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Full Auto 50

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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Full Auto 50

Unread postAuthor: kustomkb » Thu Feb 20, 2014 11:02 pm

Inspired by e_smith2000's AA gun, ( pneumatic-cannon-database/topic23527.html ) I started on one of my own.



Here is a screen shot of the basic design;



I started on a jar-top valve mod.

The solenoid thread is 3/4-20. I had the tap on hand, so I chucked up the lid;

Image


And popped out the centre bit with an end mill;

Image


Then finished bored to the tap drill size;

Image


Then continued the threads, through to the inside;

Image


I then turned and threaded an insert to match;

Image Image


A generous chamfer was added to capture and seat the o-ring;

Image


And together;

Image


Here are some of the other parts in progress;

Image

Image



Mr Smith has a PVC tank in between the air supply and the valve. Is there any need for this if you are running from an air compressor. A bit of a reservoir charging up while the gun is firing?

What would be a good shape for the projectile?

Thanks!

-KB
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Re: Full Auto 50

Unread postAuthor: mobile chernobyl » Fri Feb 21, 2014 10:28 am

Very nice work! Something funny about seeing precisely machined threaded inserts made for a $20 sprinkler valve lol - but it's all for the love of the hobby!

There is a choke/bottle neck effect though between the air supply and the reservoir - that the reservoir helps in pre-dosing your volume of air delivered to the projectile! Considering the air supply from a long, small diameter hose will flow significantly less then the air supply from a 3/4 or 1inch threaded connector, with extremely short tube (relative to the supply hose), you can "assume" that the air in the buffer chamber will dump completely and use that as a calculation point for your projectile's performance. The reality of this is that it would require a differential equation setup to calculate the actual air usage, but it's somewhat safe to assume the air in the reservoir can be assumed to imitate a conventional chamber in a closed system for your GGDT simulations.
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Re: Full Auto 50

Unread postAuthor: kustomkb » Fri Feb 21, 2014 5:29 pm

Thanks MC.

Yeah, the fitting s definitely worth more than the valve...No disrespect to epoxy, but I prefer a mechanical connection whenever possible. And I had the means, so why not.

Thanks for the detailed explanation of the reservoir. The part I understood makes sense. :lol:

The boys were having a little nap so I ducked out to the shop, hooked it up to an 80 PSI airline, and gave it a quick test;





Oh dear. What have I done?

I will need a stronger spring and probably change the piston to Delrin or something, because the bronze piston makes it feel like a bloody jack-hammer! -Very realistic for sure.

Surely a plastic valve, cycling at that kind of rate, will lead to some kind of failure?

I will carry on with the build and appreciate all criticisms and advice.


Thanks,

KB
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Re: Full Auto 50

Unread postAuthor: jackssmirkingrevenge » Sat Feb 22, 2014 7:37 am

Looking very tasty!

Welcome to the world of angry wasps and farting machines :) first world spudder problems since 2007

Are you pulsing the air from the valve? If not, I'm afraid this endeavour is doomed to failure.

It's only with a pop-off pilot that you can get the blow forward to cycle reliably in a controlled fashion:



What would be a good shape for the projectile?


A tube closed off at one end will suit you fine.

Image

Image
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Re: Full Auto 50

Unread postAuthor: kustomkb » Sat Feb 22, 2014 10:55 pm

"Doomed to failure" !!?? But, but, well... I'll show you!!!

Just kidding. I know you guys have all been down this road before. I saw a you tube vid and dove in. My time for research and understanding is extremely limited. So, again, I really appreciate the guidance and suggestions given.
I think I am pretty good at building things, but am not so well versed in the theory.

If you don't mind elaborating on the pop-off pilot, I could understand.

I had this valve set-up for the diaphragm pilot;

Image

It seemed the small diameter tubing, or length of it, was not enough to activate the valve. I switched to the blow gun and it would actuate.


So just now I tried another route, and it would seem the sprinkler valve was doing nothing except opening and closing the air line;




Sounds cool anyways...

The coolest sounding fart I ever heard.


.
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Re: Full Auto 50

Unread postAuthor: jackssmirkingrevenge » Sun Feb 23, 2014 2:53 am

The problem with your little spring loaded ball setup is that it doesn't pop, it just leaks. A true pop-off valve uses a piston which when moved slightly, exposes a shoulder to pressure which moves violently to dump air. You can see it in a home brewed pop-off I had made using a syringe and liberal quantities of epoxy:



Try using one of these as a pilot:

Image
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Re: Full Auto 50

Unread postAuthor: kustomkb » Sun Feb 23, 2014 10:24 am

Ah, I see what you mean,

Thanks, I'll give it a try.
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Re: Full Auto 50

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Re: Full Auto 50

Unread postAuthor: POLAND_SPUD » Sun Feb 23, 2014 10:37 am

Allow me to use my standard response... You need a DCV valve :-D

Seriously why waste time trying to tweak it when you can provide pulsed air supply for it with a solenoid valve. The added advantage is that you can have adjustable ROF and no compromises are needed
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Re: Full Auto 50

Unread postAuthor: jackssmirkingrevenge » Sun Feb 23, 2014 11:58 am

POLAND_SPUD wrote:Seriously why waste time trying to tweak it when you can provide pulsed air supply for it with a solenoid valve. The added advantage is that you can have adjustable ROF and no compromises are needed


It's not always fun to rope in electronics though, but it seems to work for paintball. Speaking of which, a Spyder E-MR5 recently entered the scrap box...
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Re: Full Auto 50

Unread postAuthor: kustomkb » Fri Feb 28, 2014 7:40 pm

Thanks again for the ideas.

I picked up a pressure relief valve, rated for 140 psi. I put in a lighter spring and here is the result;




It's a lot louder than the video suggests.

I also remembered I had this adjustable valve;

Image

I don't have much time in the shop, so I'll report back in a while.

Cheers.
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Re: Full Auto 50

Unread postAuthor: Gippeto » Sat Mar 01, 2014 1:31 am

Have a lot of Swagloc stuff just laying around do you? :)

Watching with interest.
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Re: Full Auto 50

Unread postAuthor: jackssmirkingrevenge » Sun Mar 02, 2014 9:00 am

kustomkb wrote:It's a lot louder than the video suggests.


It always is, this does not seem to loud but was hurting my ears:



Looking good, let's see this thing empty a magazine :)

Gippeto wrote:Have a lot of Swagloc stuff just laying around do you? :)


Image

:D :D :D
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Re: Full Auto 50

Unread postAuthor: kustomkb » Sun Mar 02, 2014 10:29 am

Have a lot of Swagloc stuff just laying around do you? :)


I used to work at a place that would toss this stuff if it became contaminated. Being a bit of a pack rat, I couldn't bare to see it in the trash.

JSR, sorry, I don't get the Canadian reference;

Image

Looking good, let's see this thing empty a magazine :)


I have got three rounds out the barrel in a semi-auto fashion. I still need a heavier return spring for full-auto. I can't find it and will need to make my own...
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Re: Full Auto 50

Unread postAuthor: Talk » Sun Mar 02, 2014 2:13 pm

Since you have some machining skills, you can make a steel body for that and give it a Thompson SMG design
Thopmson.jpg
Thopmson.jpg (39.52 KiB) Viewed 1962 times

I don't have any resources to build guns so I thought I could give it to someone who can build these.
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Re: Full Auto 50

Unread postAuthor: jackssmirkingrevenge » Sun Mar 02, 2014 7:52 pm

kustomkb wrote:JSR, sorry, I don't get the Canadian reference


I meant it was a Canadian thing to have swageloc stuff lying around :) don't worry, we're on the same side of the border ;)
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