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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 » Wed Nov 28, 2007 4:15 pm

Really it is just the opposite of your blow forward breech prototype.


precisely what I was thinking, if i don't need a motor then all the better. I started the first casting (it has to be done in two parts), watch this space.
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Unread postAuthor: Hawkeye » Wed Nov 28, 2007 4:33 pm

I can see it fitting in a design like the Beretta Sub-Machine gun.
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 28, 2007 5:11 pm

Assuming it works, hooked up to a regulated co2 or hpa supply it would make a neat submachinegun, but since I don't have access to such a setup the plan is to incorporate it into a long barrelled M60 type device that would hook up to a compressor, something I've wanted to make for years.

With 110 psi and the barrel I'm using hooked up to a blowgun, I can put a 0.22 pellet through the bottom of a soup tin. If I can get that sort of performance at 2-4 rounds per second I'd be a happy bunny :)
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Unread postAuthor: iknowmy3tables » Wed Nov 28, 2007 6:17 pm

I don't get it is it or is it not acting as a valve, why does the solenoid need to be there
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Unread postAuthor: jackssmirkingrevenge » Wed Nov 28, 2007 11:29 pm

Technically, when you let the air in it should push the projectile out of the barrel and also push the bolt back. I doubt it there will be enough energy to push the bolt back enough to cycle the action, which is why my plan includes some sort of electric drive that will do the job. However, pending on friction and spring strength, it might not be necessary.

edit: this is what the mechanism should look like in action, for simplicity's sake the spring has been replaced by a rubber band for the animation.
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Unread postAuthor: Hawkeye » Thu Nov 29, 2007 9:03 am

I still say balance the spring tension. Put a band on either side if you don't want to back it up with a spring.
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Unread postAuthor: CpTn_lAw » Thu Nov 29, 2007 9:22 am

...there is something that kinda gets my attention...when you actually get it to shoot, the air instantly pushes the piston back. so, the projectile stops accelerating while still in the barrel. What i'd recommend is you use a small captor, that opens the solenoid when the projectile passes next to it, thus allowing more air to be used to propel du projectile.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 29, 2007 10:06 am

Hawkeye wrote:I still say balance the spring tension. Put a band on either side if you don't want to back it up with a spring.


I'll go with one spring first, if the friction is significant I'll add another one.

when you actually get it to shoot, the air instantly pushes the piston back. so, the projectile stops accelerating while still in the barrel.


The projectile and the bolt both have the same force of air acting on them, however you have to consider that the projectile is small and light, while the bolt is heavier and also is being held by the spring - this means the bolt will accelerate slower and hopefully give the projectile enough time to leave the barrel before closing off the air. This is similar in concept to how blowback pistols and submachineguns work.

The advantage of this design over the blow forward experiment is that the spring is out in the open so I can easily play with different tensions to fire tun the mechanism.
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Unread postAuthor: Hawkeye » Thu Nov 29, 2007 10:25 am

Jack, I thought the Epoxy block would be of a similar size to the interior diameter of the pvc you typically use for your chambers. Does that not come in lengths with threaded ends capable of being capped? I thought a piece with a cap would allow easy access to a spring behind the mechanism. You could also bore a hole in a cap and run a bolt for adjusting tension through that.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 29, 2007 10:55 am

You mean using a compression spring like my cartridge fed pneumatic? It would work, but I'm going to give tension springs a go first, more compact :)
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Unread postAuthor: iknowmy3tables » Thu Nov 29, 2007 6:54 pm

now your talkin
if you want more force on the bolt for blow back just give it more suface area or increase the size of the bolt
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 29, 2007 11:02 pm

i'm building it as per the diagram for now, I'll try and "tune" it by playing with the spring strength and preload.
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Unread postAuthor: LikimysCrotchus5 » Fri Nov 30, 2007 12:22 am

Just a thought, would you need to put some sort of bumper between the outside part of the bolt where the spring is where the T part of the bolt contacts the gun. If the force was large enough, maybe you would but you this bumper could possibly help the cycle action to continue on its own. If it was some sort of rubber that would give a nice ricotcheing force, then this cycle action maybe possible without a solenoid valve thingy.

i just had to be all smart and then you the word "thingy" :roll:
Lol i crack me up :D
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Unread postAuthor: jackssmirkingrevenge » Fri Nov 30, 2007 12:23 am

Naturally, some form of bumper to stop the bolt from flying out completely would be in order, pending how much force is actually going to be on it.
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Unread postAuthor: POLAND_SPUD » Fri Nov 30, 2007 9:44 am

I have an idea that is very simmilar to your design the difference is that the spring is used to pull the bolt in order to load new ammo and insted of an electric drive a piston powered by air from the chamber is used to hold it in forward position.

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.


would this work ? (assuming you can understand what I mean :D )
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