Rattlesnake V3 - HPA auto valve

[Moonbogg]

Thats sweeeeet! Rattlesnake, perfect name for obvious reasons. It was cool to see it shooting also. I'm curious to see how this will continue to develop.

[mega_swordman]

I am just going by ear here, but it sounds like it drastically looses power as the tank pressure decreases (as it very well should). Any theories yet on how to combat this?

Also, looking at the first picture, is this actually valve #5? Those valves in the picture look nothing like the ones in the other threads.

[jackssmirkingrevenge]

Thats sweeeeet! Rattlesnake, perfect name for obvious reasons.

I was going with "Jack's hammer" at first but Brian suggested the current name and it made sense

I am just going by ear here, but it sounds like it drastically loses power as the tank pressure decreases (as it very well should). Any theories yet on how to combat this

Technically, it doesn't really lose power. Yes, the rate of fire decreases, but this is an indication that the actual muzzle energy should be the same, because the piston always pops at the same pressure. When that pressure is no longer available, it simply stops working.

Again I must stress that this was the tank operating at 66% of its full capacity and the valve is a "massive" full 6mm porting, if I cut that down to 3mm that's 4 times less flow so shot count should improve dramatically. I'll start construction after work, keep watching this space

Also, looking at the first picture, is this actually valve #5? Those valves in the picture look nothing like the ones in the other threads

The are the same valves, just with reinforcement around the piston (which should be noted if you look through the thread).

Actually the full development timeline for this particular design should be this:

Original pop-off piloted piston attempt

auto piston v2.0

auto piston v3.0

Modified pop-off valve

custom pop-off v1.0

custom pop-off v2.0

...leading me to the current valve, and already looking to make another

[ALIHISGREAT]

Actually the full development timeline for this particular design should be this:

Original pop-off piloted piston attempt

auto piston v2.0

auto piston v3.0

Modified pop-off valve

custom pop-off v1.0

custom pop-off v2.0

...leading me to the current valve, and already looking to make another

arn't you bored of the whole pop-off full auto thing yet

i would have given up after the first!

[psycix]

The list of fail...

[inonickname]

The list of fail...

It has been noted that there should be a graveyard just for JSR's designs. However, he cuts out their organs and re-uses them.

[psycix]

Instead of a graveyard, he drops the fails off onto the failboat.


But I believe its about to leave, making room for the succesboat, sometimes also called winboat.

[jackssmirkingrevenge]

The list of fail...

It's called Research and Development boerenlul

There has to be an amount of fail before one achieves win, that's the way these things work. You should consider yourself lucky that I post all my failures in such a manner that others can learn from my mistakes

Aren't you bored of the whole pop-off full auto thing yet

I would have given up after the first!

If I can end up with a portable submachinegun-type launcher firing 4.5mm BBs at high subsonic velocity at a rate of fire of 120-240 rounds per minute and a magazine + air capacity of at least 100 rounds, it would have been all worth it

[dewey-1]

The list of fail...

After 39 failed attempts, and the sucessful 40th; WD 40 was invented.

Just think, JSR has about 36 to go.

JSR is real close to sucess, like maybe version 4.0.

If so, it could be called; AP 40. [Auto Piston v4.0.]

You can do it .

[SPG]

Ok mister look-I-finally-got-it-working, there's a couple of things we need aren't there?

First, chrony the damn thing, shooting stuff is fine but I want figures.

and

Second, any idea what pressure you're popping at? It'd be interesting to have a pressure gauge mounted in your chamber so you could see no just the pop-off pressure but also the pressure drop as well.

Which leads me on to a couple of thoughts about test set-ups.

You mention your porting's too big, why not drill and tap down into your current porting, screw in a bolt witha rounded off end, and then adjust this in and out to get the best rate of flow (or of course make yet another new one, and fit a ball valve in between chamber and valve)?

It'd also be interesting to see whether differences in expansion chamber volume change the behaviour, but off the top of my head I can't think how to make a variable volume expansion chamber.

[jackssmirkingrevenge]

Just think, JSR has about 36 to go.

Oh come on, I'm *this close* to getting the final prototype I've always dreamed of

First, chrony the damn thing, shooting stuff is fine but I want figures

I wanted to chrony it but someone, in his endless overenthusiasm, abused the device before the epoxy had full cured and now the valve-tank fitting has come loose, so it needs to be repaired. In the meantime I'll start the smaller version.

Any idea what pressure you're popping at? It'd be interesting to have a pressure gauge mounted in your chamber so you could see no just the pop-off pressure but also the pressure drop as well.

No clue and I don't have an accesible gauge that reads high enough. I can tell you though that on my previous version, the piston was popping at 80psi, dropping to 60psi when it was closed again.

You mention your porting's too big, why not drill and tap down into your current porting, screw in a bolt witha rounded off end, and then adjust this in and out to get the best rate of flow (or of course make yet another new one, and fit a ball valve in between chamber and valve)?

I want to change all the parameters - smaller porting, piston seat and piston diameter, in order to make it more efficient. If you restrict the outlet while keeping the same piston seat size, the piston will stay open for longer and you'll still get wasted air. Also, by using a smaller seat I can attempt to use it at 800 psi without an exageratedly compressed spring

It'd also be interesting to see whether differences in expansion chamber volume change the behaviour, but off the top of my head I can't think how to make a variable volume expansion chamber.

I'm going to go with a guestimate, a bit smaller than the current one. Really it's something which you can control by the amount of flow into the chamber.

[psycix]

boerenlul

You should consider yourself lucky that I post all my failures in such a manner that others can learn from my mistakes

You do indeed, and that is something I respect.

I wanted to chrony it but someone, in his endless overenthusiasm, abused the device before the epoxy had full cured and now the valve-tank fitting has come loose, so it needs to be repaired. In the meantime I'll start the smaller version.

*Sigh*

[inonickname]

Yes, it seems that the failboat is failing off into the distance..



Or not..

How high can you turn up the reg on the hpa tank? is 500 the max..

[jackssmirkingrevenge]

How high can you turn up the reg on the hpa tank? is 500 the max..

It has a number of shims you can add or remove from the reg spring, for the following pressure ranges:

High - approx 850 psi

Medium - approx 650 psi

Low - approx 500 psi

I'm currently working with all shims removed so it's in the low range.

[jackssmirkingrevenge]

Update, v4 is ready and curing. I took the opportunity to document the internals before commiting them to their epoxy casket: