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pneumatic grenade?

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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pneumatic grenade?

Unread postAuthor: bobgengeskahn » Wed Mar 10, 2010 7:31 am

I know that this has been approached before, both here: http://www.spudfiles.com/forums/delay-b ... 16686.html

and here:
http://www.spudfiles.com/forums/air-del ... t6083.html

but I have been up late thinking about this tonight and read through both of these threads and came up with my own design. I would have just posted on the end of the most recent one, but I'm not sure if its too old or what not seeing as I am relatively new here.

The idea that I have come up with would actually be very simple... I think. I would like to basically build a very short coaxial cannon that you would thread the cartridge of baby powder or what have you into the end of the barrel. For charging it and arming it there would be two fittings on the bottom. One would be a schrader to fill it, the other would be a drain cock valve like this: http://www.homedepot.com/Tools-Hardware ... ogId=10053

this way you would be able to carry it with you, charged and simply be able to open the valve to activate it. The delay would be dependant on A. how much you opened the valve and B. the priming volume of the chamber.

The advantage that I see to this would be that you would not have to deal with pressurizing it in the field and once you were out of the field you would not have to deal with replacing a burst disk or carrying a supply of them. What do you guys think? Like I said, I just thought of this tonight, if I have time tomorrow I think that I am going to try to get down to the Home Depot or Ace and try to build one, it really should not be that expensive.[/code]
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Unread postAuthor: iknowmy3tables » Wed Mar 10, 2010 8:00 am

but if you have a slowly bleeding pilot your piston wouldn't open, you'd have to make a o-ring sealed piston with a check valve equalization hole
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Unread postAuthor: bobgengeskahn » Wed Mar 10, 2010 8:26 am

oooooooooh, true that. thanks for the attention to detail! :tongue1: my mistake :oops: but otherwise... it looks like it should work...
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Unread postAuthor: Hubb » Wed Mar 10, 2010 8:59 am

A bleeding pilot valve...I like it.

But the only real advantage I see is that it can be already charged before use. Grenades are one time use during an event (be it paintball or airsoft) so swapping burst disks between games is really no big deal.

It may be a little more complicated to build, but it might be worth it. We will just have to see.
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Unread postAuthor: bobgengeskahn » Wed Mar 10, 2010 9:52 am

yeah, for simplicity I'm now thinking that I'll just have the piston expose a bleed to a chamber with a burst disk in it. That way I wont have to deal with building an O-ring and a check valve onto the piston... we'll just have to see what I can come up with when I go to the toy store this afternoon :D

EDIT: Also, would anyone know the thread size for those butane valves you can pull off of lighters or those ones you pull off of Airsoft pistol mags? I have some laying around from some CO2 conversions I did a while ago, and I'm just thinking that in the field it would be easier to fill a grenade with green gas or propane to a constant pressure, rather than having a compressor with me and then having to check the pressure every time I fill them, that way the time delay will be a little more constant (i think???) with whatever burst disk material I use.
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Last edited by bobgengeskahn on Wed Mar 10, 2010 9:57 am, edited 1 time in total.

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Unread postAuthor: Hubb » Wed Mar 10, 2010 9:56 am

Check valves and seals aren't that complicated to put into a piston. The Sprinkler Valve does it in one of it's modifications and makes for a fairly lightweight, thin piston (which is probably ideal for what you are wanting to do). If you're interested, the e-book can be found in my library.
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Unread postAuthor: iknowmy3tables » Wed Mar 10, 2010 11:07 am

hey since you need this to seal pretty well why don't you try a diaphragm, this way you don't have to machine o-ring grooves, it will also help make the device lighter which will make it safer to drop and throw
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Attachments
grenadeforbob.PNG
grenadeforbob.PNG (4.74 KiB) Viewed 1664 times
grenadeforbob2.PNG
if you make the diaphragm seal really well with extra silicon and rubber based glues, then you can use a chamber sealing design for better dispersion
grenadeforbob2.PNG (6.91 KiB) Viewed 1664 times

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Unread postAuthor: bobgengeskahn » Wed Mar 10, 2010 11:12 am

WOW :shock: after I read some of Hubbs posts I was just contemplating how to do a diaphragm while I was on my morning run... and here you post this!! you guys are freaking geniuses I swear :D
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Unread postAuthor: Lentamentalisk » Wed Mar 10, 2010 12:46 pm

The problem with the 2nd design is t that it would be incredibly challenging to fill with powder, and keep from leaking powder, when at rest.

With the 1st one, you could make a little friction fit in cap, that slides into the "barrel" that is designed to disperse the powder evenly.

Also, with both of those, you will need a one way valve equalization hole in the diaphragm. Not impossible, but challenging.
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Unread postAuthor: Solar » Wed Mar 10, 2010 3:05 pm

My design uses the same style piston valve used on the Eclipse launcher which uses surface area differential to activate. No need for one way check valves with that style valve. Through experimentation it seems that the bleed hole needs to be somewhere in the 7-12 thousands size for a 6inch long, 40mm grenade with a 2 inch delay chamber. Of course a hand held can easily handle a larger air delay chamber so you won't need as precision a bleeder hole.

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Unread postAuthor: bobgengeskahn » Thu Mar 11, 2010 12:55 am

well, i gave it a shot today... it was ugly, but it was just a proof of concept... and it failed lol. I tried to base it off of the second diagram that iknowmy2tables posted... i took pictures so ill upload those once i can find my camera cable and let those do the talking...
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Unread postAuthor: iknowmy3tables » Thu Mar 11, 2010 4:50 am

yeah a chamber sealing piston is really tricky, the diaphragm has to be thicker and it has to seal perfectly around the edges while in a barrel sealing piston it doesn't, I'm looking forward to seeing this

btw while on the subject of pneumatic grenades I might as well mention one of my impact detonated designs, the design works as long as the nail is directed into the burst disk and has as little wiggle room as possible
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Unread postAuthor: i-will » Fri Mar 12, 2010 1:56 am

this is way more simple. read and understand it. http://www.airsplat.com/Itemdesc.asp?ic=AC-AI-GRENADE-T&eq=&Tp= I'm pretty sure Solar knows all about this. gas is trapped between two pistons of differing diameters. a leak at one end is the delay. the link explains it in great detail. the whole valve is only two or three parts.
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Unread postAuthor: iknowmy3tables » Fri Mar 12, 2010 12:23 pm

please tell me that you're joking, cause that's not more simple. do you even understand the design we're talking about? because I'm sick of the various people I've encountered this week claiming that something is more complicated just because they don't understand it

the design we're discussing is not much more than a piston valve, that design requires multiple o-ring seals of different diameters which is not easy to make unless you've got a machine shop
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Unread postAuthor: bobgengeskahn » Fri Mar 12, 2010 3:20 pm

GAR!!!! :twisted: I was just about to upload the photos... and apparently the cable to upload and the cable to charge are NOT the same... and the battery just died... so im on the hunt again... hopefully ill have them up by tonight for those interested
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