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Revised automatic mechanism

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Revised automatic mechanism

Unread postAuthor: inonickname » Mon Mar 02, 2009 2:22 am

Well after some revising on my current blowback mechanism, I decided to re design it. It ended up closer to a real blowback mechanism (think uzi, mp40, thompson..)

This design now does not require it to be housed within a tee, and gives a breech mechanism to select the round pre firing, so air wont be wasted in the magazine (also a non airtight magazine can now be used). And more efficiency.

The only real difficulty will be arranging the valve/springs/air pressure so that the bolt will cycle far enough forward to isolate the magazine, far enough back to load another round and have a hard enough spring to open the hammer valve.

I have begun construction on this mechanism, but I do need to get pipe that slides within my barrel (telescoping) and find a suitable bolt and housing.

I'll let the pictures explain it.

Edit: added animation, hopefully it works..

Aww, it's tiny..maybe try zoom it guys
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Attachments
blowback stage 1.PNG
The bolt is returning to the valve now. On the way it selects a round from the magazine and moves it forwards. The bolt is being propelled by a spring, which is not shown in this diagram.
blowback stage 1.PNG (10.49 KiB) Viewed 1273 times
blowback stage 2.PNG
The breech has selected and loaded a round. The bolt has just depressed the hammer valve, allowing a burst of air into the chamber. Air has begun propelling the round.
blowback stage 2.PNG (10.96 KiB) Viewed 1273 times
blowback stage 3.PNG
The bolt is propelled back by the air, and the round is fired. Once it has returned far enough another round from the magazine is selected and the process will repeat.
blowback stage 3.PNG (10.87 KiB) Viewed 1273 times
blowback.gif
Blowback
blowback.gif (10.64 KiB) Viewed 1264 times
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 02, 2009 4:18 am

Looking good if you can make it ;) one thing I'd worry about is the asymetric pressure on the hammer when it hits the valve that might cause jams.
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Unread postAuthor: inonickname » Mon Mar 02, 2009 4:44 am

jackssmirkingrevenge wrote:Looking good if you can make it ;) one thing I'd worry about is the asymetric pressure on the hammer when it hits the valve that might cause jams.


That's a very good point. So, if I centralized the hammer to the piston it would reduce the chance of a jam?

If I can get it moving, I'll be ordering a rifled barrel and some telescoping brass tubes. Very hopefully I can machine the aluminium piston, but I doubt I can get permission to do that from my metals teacher, and machine shops are a rip..

Edit: Darn, I can't find any good suppliers of telescoping brass/aluminium tubing. If anyone could put me on to suppliers for small telescoping tuping I'll scan up my detailed pictures..Fair swap :? Edit: australian, or close to there if possible. Also preferably metric.
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Unread postAuthor: POLAND_SPUD » Mon Mar 02, 2009 4:58 am

I think it doesn't have to be made from aluminium and it doesn't have to be machined

besides you would only need to cut grooves for o-rings so it doesn't require a lot of machining

I suppose that you can do without o-rings... just find a tube and piston that would fit tightly in it... then add some lubcricant
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Unread postAuthor: jackssmirkingrevenge » Mon Mar 02, 2009 6:02 am

inonickname wrote:Darn, I can't find any good suppliers of telescoping brass/aluminium tubing.


Have you tried your local r/c hobby shop?
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Unread postAuthor: Sticky_Tape » Mon Mar 02, 2009 10:33 am

Thought of that but kudos for posting it.
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Unread postAuthor: PaulsAirsoftArmory » Mon Mar 02, 2009 8:14 pm

From what I understand, the technical name for your design is an "open-bolt" design, where the bolt is held back until the trigger is pulled. Then the bolt would go forward and fire the round.

The only problem I can see with your design is that I am unsure if the bolt would fully return after each shot, otherwise all the air would just go out of the barrel.

But I have already thought up a solution for this-2 separate air chambers. One that would be connected to a set of telescoping metal tubes connected to a valve. One of those tubes is connected to the barrel that would provide a power source for the projectile, and the other of the two tubes connected to some sort of valve as in your design. There would also be a second set of telescoping tubes. One would be connected directly to the bolt and the other to a valve parallel to the first valve that would be triggered simultaneously, and at the same time connected to a separate air source. When the valve is released, the tube is pressurized and the pressure forces the bolt back to a point where the air can escape through a hole in one of the tubes.

It seems complicated, but I am a visual thinker and I can picture it perfectly in my head, but I am a horrible artist, so I have no good way to show you. I think that this will work perfectly if done properly and would even be able to fire in fully automatic mode it it works. I may have to build a prototype of this for myself.
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Unread postAuthor: jackssmirkingrevenge » Tue Mar 03, 2009 1:20 am

PaulsAirsoftArmory wrote: The only problem I can see with your design is that I am unsure if the bolt would fully return after each shot, otherwise all the air would just go out of the barrel.


Technically the air cannot escape until the bolt is out of its housing, at which point the chamber empties through the barrel and the piston can return.

I am a horrible artist, so I have no good way to show you.


If you're not familiar with computer based drawing programs you can easily make a pencil sketch and scan/take a photo of it, even the most horrible of diagrams will convey your idea much better than a written description, especially when you consider that more than half this forum is populated by ADHD suffering adolescents ;)
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Unread postAuthor: PaulsAirsoftArmory » Tue Mar 03, 2009 7:23 pm

I kept thinking about it and I came up with a completely new design last night that I have already designed in Paint, and I was going to make a new topic about it sometime tonight, although it is very different than this design. I will try to make another design illustrating my thoughts previously posted tonight as well, and then I will post it here.
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Unread postAuthor: PaulsAirsoftArmory » Tue Mar 03, 2009 8:37 pm

I now have a post up showing my new design. I will try to get a visual design of my above thoughts on here later tonight.
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Unread postAuthor: roboman » Sun Mar 08, 2009 11:25 am

But I have already thought up a solution for this-2 separate air chambers. One that would be connected to a set of telescoping metal tubes connected to a valve. One of those tubes is connected to the barrel that would provide a power source for the projectile, and the other of the two tubes connected to some sort of valve as in your design. There would also be a second set of telescoping tubes. One would be connected directly to the bolt and the other to a valve parallel to the first valve that would be triggered simultaneously, and at the same time connected to a separate air source. When the valve is released, the tube is pressurized and the pressure forces the bolt back to a point where the air can escape through a hole in one of the tubes.


From what I can tell, you're describing
this.
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Unread postAuthor: PaulsAirsoftArmory » Sun Mar 08, 2009 7:03 pm

Yes, very similar to that, but a double valve instead of that awesome combined valve like in that animation.
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