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Mk IV QEV Popoff. Updated 22 Feb

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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Unread postAuthor: inonickname » Mon Apr 27, 2009 8:39 am

Very impressive work there! (you must have a good vise for your press, while I could probably replicate that it would be VERY hard with my vise..)

The first thing that struck me was that you were using a 3 cylinder engine and having the ports go to barrels, lucky I read.

Very nice job; the polycarbonate should be fine. I used a 10 mm plate as a viewing hole on a mini hybrid and it held 300 psi in closed chamber testing. Of course this is 'carbonate and thinner and has fail points but should be absolutely fine.

Good luck, keep it rolling.
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Anti blow back system.

Unread postAuthor: Technician1002 » Mon Apr 27, 2009 11:45 am

SubsonicSpud wrote:Look forward to seeing a diagram of the anti blowback system.

SubsonicSpud


Without further adeu;

Features,
gravity feed.
Anti blow back ball trap
Anti double feed ball detent.

As always another quick cheezy sketch. :D
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Attachments
Gravity feed1.jpg
Balls gravity feed in a slightly modified route and drop into barrel as normal.
Gravity feed1.jpg (25.31 KiB) Viewed 1575 times
Gravity double feed detent1.jpg
First ball drops into a depression. The second ball lands on it keeping it there and can't fall off.
Gravity double feed detent1.jpg (28.97 KiB) Viewed 1575 times
Gravity feed fire1.jpg
When fired, the ball collum goes straight up to the new vent at the ball trap. The adjustable trap captures one ball which is in the way of the rest of the balls preventing blow back into the hopper. After the shot, the balls are right there to drop in the barrel for the next shot.
Gravity feed fire1.jpg (29.39 KiB) Viewed 1575 times
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Unread postAuthor: Carlman » Mon Apr 27, 2009 12:11 pm

So its an o ring breach but with a detent...
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Unread postAuthor: covey12 » Mon Apr 27, 2009 1:33 pm

wow thats crazy looking, how do you make those acrylic molds, do you have a computer router or just use hand and power tools?
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Unread postAuthor: VH_man » Mon Apr 27, 2009 1:34 pm

I agree with Covey. If you just made this with a drill press SHARE YOUR SECRET!!!!

I almost want to build another steam engine after seeing this.....
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Unread postAuthor: Technician1002 » Mon Apr 27, 2009 4:52 pm

Carlman wrote:So its an o ring breach but with a detent...


Skip the o ring. :) It's a gravity fed one way check ball trap. Think it will need an O ring? The pocket is to prevent double feeding of bb's in one shot.
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Unread postAuthor: SubsonicSpud » Mon Apr 27, 2009 6:38 pm

Carlman wrote:wow mate just wow, what do you do for a living?


at the moment in between jobs :( did have an offfice job for the last few years.

Technician1002, I like the anti blow back idea, you might need something more substantial than a detent to stop the bbs roling away, a oring may still be a good idea.

inonickname, covey12 & VH_man,

It was actualy pretty simple to make, just took a lot of patience. I don't actualy have a drill press myself, but I used one at a mates house. It was actualy out of true by about 1 or 2 degrees so the holes I was drilling are not perfect. The larger holes in the block were made with a 19mm spade bit, the rest of the holes were drilled out with normal twist drills. A good vise would make it easier but you could just clamp the project to the drill press bench. I also had a spray bottle of water to cool the bits whilst drilling. In total I probably spent about 3-4 hours to produce it.

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Unread postAuthor: sputnick » Mon Apr 27, 2009 6:44 pm

@ technician, I think you are on to something there with your one-way ball thing, seems like a very good idea to me, although it would be somewhat hard to get 100%,

@ subsonic, I'm backing up technician on that one :wink:
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Unread postAuthor: Technician1002 » Mon Apr 27, 2009 7:13 pm

sputnick wrote:@ technician, I think you are on to something there with your one-way ball thing, seems like a very good idea to me, although it would be somewhat hard to get 100%,

@ subsonic, I'm backing up technician on that one :wink:


I doubt it would get 100%. Especially since the ammo is split shot. :)

With recoil, shaking, rapid fire, etc, I can't guarantee 100% on this, but it looks like it is worth a try. I saw the block and thought upscale for a gumball machine gun. A small air cylinder coupled to the 1 inch marshmallow cannon and gumball hopper/feeder and compressor airline for semi auto or full auto. Too many things to try, so little time.

