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custom auto valve

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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custom auto valve

Unread postAuthor: jackssmirkingrevenge » Tue Jan 20, 2009 1:30 pm

Just look at it go :D

[youtube]http://www.youtube.com/watch?v=w8e9Z5t1NDs[/youtube]

After this less than succesful (in terms of power) experimentation, I decided to take a step back and examine what wasn't right about the design, and came up with the following:

-too little flow, stemming from a relatively small port and a stiff spring that didn't really let the piston pop that much

-a lot of air was being wasted flowing past the piston instead of through the port

I set about trying to improve the design in such a manner that the above problems would be eliminated. The first issue was simply solved by scaling up the design by doubling the port size and tripling the piston size. I also made the piston out of a syringe, that not only greatly facilitated construction but gave me an airtight seal ensuring air could only escape through the port.

As an added benefit, this allowed me to eliminate mechanical springs and simply use a pneumatic one by pressurising the area behind the piston, meaning I can easily vary strength by changing the pressure.

It moves a lot more air and there certainly is potential, note how it rocks with the pipe unsupported:

[youtube]http://www.youtube.com/watch?v=MEDr793kRV8 [/youtube]

I'd say the idea certainly has more potential now, watch this space :D

Here's what it looks like and a rough diagram of the internals:
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Unread postAuthor: Hubb » Tue Jan 20, 2009 1:35 pm

And, yet, it seems so simple... :wink:

Nice work.
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Unread postAuthor: JDP12 » Tue Jan 20, 2009 1:38 pm

wow.... very impressive JSR.

your quest for full auto never quite seems to end :D
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Unread postAuthor: Ragnarok » Tue Jan 20, 2009 2:12 pm

I'm going to have to link back to a year old post of mine... here
Aside from the fact that you're using an air spring rather than a mechanical one, your design is essentially identical to what I was talking about back then.

...In other words, I told you a design like this would work over a year ago, but did you listen? :tongue3:

*Prepares for the inevitable counter attack*
:toothy2:
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 20, 2009 2:18 pm

Cheers guys :)

git wrote:Aside from the fact that you're using an air spring rather than a pneumatic one, your design is essentially identical to what I was talking about back then.


... and essentially identical to how most pop-off valves work, so no one can really claim originality - but yes, granted, I was needlessly sceptical :? I'll pay more attention next time :D
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Unread postAuthor: Ragnarok » Tue Jan 20, 2009 2:37 pm

jackssmirkingrevenge wrote:and essentially identical to how most pop-off valves work, so no one can really claim originality

Yes, I admit that. I'm not here to claim originality for it - indeed, most of my ideas are either intentional modifications of something else, or are something where I've just reached the conclusion independently.

Now, there are a handful of ideas I've had which I consider reasonably original, but I haven't shared most of those yet...

Anyway, I forgot to congratulate you on getting it to work - good job.
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Unread postAuthor: LCTChamp » Tue Jan 20, 2009 2:38 pm

Great to see it working. Now all you need to do is put a barrel and loading system on. I can't wait to see some damage pictures/videos.
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Unread postAuthor: ALIHISGREAT » Tue Jan 20, 2009 2:44 pm

congratulations.... now hook up a blow forward bolt and shoot you some bbs.
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Unread postAuthor: Hotwired » Tue Jan 20, 2009 2:46 pm

Looks good. Finally a cyclic rate you can see :)

I actually suspect it's the friction of the syringe plunger that's keeping the ROF down, the triple rubber seals are quite a tight fit which they have to be of course but it also provides resistance to the piston moving.

Beware the heat and wear from friction between the rubber and plastic in the syringe piston in substantial use.
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Unread postAuthor: Ragnarok » Tue Jan 20, 2009 3:28 pm

For those who are wondering, I've just downloaded the video file of this and ripped the audio stream from it to figure out the rate of fire.

The ROF looks to be bang on 220 rpm at the moment, and pretty damn consistent timing between bursts. This consistency says good things for what's going to happen should a breech be attached - the system isn't so finely balanced that throwing that in there would disrupt it.
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Unread postAuthor: POLAND_SPUD » Tue Jan 20, 2009 4:35 pm

I actually suspect it's the friction of the syringe plunger that's keeping the ROF down
silicone oil should help with that...
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Unread postAuthor: Skywalker » Tue Jan 20, 2009 4:46 pm

Good work! So, IIRC the last time a design like this came up, people decided that it wouldn't work unless there were some sort of valve coupled to the piston to shut off the air flow from the compressor/reservior to the firing chamber. Looks like we were wrong!
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Unread postAuthor: ALIHISGREAT » Tue Jan 20, 2009 4:49 pm

POLAND_SPUD wrote:
I actually suspect it's the friction of the syringe plunger that's keeping the ROF down
silicone oil should help with that...


yeah but JSR's creations arn't usually modular... i would be surprised if he could take it apart to lube it... although he could squirt some in through the schrader on top of the air spring i suppose...
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Unread postAuthor: sputnick » Tue Jan 20, 2009 5:00 pm

VERY impressive, and suprisingly simple!

Needless to say, if this works with barrel and breech assembly, you will have made an enormous leap in the field of homemade pneumatic guns.

Do you think it could be stepped up to a paintball size? or would the air required just be too ridiculous?

Edit: What happens behind your piston, as in, do you need to re-adjust the balast pressure every once in a while? I would think it would vary, seeing as almost nothing is 100% airtight
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Last edited by sputnick on Tue Jan 20, 2009 5:38 pm, edited 1 time in total.
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Unread postAuthor: Sticky_Tape » Tue Jan 20, 2009 5:23 pm

DAMN!? Ww that is just great I think I know what I will be building concidering I have myself a bfb. Oh yes and if anybody wants to make this but doesn't have acess to syringes you can use a floating o-ring.
Also no air wasted by piloting valves *applause*.
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You can tell how awesome a cannon is by the pressure used.
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