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Spinning Bolt

A place to ask general spud cannon related questions.
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Spinning Bolt

Unread postAuthor: Flash » Sat Apr 12, 2008 1:39 pm

Here's a little design I came up with just a now. Its basically a bolt that spins to close the breach instead of pushing a painball into a barrel to seal the breach. It should save space and opens up the possibility of a building an automatic paintball marker with an insanely high ROF. In theory all it would need to function is a simple open/ close valve and a continuous air source.

Image

I haven't really spent the time to sort out all the problems yet, but I though it was an interesting concept.

Potential Problems:
  • I can't figure out a way to make it spin (besides using a propeller)
  • I don't know how to make it so it fires only when the breach is completely closed
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Unread postAuthor: judgment_arms » Sat Apr 12, 2008 1:45 pm

I had I similar idea, only the piece the spun was on the outside.
It was going to be a chain gun (uses a motor to operate the mechanism), so the same thing the spun the breach opened and closed the main valve.

I scraped it, deciding that I did not want an extra mechanism to feed…
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Unread postAuthor: jrrdw » Sat Apr 12, 2008 1:58 pm

I was thinking of a simular type valve driven by a eletric motor. Another problem is the feed, with a fast turning valve/breech/bolt, how will you keep from cutting the paint balls in half?

I was thinking a soft/rounded catch at the bottom that the ammo could land on and push down allowing the valve to turn closed, then when fired, trips another catch allowing the valve to open and reload.

I haven't thought it through though.
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Unread postAuthor: psycix » Sat Apr 12, 2008 4:35 pm

Hmmm never thought about a spinning bolt.
Not a bad idea actually!
Though how will you seal the sides when the bolt is closed?
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Unread postAuthor: judgment_arms » Sat Apr 12, 2008 7:52 pm

100% seal is not necessary, though if you used o-rings they’d work like bearings.
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Unread postAuthor: jrrdw » Sat Apr 12, 2008 8:25 pm

Cut two rings of a larger diameter pvc pipe one for each end of the bolt, groove the inside of the chamber to match, greese it up. That would give in hinges? to rotate on and hold it in place.
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Unread postAuthor: Flash » Sun Apr 13, 2008 10:39 pm

Thanks for the idea about the electric motor. I changed the design to show what it might look like if it had one. I also came up with a way to cut off air when the bolt closes.

Image

I'm not too worried about the bolt chopping paint because if I ever do make this thing, I'll be using reballs so I can use it inside my house.

Now that I know how to rotate the bolt and time the air release, I just need to figure out a way have the motor turn the bolt 180 degrees with every trigger pull. :?

BTW: WTF kind of smilie is this :sign4: ?
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Unread postAuthor: judgment_arms » Sun Apr 13, 2008 11:04 pm

Flash wrote:BTW: WTF kind of smilie is this :sign4: ?


One that you can eat!
Great, now I want some Spam, the wonderful, barely edible, meat in a can! :D

:spam1:

Sorry I'm tired....
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Unread postAuthor: rp181 » Sun Apr 13, 2008 11:18 pm

you could use a stepper motor, but those are hard to control without an IC.
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 14, 2008 12:29 am

*cough cough*

:P :wink:

In terms of geometry, it's a much better idea to have the bolt spinning on an axis perpendicular to the barrel, as opposed to coaxially as in my prototype.

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Unread postAuthor: SPG » Mon Apr 14, 2008 11:50 am

"Cough, Cough, Cough"

"Cough, Cough, Cough, Cough"

Image

At the time I said this:

This is just about as simple as I can get on electric bbmgs. I reckon a CO2 tyre filler would work fine and it would then have a "safety" gas valve, with this. A speed control would provide variable rate of fire, and a simple bit of circuitry on the back of the motot could make sure that the barrel always stopped in the AIR CLOSED position. I think possibly two o-rings on the barrel one on either side of the inlets and some grease, and we'll be away. It might need a barrel shroud and a bearing near the muzzle as any curvature in the barrel would make it oscillate, which could give you an interesting spread pattern.

Pros
Very simple
Rate of fire control
No wasted gas

Cons
Fine tolerances
Needs batteries
At very high ROF the power will drop due to insufficient gas entering the barrel
(GGDT gives a power drop if the valve is open for less than 4 milliseconds with a 24 inch barrel)


And I even built one - and it leaked like a seive (but then I didn't know what I know now) and GGDT lied.

