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Old 04-14-2011, 07:50 AM #43
jonotwist
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Quote:
Originally Posted by Spitlebug View Post
That doesn't make it metered. Metered would be the air source blocked during firing cycle.
you know what i forgot that until the full forward stroke is complete it will dump now that i picture it in my head. was working on a clone on my desk while i was typing that. for some reason i had a clone hybrid that i was thinking of, and one my buddy dropped off his UL slg, i noticed that.
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Old 04-14-2011, 10:37 AM #44
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Originally Posted by jonotwist View Post
you know what i forgot that until the full forward stroke is complete it will dump now that i picture it in my head. was working on a clone on my desk while i was typing that. for some reason i had a clone hybrid that i was thinking of, and one my buddy dropped off his UL slg, i noticed that.
The SLG bolt will come back because it has a pressure differential air spring, and it does shutter back and forth when the sear doesn't catch, but that is not a function of closing off the dump chamber during the firing cycle.
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Old 05-01-2011, 06:58 PM #45
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the bolt doest have any springs.

I see where i was off on thinking. once the bolt reaches full forward stroke is where air ceases to flow down the barrel. not metered.
i still claim partial credit lol.
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Old 05-02-2011, 03:32 AM #46
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Originally Posted by jonotwist View Post
the bolt doest have any springs.

I see where i was off on thinking. once the bolt reaches full forward stroke is where air ceases to flow down the barrel. not metered.
i still claim partial credit lol.
Air spring. It means air that is passed into the bolt from the small hole in the front acts as a spring to push the bolt back.
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Old 05-03-2011, 01:41 AM #47
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Hey guys,

Nice bolt parts you have there Bob. The machining looks great! Did you single point those threads or are these modified parts? It's a shame your shelving the project- why?

I can see how people would get confused as to if the SLG dump chamber is metered. The dump chamber itself cannot fill when the main valve is open. But then there is flow through that small hole and it does introduce additional air into the barrel.

The purpose of that small hole in the SLG bolt is two fold. One, when the bolt is rearward, it restricts flow filling the chamber so that the bolt pauses rearwards and gives the sear a chance to catch. Two, it alleviates a compression problem we were having- pressure would build up too fast in the 'air spring'.

On the topic of airpath. The flow is most definitely turbulent choked flow. Upstream pressure and valve area should determine flow. Significant change in direction- 90* or 180* aren't as efficient, but I don't think the airpath is as significant as you might think. Volume between ball and valve is another story as is minimum cross sectional area of the valve. I'm curious what you guys think about that.
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Old 05-03-2011, 04:57 PM #48
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I think they're all contributing factors, and when you hit a certain point the beneficial aspects of paying attention to the "lesser important" aspects of the airflow grow drastically in their importance. Of the actual fluid dynamic aspects of a system (i.e. ignoring valve resolution), I agree that volume between valve seal and ball is one of the most important aspects of efficiency, but I would probably place almost as much emphasis on smooth airflow.
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Old 05-03-2011, 05:21 PM #49
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Thorp,

"dede!" like the magic trick?
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Old 05-03-2011, 08:36 PM #50
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I think It's Dede like from Dexters Laboratory.

Anyways, I prefer small and smooth transitions from pressurized air to ball. Though sometimes it is harder to machine. (but sometimes it is easier!)
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Old 05-04-2011, 12:56 AM #51
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or maybe it's more like deeeeeed!

In regards to that volume between valve and ball- I believe it hurts efficiency but also helps reduce ball breakage by reducing peak accelerations.

I've built an iterative simulation in matlab of a marker firing. I will change that volume and see what that does to velocity and peak accelerations. (I've done this before, but it's been too long!)

Empirical testing is often times better but can also be a bunch trickier. A way to test this could be to start the ball down the barrel two inches, with a two inch longer barrel, and compare.... efficiency is easy to test with velocity but peak accelerations ... either a transducer placed at the mouth of the barrel or lots of testing with delicate paint.

But enough of this BS... why isn't the Icarus firing?!
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Old 05-04-2011, 02:28 PM #52
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I remember an article a while back (like, pre 2000, and I completely forgot the author) about pressure behind the ball in the breech - under 50psi it used way too much air, over 100psi it caused the ball to break on a consistant basis.

The idea was that you needed to adjust the air pressure in the breech to make sure it wasn't to high or low. This was at the time of 800psi guns, with the shocker, nova and AKA being wildcards at sub 200psi operation.

Then as I was doing massproperty calculations trying to figure out the volume of air I needed for the Shiva I ended up trying to figure the total volume calcuations for a gun. And it was very consistant. If the ball was about 8" down the barrel (might have been 6-12", I forget at the moment, that was a decade and 3 children ago) all of the guns, dependant of their operation pressure and the total volume of the dump chamber/valve chamber, would have a about 50psi of pressure in the system. So, take a gun, plug it at the reg or right before the dump/valve chamber, put a blocker in down the barrel at the same length, and discharge it, and you would hold (if the bolt didn't leak, etc) 50psi average at one cycle.

