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PVC + Delrin piston valve cannon (picture heavy)

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: Crna Legija » Thu May 24, 2012 2:35 am

Desmo wrote:Ill try find it on ebay tommorow for you. And yeah you do if you want to use the TIG. The bottle costs $300 outright or its about $90 rental per year then its $90 to fill roughly. A fill goes for about a year with the amount of stuff i do. , the plasma needs a compressor to go with it.



ah cool, i could probably ''borrow'' a 10 cubic meter tank from work that would last a bit.
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Unread postAuthor: Desmo » Thu May 24, 2012 9:06 am

That'd do it :) Will drop you a message tommorow bout that welder too. totally forgot tonight haha.

Okay so wont get much time to tinker over the next week so here's a few design changes that will happen once a bit of time makes itself available.

Need to go grab some more delrin and remake the end cap with the QDV pilot built into it. Dealing with all the leaks of the current version is annoying as hell and this way it'll have a dead minimum of pilot volume. The schrader valve for the compressor will get built into it too.

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Also need to laser cut some supports as well as mount the compressor/battery to it somewhere and make it all look good. Found a car boot solenoid too that will hook up to the qdv to pop it open remotely. So i dont have to be near the thing :lol: Then it's done! Time to move onto something more serious :shock:

BTW, What are your thoughts on the use of a schrader built into the piston as a check valve? Would it work or does the pin physically need to be depressed to open one. Kinda hoping pressure alone is enough to unseat it. Haven't got one around to test!
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Unread postAuthor: jakethebeast » Thu May 24, 2012 9:41 am

Hmm, if i remeber correctly, schrader valde should "pop" open at around 55psi
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Unread postAuthor: jackssmirkingrevenge » Thu May 24, 2012 10:06 am

Desmo wrote:What are your thoughts on the use of a schrader built into the piston as a check valve? Would it work or does the pin physically need to be depressed to open one. Kinda hoping pressure alone is enough to unseat it. Haven't got one around to test!


As jake said it's around 50-70psi repending on brand.

Since you have a lathe though, you would be much better off simply making a floating o-ring seal, nothing to it.

http://www.spudfiles.com/forums/premade ... 23636.html
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Unread postAuthor: Desmo » Thu May 31, 2012 3:44 am

Cheers for the advice dudes ^^

Alrighty, Had a day off today so a few things got finished before the big testing weekend. Main job was to sort out that leaky QDV pilot valve.

Those plastic taper thread end caps appear to be the most non airtight devices ever conceived, so a metal bung was needed to seal it up for good. I'd already bought a 1/4BSP tap but only found out after using it that it's a taper tap not a straight through one, and at $23 a shot wasn't prepared to get another one.

So doing what any dodgy back yard engineer would do, a quick disconnect was gutted, cut apart and welded in to make a $4 threaded bung. Works great too!

If you ever wanted to see the inside of a QD nitto style fitting... Quite ingenious with the floating seal. If the spring was taken out, i wonder if you could make one into a little piston valve?

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But anyway, The bottom was cut off, and lathed down to press fit into the top of the QDV body, the faux-chrome was ground off and the thing welded in albeit hideously lol. No doubt, chinese fittings and chinese made galvanised pipe was never made to be fused. But too bad! :P Black paint covers all sins... >.>

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Added bonus in that the bung takes up heaps of pilot volume inside the qdv inlet. Never a bad thing. After that the end cap needed a little chunk milled out of it so the bung wouldnt rub on it. Easy done.

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The valve work all ready to go.

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Works much better again then it has before. And no more leaks. Can't complain about that :) Only problem is the spool doesn't seem to open completely when its fired, even though the time from opening the qdv to the cannon firing is next to nothing.

That would be because I'm a retard and didn't put any vent holes before hind the spool. So it would quickly open then rebound again. Quickly sorted that one out with some 2mm holes drilled in the back of the valve body.

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I'll test it tommorow but fingers crossed it slams open and stays that way. Not sure what it would be if this doesn't sort it considering the spool moves super freely. Perhaps without a projectile there's no real force to push the spool open?

But after that not much else to do with this toy. Going to 3d print a muzzle brake and attach all the compressor/battery/brace stuff and machine that new rear plug when the delrin comes and that's this project done with. I might toy around with surface casting hollow pistons to see what effect reducing the weight to extreme levels has on performance, but that'll be it.

Have to think about what to make next. I'm thinking of finishing the QDV metal cannon and firing that at as high a pressure as the brushless compressor will pump it up to (500-600psi hopefully). That should be a super quick build.