Go for it I say, like I said we've moved on a lot since that post, and I reckon it's very do-able.
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Unread postAuthor: Flash » Mon Apr 14, 2008 11:14 pm

AWW! It seems like every time I think I come up with some great idea, someone else beat me to it. :x

SPG wrote:Cons
[1]Fine tolerances
[2]Needs batteries
[3]At very high ROF the power will drop due to insufficient gas entering the barrel

And I even built one - and it leaked like a seive (but then I didn't know what I know now) and GGDT lied.

Go for it I say, like I said we've moved on a lot since that post, and I reckon it's very do-able.


1. I think I can fix that with some parts from Mcmaster, they have polyester tubing in various diamters. I can also throw in a couple o-rings to fix any seals

2. I don't know much about motors (its on my list to wikipedia), but I hoping that a simple 9 volt will give it enough juice.

3. I was thinking about using that space that controls when the gas is allowed to flow through the bolt as a firing chamber. This should increase the flow.

I'm also planning on designing a valve that cuts off air the chamber when the trigger is pulled

You said you built one? Did you have any problems with it jamming? The more I think about it, the bigger the problem becomes, especially with paintball size rounds.

jackssmirkingrevenge wrote:In terms of geometry, it's a much better idea to have the bolt spinning on an axis perpendicular to the barrel, as opposed to coaxially as in my prototype.

Why is it better to have it spin perpendicular to the barrel?

After reading yours and SPG's topics, it seems like the biggest problem with these things is just the seal. I'm definately using real o-rings for the rotating valve, but what do you guys think about making the actual bolt out of a slightly stiff foam or a semi-hard rubber? I would have to sacrifice some of the ROF, but thats the only way I can think of to seal the entire breach.
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Unread postAuthor: jackssmirkingrevenge » Tue Apr 15, 2008 12:35 am



throat pastille? You're mentioned in my thread ;p

Why is it better to have it spin perpendicular to the barrel?


To minimise air losses, if you compare both systems perpendicular seems to be the better option.
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Unread postAuthor: SPG » Tue Apr 15, 2008 6:52 am

jackssmirkingrevenge wrote:


throat pastille? You're mentioned in my thread


No, but I gave up smoking last week and seem to have developped a smoker's cough since, I'm probably purging all that tar.

Overnight thought on this would be the addition of a "hammer valve" with a lobe on the barrel to trigger it with each rotation. Could be as simple a modified schaeder valve. It would solve the leak problems which are really only an issue when the gun is at rest, as when it's spinning the propellant gas can "leak" down the barrel.


EDIT: Re. Jamming. No it didn't jam, but the problem is that if the barrel is rotating too fast the BB (because I was using BBs) just didn't feed at all, it would "bounce" from the edge of the hole a bit like a poorly aimed pool ball. If it got more than half way in though then it'd get all the way in and not jam. An obviously solution to this would be a "feed ramp" rather than a straight hole so that your projectiles were pushed into the barrel. Or slow down the rate of fire of course. I'd always thought about using one of the speed controllers from my old Scalectrix (slot car racer) as that way I could vary the ROF depending on the trigger pull.

I think though like a lot of things in the micro-spudgun world the key is high and constant pressure, so regulated, or even unregulated CO2 would have been the way to go.

If I were doing it again, and I might give it a try, I'd go for a 12 gram tyre-inflator connected to a modified schraeder hammer valve with the lobed barrel, and set it up so that squeezing a single trigger opened the CO2 and started the motor spinning. A 9v battery would power a small motor, geared down, just fine especially as I wouldn't bother with the o-rings, so friction shouldn't be a big issue. I'd err on the side of higher power and lower ROF, although I reckon you could probably still get 20-30 rps no problem.

Wrap the whole lot up in a Striling like body (think Imperial Stormtrooper) and it'd make a fine SMG.
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Unread postAuthor: Flash » Sun Apr 27, 2008 9:38 pm

Yes, I'm still working on this, I'm just lagging a bit because of school and other projects.

Updates:
  • found out that my parents have a small air compressor, now I have a constant air source
  • I'm building pneumatic Nerf gun that will let me test how well the spinning breach seals
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