Just a weird bit I found out a while back. It worked on a Phantom, a cocker, a Shocker (old school, this was a while ago) a Mag, a Tippmann, etc.

I built the Shiva with a very simple air path, a bit different then the Closed Bolt Ion (they are near enough to the same gun design) longer and more consistant with a smaller discharge hole, to reduce initial air pressure (I ran a little under 1" chamber at 165psi.)

I also ended up with very excellent efficiency, nearing 165in*lbs of energy per shot. AKA Vikings ran about that, with the Shoebox Shocker running 365in*lbs (most guns average 225-250in*lbs per shot.)

In later part designs I kept the same airpath, in one case making an Ion/Epiphany bolt that runs in the 150in*lbs per shot range. Now that GOG is making the ion line again, I might put that one into production.

I have to say the simple, small, clean airpaths have worked to consistantly produce guns that are very efficient, but I also looked at figuring out the volume of the chamber and operating pressure based on total volume of the gun with the ball in the chamber.

I think it was 6" down the barrel...

Josh
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Old 05-04-2011, 05:41 PM #53
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Any chance it was written by Tom Kaye? He did A LOT of technical research for our little game.
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Old 05-04-2011, 06:08 PM #54
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No, I would have remembered if it was Tom Kaye - we did a good chunk of back and forth concerning gun action and a few other things back during Automags Online's heyday.

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Old 05-04-2011, 08:56 PM #55
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Here are the plots I said I'd post. They illustrate what you'd expect, increasing volume between valve and ball, peak accelerations decrease as does velocity.

Still, it's nice to quantify some of this stuff- how much velocity do you lose for a given increase in volume. It's a great tool to use for a sensitivity analysis- how much do each of these parameters effect the end result, ball flying out of the barrel.

It's nice to see your still around Josh I remember reading posts about your Shiva back when I was in..... middle school? I remember seeing a cad screen shot and thinking "whoooaooaoa!!!!! sooooo cooool!"





With the screen shots, it helps to save them to your computer and then cycle through them with a viewer instead of going in and out of imageshack.
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Old 05-05-2011, 12:40 PM #56
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That is interesting. The pressure, What is it measured in? It doesn't seem to be psi is it? Or is that the number times 10 for actual psi?
Acceleration doesn't seem to be as affected as I thought it would be.

And isn't half a cubic inch massive dead space in most PB guns? I doubt there are any at 1CI either, but I haven't checked any.

(I checked one of my designs, 0.015CI dead space. Pretty difficult to machine though. And I think this is probably the least amount of dead space you could get.)
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Old 05-06-2011, 01:51 AM #57
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Since this seems to be a good place to ask...

Would a valve opening almost literally at the ball, say a bolt stroke away, be better for or detrimental to efficiency due to flow patterns? I was just thinking about possible improvements to the ion bolt system, and moving the "valve" closer to the ball. Hmm, if I ever get bored one day I just might do that! Having an XE helps lol
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Old 05-06-2011, 02:25 AM #58
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Yeah, I single pointed them. I actually eye-balled them, and the threads on the body gaulled.

I've been working on this project for to long, none of my friends paintball anymore. I was spending 16 hours a day making torpedos and paintball guns. I don't paintball, and I sure as **** don't fire torpedos.
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Old 05-06-2011, 04:47 PM #59
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Since this seems to be a good place to ask...

Would a valve opening almost literally at the ball, say a bolt stroke away, be better for or detrimental to efficiency due to flow patterns? I was just thinking about possible improvements to the ion bolt system, and moving the "valve" closer to the ball. Hmm, if I ever get bored one day I just might do that! Having an XE helps lol
I believe better. It is a very effective means of drastically reducing pre-expansion. Look at how close to the ball the valve seal is in my closed bolt Ion. One of my entires in the PBN FASOR design contest we had 2 years ago had the valve even closer.

http://www.youtube.com/lustenaderj#p/u/4/0EZ04Yt76sE
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Old 05-06-2011, 09:35 PM #60
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The valve can be right at the ball, if the air pressure is low. I have had too high of a pressure right at the ball and got nothing but breaks.

But look at the pgp: straight out of a 12 gram to right between the ball and bolt. Just through a tiny hole. So how the air is supplied, the pressure, and the size of the port are all factors.

With all of that, how does that explain the AKA cockers? Low pressure, long valve path, big turns, a .25"hole in the body.

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Old 05-07-2011, 02:30 AM #61
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thanks
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