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Airsoft Mini-Gun

This area is for the discussion of BB or airsoft sub machine guns, and or other small arms such as pellets.
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Airsoft Mini-Gun

Unread postAuthor: cfunkrun » Thu Feb 19, 2009 1:21 am

Alright, I'm floating around the idea of making my own airsoft Mini-Gun out of mostly readily available items such as PVC pipe and copper tubing.

I'm trying to figure out all the parts i need, before i set off building anything, and tossing a few ideas around. I'm gonna make the barrels spin and regulate pressurized air-bursts for propulsion using an electric motor, gearing, and a battery.

I'm planning on using pressurized air for both the propulsion of 6mm plastic BB's, and hopefully for ammunition feeding. (right now, im not expecting the prototype to be man-portable, i'll have it connected to a shop compressor and car battery, and set it up on a table or mount).

To control the air bursts for propulsion, i have this idea for a rotary valve with a pressure chamber. The size of this chamber should influence directly how much air, up to a point, will be released upon each pressure-release cycle.

Here's how my idea works. There is a large circular tube, with 3 pipes coming out. Bottom pipe is air intake (A). Left pipe leads to the pressure chamber. Top pipe leads to the barrel, or breach or wherever you desire the air to go (B). The dark blue area is a solid cylinder shape, made of aluminum or something, and fits airtight in the larger tube (obviously not like this illustration, spaced for clarity purposes). The tube is capped off on both sides, with a hole in the middle for a rod attached to the inner cylinder to rotate it in the tube. There are hollow places drilled into the cylinder to create a 90 degree "pipe" through it.

When the pipe aligns with the intake and chamber, the pressure chamber will be pressurized.

When the cylinder is rotated by 90 degrees, the pressure will release out the upper pipe as the "pipe" drilled out of the cylinder aligns with the pressure chamber and the air exit.

The cylinder will rotate 180 degrees more, back to where it started, restarting the cycle.

I imagine the internal parts of this valve would need a bit of lubrication, as to prevent leak-causing parts wearing, and to help seal off leaks.

Does anyone out there think this will work?

If anyone wants to go try this, by all means go right ahead, and tell me the results.
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Rotary valve to create a burst of air, once per revolution of the central cylinder.
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Unread postAuthor: starman » Thu Feb 19, 2009 1:52 am

The concept may have some potential, but I think you'll have better success if you have a stepper motor that steps from one position or the other instead of just "flying by" in an unstopping rotation. I could see potentially using an RC servo motor.
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Unread postAuthor: inonickname » Thu Feb 19, 2009 2:42 am

I've posted the exact same design, except it's easier to build....

Welcome to spudfiles, good luck if you decide to build it.
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 19, 2009 3:03 am

I used to love that webcomic, though I can't for the life of me remember the title.
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Unread postAuthor: Ragnarok » Thu Feb 19, 2009 3:22 am

jackssmirkingrevenge wrote:I used to love that webcomic, though I can't for the life of me remember the title.

Gone with the Blastwave?
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Unread postAuthor: jackssmirkingrevenge » Thu Feb 19, 2009 3:46 am



That's the one :)
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Unread postAuthor: cfunkrun » Thu Feb 19, 2009 12:36 pm

The concept may have some potential, but I think you'll have better success if you have a stepper motor that steps from one position or the other instead of just "flying by" in an unstopping rotation. I could see potentially using an RC servo motor.


Yeah, but i want the release of air to be exactly synchronized with the rotation of the barrel, and i figure using the existing motor will make it easier. Using another motor would be quite difficult to time with the rotation of the main motor, so i figured just run a gear box to get 6 releases of the valve for every turn of the barrel carriage. (6 barrels)

I used to love that webcomic, though I can't for the life of me remember the title.


Haha I loved that web comic, but haven't caught up with it, a long while back the author was leaving for the army or something.

inonickname, i think i understand your concept there. There's as many holes in your rotating piece of tubing as there are barrels, which align to one hole in the inner tube, which the top barrel will fire when the holes align. Looks far more efficient then my idea. I'll study that design a bit more.

Also, i had a couple other ideas here.

Both use the concept of a housed piston blocking a hole in a tube, housed within another tube.

The first image, uses an arm that is attached to a spinning wheel (green) offset from the middle of the wheel, which then moves the piston back and forth, blocking or releasing air (i don't think the spring is necessary in the first image). It works essentially like the inside of a gas engine.

Second image, same idea, but instead of an arm, the wheel has a small cylinder shape sticking out of it offset from center, and the wheel is set a little bit above the piston arm. when the wheel comes around, the cylinder will press against the arm, and when the cylinder spins to far above the rod, will let go of it and the valve shuts.

I made a prototype of the 2nd solution out of Meccano (lol) by attaching a spring to a rod ( simulates piston + spring + rod ) and adding a round knob off a gear attached to a spinning motor. when the knob lines up with the rod, it'll push it forward. when the knob lets go, the rod springs back.

It worked well using the relatively slow speed of the small motor, but i haven't test it using the high speed of a faster motor. I can imagine vibration, and part breakdown could be big factors with that design. Since the wheel wouldn't be balanced properly, the mechanism would probably shake itself apart. I added counterweight to the other end of the wheel, which improved vibrations, but it would require a lot of tweaking.

What you guys think?
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Unread postAuthor: psycix » Thu Feb 19, 2009 1:28 pm

I'd use hammer valves if I would build one.
Simply let the hammers be pushed open on certain parts of the rotation by placing sloped obstructions.
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Unread postAuthor: john bunsenburner » Thu Feb 19, 2009 1:33 pm

If i understand correctly ou are trying to build a auto gun, but really your plans are very complicated, are you building this to be practical or for sh*ts and giggles, if not latter then i suggest you try a vortex or cloud, if latter then keep it up, this seems like something interesting, and i agree to psycix, you shoudl rather use a hammer valv eover your current idea, which will be extremely difficult to build and get to work.
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Unread postAuthor: cfunkrun » Thu Feb 19, 2009 1:54 pm

Yeah, basically seeing if it can be done, may as well start something that seems like a challenge. if it works flawless, then awesome, Bonus!

If it doesn't work, i'll build down simpler until i get results.

Yeah, i know i work backwards, but that's how i prefer to work sometimes. :wink:

And if anything, maybe some people can use some concepts and ideas, and improve on them for their own projects. Then i would be happy enough just thinking that i would have contributed a small amount to something that someone would actually get working. :P

(EDIT)

Alright, I thought about hammer valves. I drew out a couple of them.

- Red is moving valve parts.
- Yellow is a seal (O-ring).
- Blue is air flow.

First design i made up off the top of my head. Issue with that one is that there would either be too much air leakage, or too much friction (making it airtight leans towards high friction to move it, making it move freely leans towards more air leakage).

Second design, i looked up simple hammer valves, this one seems to be airtight and reliable, but since air pressure is keeping it sealed closed, it may not be easy to open. But if the motor has enough torque, it shouldn't be a problem to drive the barrels and that valve.

If anyone knows an airtight, easy-moving hammer valve design, could you point me in the right direction? :P
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2 hammer valve designs
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Unread postAuthor: psycix » Fri Feb 20, 2009 4:31 pm

Those two designs are the most common.
The top one needs at least 3 o-rings while the lower one just needs some sort of sealing face.
The top one, however, is in equilibrium of force and does not need alot of force to open, like the bottom one.
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