Definitely need to make a hybrid too. My friend wants to make a "deiseling" cannon that uses two co ax chambers, with a pilot valve in the outer one firing a metal ring down the inner co ax chamber @ ~1000psi to compress and combust a mixture that will fire the projectile out via a burst disk. Sounds cool enough to at least attempt as a partnership :)

Grabbed some 65mm diameter bright steel rod for my own hybrid burst disk cannon. I reckon a straight copy of this cannon (http://www.spudfiles.com/forums/lardas- ... 15524.html) will be a good starting point, given its fairly easy to machine and super over built.

That's it for now. Definitely a few damage videos on the way 8)
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Unread postAuthor: jackssmirkingrevenge » Thu May 31, 2012 11:50 am

My friend wants to make a "deiseling" cannon that uses two co ax chambers, with a pilot valve in the outer one firing a metal ring down the inner co ax chamber @ ~1000psi to compress and combust a mixture that will fire the projectile out via a burst disk. Sounds cool enough to at least attempt as a partnership


Essentially that would just be an overcomplicated hybrid though, while admittedly benefitting from compression heating.

If you're going down that route, you might want to consider a hybrid cannon driving a piston that will power a light gas gun ;)

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Unread postAuthor: mattyzip77 » Thu May 31, 2012 11:57 am

Very, very nice indeed! Looks like some of the senior members have some competition finally!! 8)
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Unread postAuthor: jackssmirkingrevenge » Thu May 31, 2012 12:22 pm

mattyzip77 wrote:Looks like some of the senior members have some competition finally!! 8)


It's all about construction techniques and their application. It's all well and good to come up with new concepts, but if you can't flesh them out, you're stuck with just an idea.

If you're going to stick with standard fittings, there's only so much you can do on a reasonable budget, so most launchers will end up looking pretty similar. Machine tools open up a whole new world of possibilities, but understandably few can afford to spare the cash. In some notable cases (like some of the younger members on this forum) this drives innovation up a notch and outstanding launchers appear. That's one of the reasons I really like this forum :)
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Unread postAuthor: Desmo » Thu May 31, 2012 12:27 pm

jackssmirkingrevenge wrote:
My friend wants to make a "deiseling" cannon that uses two co ax chambers, with a pilot valve in the outer one firing a metal ring down the inner co ax chamber @ ~1000psi to compress and combust a mixture that will fire the projectile out via a burst disk. Sounds cool enough to at least attempt as a partnership


Essentially that would just be an overcomplicated hybrid though, while admittedly benefitting from compression heating.

If you're going down that route, you might want to consider a hybrid cannon driving a piston that will power a light gas gun ;)

Image


its basically a coax light gas gun :). With the hybrid stage replaced with co2 judging by that diagram. Having a high mix hybrid in the first stage would be crazy hard to machine me thinks. Probably a bit easier to tweak it with pneumatics firing the "piston" in that diagram anyway. Lots more research to do on that subject none the less.
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Unread postAuthor: jackssmirkingrevenge » Thu May 31, 2012 2:02 pm

CO<sub>2</sub> is a bad idea because of its density, you're better off using HPA or Nitrogen, or since you need helium (hydrogen = kaboom) for the light gas stage anyway, use compressed helium as a piston driver. Lighter gas = better performance.
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Unread postAuthor: POLAND_SPUD » Thu May 31, 2012 3:00 pm

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Unread postAuthor: jackssmirkingrevenge » Thu May 31, 2012 3:06 pm

I was about to say... a straight hybrid is a better idea :)
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Unread postAuthor: jakethebeast » Thu May 31, 2012 3:40 pm

Ill double that JSR :wink:


But DUDE, nice welding!! :shock:
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Unread postAuthor: Desmo » Fri Jun 15, 2012 6:39 am

Well disappointingly my delrin never arrived so i didn't get the chance to redo the end cap. So i will have to order that elsewhere :(

Though that's given me a chance to think things over and in my estimation it seems that a QDV without any kind of restriction on the other end (projectile, barrel etc) doesn't appear to work as it should. It does self actuate, but only about halfway. Whether that's down to the port geometry i used, ratio of the pilot volume to piston size whatever, it doesn't work lol :P

SO when the delrin does come ill make a big slide valve so it can be semi auto. should be plenty simple to construct and offer more flow as a pilot valve.

In the mean time i busted out some supports from pine (Think it was pine, just grabbed whatever was around heh). I'm going for a bit of an artillery piece look to it, seems to suit quite well. What do you reckon? :)

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As for bigger cannons a friend who repairs appliances saved a few compressors for me. So high pressure pneumatics are a go :) Something fully automatic at ~500psi sounds appealing. :wink:
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Unread postAuthor: mattyzip77 » Fri Jun 15, 2012 10:53 am

It looks good man, but you need to give it a paint job. Maybe a camo green flat I'm thinking. Very nice job on the supports. You are really a skilled craftsman if I do say so myself!! How do you plan to load the ammo for the semi auto??
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