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Gas piston surface area question (for an [semi-]automatic)

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Gas piston surface area question (for an [semi-]automatic)

Unread postAuthor: Tsukiten » Sun Apr 11, 2010 3:46 am


Hey guys!
I've designed many automatics prior to this one, but they were all too complicated and hard to build from standard materials. So I decided to go open-bolt style and have the bolt as one solid chunk of aluminium piping. The result is quite elegant, I must say :wink:
But there's an issue. You can read about it in the image.


Image
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Unread postAuthor: Crna Legija » Sun Apr 11, 2010 4:07 am

lol that one look complicated to :lol:
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Unread postAuthor: Tsukiten » Sun Apr 11, 2010 1:33 pm

My apologies but, bumpin' for an answer.
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Unread postAuthor: DR » Sun Apr 11, 2010 2:07 pm

3.86lbs. to 5.78lbs. of force? I am SO friggin' braindead today., that I wish I didn't even reply now....

Metric to standard conversion aggravates me more than anything else.
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Unread postAuthor: iknowmy3tables » Sun Apr 11, 2010 10:11 pm

hey no bumping, a day hasn't even passed by yet,

hey DR wana see a trick for conversion, you might know it, go on google and type "6 bar to psi" it works for most conversions

I like your design is it based on anton's auto ? the part about having a popet hammer valve and piston dedicated to cycling, it's a more streamlined design I like it, oooh and the air comes from tanks in the mags, this designs in great your awesome, now only if you can pull it off

I'm afraid we can't mathematically find you an answer, there's too many variables, the seal around the piston isn't perfect, the friction varies, we don't know how much air is going to come out of the valve and how fast. so I'm going to have to bs the most of my advice without first hand experience,

NGGAAAHHH I am IKM3T BS GUESSTIMATING EVALUATOR 9001
engage bs geustimations
looking at working examples...
comparing surface area's of pistons...
surfaces areas seam sufficient for operation, design has benifet of additional surface area in the piston near the primary firing valve
comparing valves...
!!!
anton's auto has valves along the same axis of movement as pistons, you design translates movement of pistons by angled sliding planes
!!!!
SLIDING PLANES NGAAAH.. danger danger tsukitten the sliding planes contain large amounts of friction that will very likely make this design not operational
!! danger danger as valve is pushed forward it is pushed into the wall of the it is housed in generating even more friction....
generating diagram...
Image
diagram contains areas of particularly high friction in red, anton's prototype contains virtually no friction in the traversing of movement towards opening the popet,
to fix this please redesign the poppet to open when "tilted" or "toggled" rather than restricted linear movement...
proceeding with comparison...
moving bolt/hammer is smaller and streamlined, probably lighter, may benefit from additional mass,
proceeding with comparison... ammo loading part of bolt is opened very far in locked position, extend it so it's just enough for the ammo to feed in the locked open position, this way the bolt ammo bolt is closed for the majority of the stroke so it's less likely to open prematurely
comparison complete
IKM3T BS GUESSTIMATING EVALUATOR 9001 is shutting down
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Unread postAuthor: Tsukiten » Mon Apr 12, 2010 12:31 pm

iknowmy3tables wrote: --post was somewhat too long to include in here--


What an odd reply :D though creative
And informative; about the hammervalve friction problem, I think I'll just try some lubrication first. If it doesn't work after that, I could just pop in a new valvehead.
The large distance the bolt has to travel is an attempt to slow the rate of fire, as I expect it to go absolutely berserk if it only has to move half an inch to cycle. Alternatively, I could use a roller-delayed action used in the HK G3 rifle.
see: http://img504.imageshack.us/i/rollerdelayedblowback.jpg/

But thanks for the extensive reply :wink: I guess I'll just build the darn thing

The finished diagram to watermouth over:
Image
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Unread postAuthor: iknowmy3tables » Mon Apr 12, 2010 2:10 pm

writing replies late at night, actually it wasn't that late, I guess I am that strange, maybe I am a dragon

so the the length of the bolt stroke was not my concern, a long bolt stroke is good if it works. there's a diagram below of what I'm suggesting,

no need for any delay mechanism you can just adjust the cycling piston

now those valve, I don't think lube is going to cut it, like I said anton's auto has virtually no friction in translating the piston stroke to opening the poppet,

I don't think your valve setup is going to be enough, think about it your pistons are expected to do enough work in under 2mm of displacement, to open a poppet valve that opens less than 2mm which will provide enough air to fire the bb and cycle everything?
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 12, 2010 2:25 pm

Beautiful rendering but I can think of much simpler and efficient designs for hammer valves in practice, here's some not-so-original ideasI had floated around ;)
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Unread postAuthor: Tsukiten » Mon Apr 12, 2010 2:51 pm

jackssmirkingrevenge wrote:Beautiful rendering but I can think of much simpler and efficient designs for hammer valves in practice, here's some not-so-original ideasI had floated around ;)

Thank you for your idea and opinion, however. I want to create a balance between simplicity and functionality.
Two things I really wanted were (1) an o-ring sealing for the barrel & bb so it does not roll out and is more efficient, and (2) not to have the gastank below my cheek, which I honestly find terrifying.
While the former is not archievable in a moving barrel design, in the latter case I decided I could just build the airtank into the magazine (other ideas had the tank wrapped around the barrel) .
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Unread postAuthor: Tsukiten » Mon Apr 12, 2010 3:06 pm

iknowmy3tables wrote:I don't think your valve setup is going to be enough, think about it your pistons are expected to do enough work in under 2mm of displacement, to open a poppet valve that opens less than 2mm which will provide enough air to fire the bb and cycle everything?

I don't get the part where the piston only gets 2mm of displacement (more like 2 cm), but then I probably am mistaking what you mean...

But if I would use larger, bulkier parts, and change the checkvalve design, then it might work, right?

iknowmy3tables wrote:maybe I am a dragon

Could be. Last time I checked, I was a Range Rover.
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Unread postAuthor: iknowmy3tables » Mon Apr 12, 2010 10:01 pm

@jsr: but in practice blow forward hammer valves are not easy as we have both tried with little success. the success of Antonio's design lies in the dedicated valve for cycling that provides air power for cycling that isn't rapidly drained out the barrel,

@tsukitten
sure there's about 2cms of displacement in the over all piston stroke length, but the amount of distance that the piston moves while in contact with the and valve in less than 2mm and with those 2mm the piston must exert enough work on the valve to open it enough to cycle the whole thing and the valve doesn't even open more than 2mm
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 12, 2010 11:22 pm

iknowmy3tables wrote:but in practice blow forward hammer valves are not easy as we have both tried with little success.


Fair comment, my minature fart machine comes to mind :roll:

I would consider moving away from a pure hammer valve for semi auto and going with a hammer piloted QEV. You could still make a neat setup with the chamber in the magazine, this is what I had drawn up:

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Unread postAuthor: Gaderelguitarist » Mon Apr 12, 2010 11:58 pm

I guess I'll just build the darn thing

The finished diagram to watermouth over:


If you build it, they will drool.

By the looks of your rendering, I'd say you've devised a method of having the magazine/air chamber setup removable. If so, this opens the possibility of carrying multiple fully charged, fully loaded chamber mags.

Couple that with a more simple valve and you'll have a lot of people scrambling for the hardware store with hopes of duplication.
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Unread postAuthor: iknowmy3tables » Tue Apr 13, 2010 10:03 pm

Tsukiten wrote:But if I would use larger, bulkier parts, and change the checkvalve design, then it might work, right?

I overlooked it before but you mentioned the check valve design? by this do you mean the poppet, because I was suggesting that you change the poppet to open when tilted/toggled
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