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full auto electric drive revisited

A place to ask general spud cannon related questions.
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 9:51 am

POLAND_SPUD wrote:A cylinder or syringe that uses the pressure inside the chamber to load an ammo and move the bolt forward (to firing position). When the gun fires pressure inside the chamber falls and the bolt is pulled by a spring backwards to take next ammo. When the pressure inside the chamber rises the cylinder pushes the bolt forward and the gun is ready to fire again.


If I understood correctly, the bolt movment would be similar to
this design which al-xg had proposed some time ago, it would be a much more reliable system than the one I've designed to be honest.
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Unread postAuthor: POLAND_SPUD » Fri Nov 30, 2007 10:14 am

yes basically the same principle. The difference is that my design most likely has to be limited to semiauto and requires a QEV (as a main valve) triggered by a sleeve valve - to make sure that there is enough time for the bolt to be pulled backward before the pressure inside the chamber would rise and push the piston and the bolt forward.... A thin copper pipe or an air hose could be used to connect the chamber with the cylinder making the whole thing less complicated and easier to make than al-xg's design...
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 02, 2007 11:28 am

Well, I've made a very basic prototype of sorts. I'm aware that it's as ghetto as they come but I've never been the neatest of fabricators, and when it comes to prototyping function over form is the definite rule :)

The power is certainly there, it will send a 0.22 airgun pellet through both sides of a soup tin at 100 psi. It does leak a little in the "closed" position, but at acceptable levels as far as I'm concerned. As to this being "blowback" on its own accord, perish the thought - I fired about 10 test shots and not once did the bolt show any inclination to move back.

This means that some form of external power is in order, so it's either an electric motor driving an eccentric cam, or a pneumatic piston to keep the system "air only", which is preferable in terms of convenience but would divert precious air away from its function of propelling the projectiles down the barrel - so it'll probably be electric.

Watch this space :)
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Attachments
blowbackproto3.jpg
bolt removed
blowbackproto2.jpg
rubberband removed, bolt in the "closed" position (with breech access to the magazine open)
blowbackproto1.jpg
The prototype in all its ghettoness. The rubber band is just a temporary measure, the real deal should have a tension spring (or two ;D) - bolt is shown in the "open" position (with breech access to the magazine closed) - the duct tape is there as an improvised "bolt stop" to prevent the bolt from going too far into the barrel.
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Unread postAuthor: POLAND_SPUD » Sun Dec 02, 2007 1:49 pm

jackssmirkingrevenge wrote: I fired about 10 test shots and not once did the bolt show any inclination to move back.


Ohhh that's suprising.... maybe the rubber band is to strong or the pressure is too low...?

anyway, it looks nice :)
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 02, 2007 11:03 pm

Well, I only have 110 psi max on tap and the rubberband is just strong enough to overcome the friction. In order to be successful as a blowback I'd have to sand down the bolt to a smaller diameter so it's a looser fit, to cut down on friction, but that way it would leak too much to be viable - so it looks like the electric route is the best idea.
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Unread postAuthor: windshrike » Sun Dec 02, 2007 11:10 pm

I like the design, amazing work(just like evrything else that pops out of your head!) and I was wondering, could you hook this up to a small reservoir of air(NOT an HPA or CO2 tank, just a small reservoir) andsee how long it will fire? :wink:

Also, I do see the drawback that electricity must be applied to keep the gun from firing, as a loose connection could cause an accident. :shock:

But again, I applaud you :P .
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Unread postAuthor: jackssmirkingrevenge » Sun Dec 02, 2007 11:25 pm

I doubt it would fire for very long, the intention of this project was always to have it hooked up to a large volume compressor tank and as such, having a separate wire to power a motor isn't that much of an extra burden.

Also, I do see the drawback that electricity must be applied to keep the gun from firing, as a loose connection could cause an accident.


I doubt this will be an issue since the intention is to open the airflow only when firing is necessary.
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Unread postAuthor: POLAND_SPUD » Mon Dec 03, 2007 2:06 pm

It's a pity it has to use external power - I liked simplicity of this design....
I suppose it would work better with greater caliber (greater bolt surface) but i understand that scaling it up would make everything more air consuming and difficult.
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Unread postAuthor: iknowmy3tables » Mon Dec 03, 2007 3:17 pm

no no no the whole electric crap is just annoying to have to add on, just give it lube, lighten the rubber band, lighten the bolt's mass, and if you must; make part of the bolt diameter wider to absorb more force. paintball guns like the auto cocker can use the blow back force to load the ball, and even cock the hammer for the valve. you have to be able to get the blowback force to at least push the bolt
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Unread postAuthor: VH_man » Mon Dec 03, 2007 4:28 pm

Do you have a video of your prototype firing without any motor attached? i feel like this would work quite well.

i think that one way you could make this electronic but not overly-insane would be to run some sort of oscillation circuit to the solenoid.

that way, you press a button, and your solenoid gives a RATATATATA, and all you have to worry aobut then is a blow-foward system. plus, its extremely air efficient.

i am currently working on(with other things) a 6mm full-auto system that mimicks the mechanism found in my GBB airsoft Mac-11. I will post diagrams sometime, its fairly simple, and requires no electronics. and best of all, if i build it right it should give a fairly large amount of kick........

anyway, i love how all the things you make that look gosh darn beautiful dont work the way you want them to. Im interested to see how this one goes though.
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 03, 2007 4:58 pm

I would have liked to avoid incorporating electrics, in another thread I suggested this idea to make it work better as a pure blowback breech:

Image

Looks like that even due to overwhelming public demand, I'm going to have to give it a go :roll: patience my friends, in the winter months epoxy takes twice the time to set :cry:
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Unread postAuthor: F.E.A.R._Sniper » Thu Dec 20, 2007 6:40 pm

iknowmy3tables wrote:I really don't like this no rubber seal thing the leaking air might blow the bbs from the breech, I think you just got to cope with the friction I think basic solinoids just aren't fit for this job especially if its homemade, get something stronger


Or he could use delrin to build everything as it is a self lubricating polymer that doesn't require o-rings to make a seal, so he wouldn't have to worry about the o-rings adding extra drag on the bolt or anything
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Unread postAuthor: jackssmirkingrevenge » Fri Dec 21, 2007 12:22 am

Or he could use delrin to build everything


... in an ideal world, but sadly I don't have a lathe so I'm stuck with epoxy casting.
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Unread postAuthor: Antonio » Wed Mar 26, 2008 10:14 am

looks pretty cool. I am trying to go back to this mag valve system as its so small and simple. What are you using as a seal? Do you have any pictures of that?
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Unread postAuthor: jackssmirkingrevenge » Wed Mar 26, 2008 10:15 am

Seal at which point?
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