:D Writing my name in a 1/2 inch sheet of plywood with gumballs, priceless. :D
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Unread postAuthor: POLAND_SPUD » Mon Apr 27, 2009 11:37 pm

@tech
nice idea - I was thinking of exatly the same way of preventing double feeding

@subsonicspud is it possible to build it with a drill press from a block of aluminium or brass?
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Unread postAuthor: Technician1002 » Mon Apr 27, 2009 11:49 pm

POLAND_SPUD wrote:@tech
nice idea - I was thinking of exatly the same way of preventing double feeding

@subsonicspud is it possible to build it with a drill press from a block of aluminium or brass?


Part of the reason I drew the ball trap far away from the barrel is;

I was thinking about using the stuck collum of balls to create a high friction pressure gradient. In theory for example if you used 10 bar pressure and had 2 balls between the trap vent and barrel, you would have a gradient of 5 bar on each stuck ball. 5 bar on a loose fit is a lot of blow by. Using a stack of 10 stalled balls on the other hand makes the gradient about 1 bar per ball in the stack, so the blow by would be then limited to 1/5th as much as the first ball by the barrel would only have a 1 bar gradient.

This high restriction to flow means less leakage and more power down the barrel. Think this will help?

I know this is off a lot because air compresses and the above math applies to liquids. It's the concept I am playing with. I'm not an engineer. :(

@Polland Spud.. I'm toying on building it from common PVC T, Pipe, 45, etc for a gumball hopper feed. I gotta work out the lengths so the vertical hopper pushes properly into the side of the T at the ball trap. The ball trap would just be an open 1 inch pipe with a 3/4 inch pipe for the ball plug.

@ Carlman.. So its an o ring breach but with a detent... yep. O rings are a pain to get to work right. They jam, blow out, need replaced, etc. They work better if the muzzle is pointed at the ground where the dent would no longer hold the ball.

Edit.. For steel BB's, a magnet could be used instead of a detent.
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Unread postAuthor: SubsonicSpud » Tue Apr 28, 2009 3:07 am

POLAND_SPUD wrote:@tech
nice idea - I was thinking of exatly the same way of preventing double feeding

@subsonicspud is it possible to build it with a drill press from a block of aluminium or brass?


Yes It would actually be a lot easier to machine, just harder and more time consuming to measure. I did very little measuring on the Acrylic, as I could see where the drill bit was all the time 8) I will probably try to make a more compact high pressure version out of Aluminium at some stage :twisted:


UPDATE!

It works :D

I just screwed the popoff into the back of the QEV housing and gave it some air, haven't even bothered putting gaskets on the backing plate or PFTE tape on the threads :shock:

Here is what I have so far:

Image

And the first test run on video :twisted:

[youtube]http://www.youtube.com/watch?v=D1_ihitIDfI[/youtube]


And look what arrived in the mail today :D :D :D

Image

Lots of 1/4 chrome steel BB's 1080 of them to be precise

Now time to get the barrel and mag working :twisted:

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Unread postAuthor: jackssmirkingrevenge » Thu Apr 30, 2009 2:34 am

n-i-i-i-i-i-ce!

is it just an optical illusion or does the piston barely move?

And yes, finally, decent ammo! You're on to a winner :D

My own barrel and mag setup similar to the parallel design you posted earlier in this thread, as soon as it cures I'll give it a test run :)
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Unread postAuthor: SubsonicSpud » Thu Apr 30, 2009 2:40 am

jackssmirkingrevenge wrote:n-i-i-i-i-i-ce!

is it just an optical illusion or does the piston barely move?

And yes, finally, decent ammo! You're on to a winner :D

My own barrel and mag setup similar to the parallel design you posted earlier in this thread, as soon as it cures I'll give it a test run :)


Yep it is hard to see on the video, it only moves about 2-3mm
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Unread postAuthor: Carlman » Thu Apr 30, 2009 5:28 am

Man that sounds crisp! Cant wait for moar!
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