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Unread postAuthor: jeepkahn » Sat Apr 04, 2009 9:00 am

here's a thought, take an off the shelf qev, attach a short nipple and endcap(to house the spring) and screw it into the pilot orifice, fill at the chamber and voila, you just saved yourself years of fiddling and a ton of epoxy... :D :shock: :twisted:

you may want to put a thin metal disc where the springs meets the shuttle/piston to reduce wear....
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 04, 2009 9:19 am

jeepkahn wrote:here's a thought, take an off the shelf qev, attach a short nipple and endcap(to house the spring) and screw it into the pilot orifice, fill at the chamber and voila, you just saved yourself years of fiddling and a ton of epoxy... :D :shock: :twisted:


isn't this what POLAND_SPUD had suggestedhere?

On another note, I'm questioning the wisdom of using lead pellets. I went through quite a bit of lead this morning, not cheap even for shitty brands and definitely not reusable. Maybe BBs would be a better idea to keep running costs down.
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Unread postAuthor: jeepkahn » Sat Apr 04, 2009 9:28 am

Yes, they did suggest it in a form, but the discussion turned into flipping pistons, reversing qev, etc etc...

I'm suggesting barrel goes in normal spot, chamber goes in normal spot, the only mod would be it'd be a spring pilot instead of air pilot....
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Unread postAuthor: Gippeto » Sat Apr 04, 2009 9:30 am

Jack, have you tried limiting the travel of the piston?

I'm curious as to whether the reduction in dead space and energy consumed to compress the spring would increase velocity.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 04, 2009 9:41 am

Gippeto wrote:Jack, have you tried limiting the travel of the piston?


Very interesting point you make there :) and dammit I just finished clearing out all the debris from the garage!

edit: I limited piston travel to 3mm, which for a 10mm port is more than enough flow considering it exhausts through a 5mm tube. Pellets were travelling some 50 fps slower than an unrestricted piston, I'm guessing the energy lost compressing the spring is compensated for by the increased piston momentum and therefore dwell time.

This morning's lead consumption:
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Unread postAuthor: SPG » Sat Apr 04, 2009 11:37 am

Go on then, work out how to put it through GGDT so you can optimise the thing.

Methinks you might be better with BB's lead costs a lot, unless of course you melt it down and find another use for it.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 04, 2009 12:00 pm

SPG wrote:Go on then, work out how to put it through GGDT so you can optimise the thing.


How's this for optimisation, having the BBs within the pressurised chamber and a single BB comes out with every pop. Trying to figure out how that would be done though.
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Unread postAuthor: SPG » Sat Apr 04, 2009 12:05 pm

NOOOOOO Don't do it, just get this working well.
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Unread postAuthor: psycix » Sat Apr 04, 2009 2:50 pm

jackssmirkingrevenge wrote:I have to say I prefer this to QEV+popoff, for two main reasons. First of all, there's no wasted air - it's all going out of the barrel, unlike a pilot valve. Secondly, you know that when it fires, the chamber is up to maximum pressure. I have a feeling that the QEV fires before the chamber has had time to fill completely.

Clearly MOAR SPRING = MOAR POWER! :D

True, I am going to fix that in my next design. And I already know how, I may throw it out someday if you like.

Well, since my marble gun has gage on the chamber, I think that it will not matter more then half a bar. This depends on how restrictive of flow the piston is.


Well, ofcourse, we all expected that right?


jackssmirkingrevenge wrote:How's this for optimisation, having the BBs within the pressurised chamber and a single BB comes out with every pop. Trying to figure out how that would be done though.

Have the piston travel through a pipe with a hole drilled in it. The only way to the barrel is the hole, which is just above barrel caliber.
This will allow no more then one bb to enter when the piston clears from the hole.
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Unread postAuthor: VH_man » Sat Apr 04, 2009 6:01 pm

why not make the "pop" piece actuate the bolt?

seems like it would be easy enough.
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Unread postAuthor: jackssmirkingrevenge » Sat Apr 04, 2009 7:50 pm

psycix wrote:True, I am going to fix that in my next design. And I already know how, I may throw it out someday if you like.


Feel free to share ;)

Have the piston travel through a pipe with a hole drilled in it. The only way to the barrel is the hole, which is just above barrel caliber.
This will allow no more then one bb to enter when the piston clears from the hole.


One thing I realised for these valves to work reliably is that the outlet to the barrel should be exposed immediately after the piston begins to move, otherwise it will tend to hang open.

That's why this design as it is wouldn't work.

why not make the "pop" piece actuate the bolt?


Something like this?
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Unread postAuthor: VH_man » Sat Apr 04, 2009 8:31 pm

jackssmirkingrevenge wrote:Something like this?


Precisely hahaha. I feel like your attempting this as we speak.
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Unread postAuthor: clide » Sat Apr 04, 2009 10:57 pm

Congrats on finally reaching your goal. Now you just need to scale it up enough to be able to do that to a real digger :twisted:
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Unread postAuthor: POLAND_SPUD » Sun Apr 05, 2009 1:00 am

I know I mentioned it earlier but IMO this has to be stressed... chooseing the right caliber is one of the most important thing with semis and most likely with full autos

I asked whether you want to use marbles but they might be a little bit too big for a full auto... not to mention that they sometimes do not fit in the barrel

the other problem is likely to spring due to relatively high muzzle energy of such launcher... you can't do tests with them indoors and you have to make sure that there are no riquochetes... normally I just put the target at least 10 meters away for safety reasons but becasue of that I lose some marbles...

so in other words... they aren't ideal and they make testing difficult... sure they are cool becasue of greater power but unless you have a lot of space and a good compressor 6 mm BBs are better
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Unread postAuthor: jackssmirkingrevenge » Sun Apr 05, 2009 1:46 am

VH_man wrote:Precisely hahaha. I feel like your attempting this as we speak.


Not just yet. In that design, by definition the bolt is not closed when air starts getting into the barrel, I need a better solution.

clide wrote:Congrats on finally reaching your goal. Now you just need to scale it up enough to be able to do that to a real digger


Thanks :) if only I had the resources!

so in other words... they aren't ideal and they make testing difficult... sure they are cool becasue of greater power but unless you have a lot of space and a good compressor 6 mm BBs are better


Fair point regarding marbles, I definitely wouldn't have the space to test an auto marble gun at home. I think I'll stick with 4.5mm BBs, hard spherical projectiles are definitely the easiest to make a loading mechanism for, as well as the most economical as the are likely to be re-used. It would be better if I had an easy and cheap source for 6mm steel bearings but they are not readily available.

VH_man wrote:Precisely hahaha. I feel like your attempting this as we speak.


Not just yet. In that design, by definition the bolt is not closed when air starts getting into the barrel, I need a better solution.

Hmmm...
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