoot 6 darts before a reload / re-pump i believe it should be enough :? ..any shots after that will be just bonus i guess?

hmmm so far my plan is still the

chamber(Main) => ball valve => chamber(firing) => sprinkler

what do yous think of this performance wise?

im ok with the "repeater" design basically anything that will give more than one shot then pump one shot pump etc. is good enough for me :wink: :wink:

oh and one more thing like i said before how would i go about triggering a hammer valve.... how is it being done now? is it not kinda hard to press it with one finger at higher pressures?
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Unread postAuthor: lozz08 » Wed Sep 29, 2010 9:48 pm

I don't see any benefit to you using a hammer valve for now... put a pressure gauge on the small chamber and make only a small hole between the two chambers so that you can control what pressure you will fire at.

Fill the main chamber to as high a pressure as you can, and use the ball valve to fill the small chamber to say 80 psi on the dial.
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Unread postAuthor: jackssmirkingrevenge » Wed Sep 29, 2010 11:46 pm

Since you're not after dramatic performance, why not just use a blowgun directly? With reasonable pressure and a long barrel performance is nothing to scoff at.

No need to make separate firing and main resevoirs, or deal with the relative complexities of a hammer valve.
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Unread postAuthor: Gun Freak » Thu Sep 30, 2010 6:03 pm

@Jack I think he wants bigger calliber than what a blowgun valve is good for.
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Unread postAuthor: KiLlFrEnZY » Fri Oct 01, 2010 3:33 am

hey guys because i plan to use a magazine to load the ammo.... does my barrel need to be 100% airtight??? like after the sprinkler valve?
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