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Rattlesnake V3 - HPA auto valve

Built a BB Machine Gun? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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Unread postAuthor: jook13 » Wed Apr 29, 2009 12:04 am

My only regret is since few like working with epoxy like I do


Dont worry Jack, I got yo' back dawg. I am all about the epoxy goodness.

If I were ever to work with an auto bb gun, I would try like hell to make it work with .177 bb's because they are easy to find, consistant in size, and cause lots of damage. Also, I dont care too much about airsoft for my purposes.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 29, 2009 12:18 am

jook13 wrote:Dont worry Jack, I got yo' back dawg. I am all about the epoxy goodness.


Good to hear that the gospel has spread to some extent, however given certain disadvantages I can understand how it hasn't caught on that much. Still, used in conjunction with standard parts, the design possibilities multiply without significant increases in cost.

If I were ever to work with an auto bb gun, I would try like hell to make it work with .177 bb's because they are easy to find, consistant in size, and cause lots of damage. Also, I dont care too much about airsoft for my purposes.


0.177" BBs make sense in terms of availability and cost but when it comes to performance, at the back of my head there's the constant maxim that you can always make a bigger hole :D
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Unread postAuthor: SPG » Wed Apr 29, 2009 4:11 am

Nope stick with .177 you know you want to, and then move from there to .177 pellets once you've got a feed system working. Sure you can make a bigger hole but I reckon the next thing is to make a more accurate hole, and from further away.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 29, 2009 5:14 am

SPG wrote:Nope stick with .177 you know you want to, and then move from there to .177 pellets once you've got a feed system working. Sure you can make a bigger hole but I reckon the next thing is to make a more accurate hole, and from further away.


If it was a single shot launcher I would be thinking along the same lines, but when it comes to full auto I'm not looking to make a tack-driver, I would be happy with a 12 inch group at 45 yards.

Thing is, say you had to strike a hypothetical fluid filled container with a 0.177" pellet, it would flow out at a rate of x mL/min. Make it a 0.22" pellet, and now you've got a flow rate of almost 1.5x mL/min.

It's the (hypothetical, as always ;) ) "big hole" schoolof thought.
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Unread postAuthor: SPG » Wed Apr 29, 2009 5:50 am

jackssmirkingrevenge wrote:If it was a single shot launcher I would be thinking along the same lines, but when it comes to full auto I'm not looking to make a tack-driver, I would be happy with a 12 inch group at 45 yards.

Thing is, say you had to strike a hypothetical fluid filled container with a 0.177" pellet, it would flow out at a rate of x mL/min. Make it a 0.22" pellet, and now you've got a flow rate of almost 1.5x mL/min.


You've still got to hit the hypothetical container though, and a foot grouping at 45 yards is going to be a lot of hypotheticals.

And of course there's the decision about penetration too, I've got a couple of cheap air-pistols on in 0.177 and one in 0.22, the 0.177 will penetrate both sides of my hypothetical container, the 0.22 just the one.

So while flow rate of the entry hole is 1.5x mL/min, if you count both holes then the 0.177 gives me 2x mL/min minimum especially as the exit hole is often bigger.
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Unread postAuthor: Solar » Wed Apr 29, 2009 6:36 am

Those Ninja paintball tanks and regs are fantastic. I can run two on an Eclipse to keep it light and sleek as opposed to peanut tanks which aren't as ergonomic. Once you get it perfected perhaps I could build up a larger machined version for "experimenting" with. So what if it is an air hog, I am thinking hooked to a compressor on a vehicle it would be utter devastation using a well stocked 40mm rubber bullet magazine.
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Unread postAuthor: jackssmirkingrevenge » Wed Apr 29, 2009 8:37 am

SPG wrote:You've still got to hit the hypothetical container though, and a foot grouping at 45 yards is going to be a lot of hypotheticals.


It's not great performance for single shot launcher but if you can put 30 rounds in a 12 inch circle in a matter of seconds, that's a pretty good hit probability, involving multiple rounds.

So while flow rate of the entry hole is 1.5x mL/min, if you count both holes then the 0.177 gives me 2x mL/min minimum especially as the exit hole is often bigger.


Good point, but if you can get the 0.22" to penetrate both sides of the container, that's 3x flow and that's the sort of performance I'm going for ;)

Solar wrote:Once you get it perfected perhaps I could build up a larger machined version for "experimenting" with. So what if it is an air hog, I am thinking hooked to a compressor on a vehicle it would be utter devastation using a well stocked 40mm rubber bullet magazine.


The concept is perfected, here are the criteria I had established for it to work well:

earlier post wrote:It is important the that piston doesn't obstruct the outlet when it's closed, otherwise when returning from the first cycle it will encounter pressure and "hang" - In my design (the second one is essentially the same aside from the substitution of the air spring with a coil spring) I avoided this.

In terms of dimensions I had already mentioned two critical factors earlier in the thread:

1) The piston seat must be significantly bigger than the outlet to the barrel, to ensure that the piston chamber fills with pressure faster than it can empty and the piston has time to actually pop

2) The piston must be significantly wider than the piston seat, in order for there to be enough area for the pressure to act on and overcome the spring strength.

The other two relevant factors are spring strength and rate of flow into the chamber. The spring setup I'm currently using will pop at around 80 psi, and my compressor starts out at 110 psi. Flow into the chamber is also important to establish reliable functioning and rate of fire. I adjust this using the flow control knob on my compressor, in this case it is a question of finding the "sweet spot" for a given pressure and spring strength.


You could easily scale the design up for a 40mm launcher, with your machining facilities and skills it should be a doddle ;) and as cool as the Eclipse is, I think a vehicle mounted variation firing on full auto would make a hell of an impression :D

Those Ninja paintball tanks and regs are fantastic.


Couldn't agree more, methinks I'm going to buy another one :)

update: I made a 0.177" barrel and magazine setup, the layout is very similar to the one SubsonicSpud proposed here. The magazine barrel juntion and detent have all been set in a cast epoxy block, testing due when it's cured :)
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 02, 2009 12:43 am

I was looking through google patents, as one does, and it looks like there's nothing new under the sun, here's a patent for a pop-off valved pneumatic auto that dates back to 1927!

It sure pays to do your research before reinventing the wheel :roll:
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Unread postAuthor: Ragnarok » Tue Jun 02, 2009 10:44 am

I'd point out that patents don't always work, nor are they the best way to do something. It just means the idea is unique, not that it will do what it says it will.

For an example, there are a number of patents for perpetual motion machines.
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Unread postAuthor: psycix » Tue Jun 02, 2009 11:20 am

Cool. We are not the only generation with this hobby.
It has a simple T loader though...
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Unread postAuthor: jackssmirkingrevenge » Tue Jun 02, 2009 11:27 am

Ragnarok wrote:I'd point out that patents don't always work, nor are they the best way to do something. It just means the idea is unique, not that it will do what it says it will.


True, but chances are that if you've had an amazing idea, someone's probably thought of it already, so it is worth doing research.

psycix wrote:It has a simple T loader though...


... but also featuring an electrically driven paddle to agitate the ammunition too, something very similar to one concept I had proposed a long time ago on spudtech when I was experimenting with the "ball valve strafer" idea:
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Unread postAuthor: Technician1002 » Tue Jun 02, 2009 12:09 pm

jackssmirkingrevenge wrote:
So while flow rate of the entry hole is 1.5x mL/min, if you count both holes then the 0.177 gives me 2x mL/min minimum especially as the exit hole is often bigger.


Good point, but if you can get the 0.22" to penetrate both sides of the container, that's 3x flow and that's the sort of performance I'm going for ;)


Me too. See photo

1) The piston seat must be significantly bigger than the outlet to the barrel, to ensure that the piston chamber fills with pressure faster than it can empty and the piston has time to actually pop

2) The piston must be significantly wider than the piston seat, in order for there to be enough area for the pressure to act on and overcome the spring strength.


I don't find that is always true. On 1, if the piston is not much heavier than the projectile, the pressure building between the projectile and piston face takes care of the needed pressure. It works well for me. I get pistons to pop where the piston is the same diameter as the barrel.

On 2 this is true if the spring is too big. If the spring is small enough so the valve will open with the small opening force provided, it pops open better if the seat is larger because the force to open it rises faster with a larger seat.
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Unread postAuthor: jackssmirkingrevenge » Wed Jun 03, 2009 12:23 am

Technician1002 wrote:High speed impact makes large holes.


Having fluid in the target also helps, as it helps to transmit the shockwave beyond the actual path of the projectile. It doesn't have to be very high speed either, with this launcher for example, shooting a water filled coffee can with a marble doing less than 500 feet per second was still enough to blow the lid off through hydrostatic shock.

I don't find that is always true. On 1, if the piston is not much heavier than the projectile, the pressure building between the projectile and piston face takes care of the needed pressure. It works well for me. I get pistons to pop where the piston is the same diameter as the barrel.


Granted, with a projectile in the barrel the outlet is effectively blocked off allowing for pressure buildup so this parameter is not essential, but I was outlining specifications that would guarnatee pop-off function independently of barrel attachment and projectile feed.

On 2 this is true if the spring is too big. If the spring is small enough so the valve will open with the small opening force provided, it pops open better if the seat is larger because the force to open it rises faster with a larger seat.


The disparity between seat and piston size makes a difference though. Say you have a 0.5" seat with a surface area of 0.196 in<sup>2</sup>. This means that a spring with around 20 lbs of force will pop at 100 psi.

Say you had a 0.55" piston, at 100 psi there will then be - ignoring pressure losses by expansion - 24 lbs pushing the piston, this is greater than the spring strength so it should pop open. However with the same setup and say a 0.75" piston, not much bigger, there's now 44 lbs pushing on the spring.
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Unread postAuthor: kenbo0422 » Sat Oct 31, 2009 1:34 pm

Would this kind of design be helpful to keep your BB's from doubling up? The spring loaded magazine will push one BB or pellet into the elevator. You can use a magnet to hold the BB in place. No detents or O-rings to hinder your flow. The incoming feed from your valve will be stopped by the valve effect at the top of the elevator. The pressure will push the elevator up and release the BB. Once the pressure has subsided, the spring returns the elevator to capture another round.

This was originally a mechanically activated device in an old CO2 rifle.
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Unread postAuthor: psycix » Sat Oct 31, 2009 1:37 pm

Ah, a "falling block". Complex, but could work...
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