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SBA800 - Chaos Edition 4/5/09 updated - Stock

Built a pneumatic cannon? 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: mark.f » Sat May 02, 2009 7:24 pm

POLAND_SPUD wrote:JSR will comment on excesive pilot volume... it's an unwritten rule


Don't you people realize that he can't see the threads if you don't mention his name!?!?!?
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Unread postAuthor: chaos » Sat May 02, 2009 8:13 pm

Hotwired wrote:
Hotwired wrote:You'll be back

Even if it takes a year or so, free time and memories will sneak up and ambush you, dragging your fingers to the keyboard to type out spudfiles in google just to see how things have got on.


:)

It seems to have been shrunk somewhat, gone off marbles?


Yep, down to 6mm a bore and yes its getting smaller.
And screw your nostalgic view almost situation identical prediction haha,


JSR can criticize all he wants, my piston is double o-ringed and thus doesn't give 2 sh!ts about its pilot volume and will always fire.

I have now just "acquired" a rifle stock, so if i continue i'll mount it on that.
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Unread postAuthor: jackssmirkingrevenge » Sat May 02, 2009 8:19 pm

mark.f wrote:Don't you people realize that he can't see the threads if you don't mention his name!?!?!?


Did someone say :!: excess pilot volume :!:

:shock: :shock: :shock:

Some people prefer ergonomics over performance, what can you do?

One thing I don't understand is the reluctance to place the pilot valve directly at the piston outlet, then trigger it removely using a rod, cable, hydraulic unit of what have you, as opposed to most peoples' solution of putting the valve in the grip then plumbing it all the way to the piston.

JSR can criticize all he wants, my piston is double o-ringed and thus doesn't give 2 sh!ts about its pilot volume and will always fire.


Ah, but as the pilot volume is bigger, for a given pilot valve the pressure will go down at a smaller rate and therefore the piston will open slower.
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Unread postAuthor: chaos » Sat May 02, 2009 8:37 pm

jackssmirkingrevenge wrote:
Ah, but as the pilot volume is bigger, for a given pilot valve the pressure will go down at a smaller rate and therefore the piston will open slower.


Ok, i have a proposition for you then, if* and only if i continue with this build, and mount it in the stock, i shall attempt to make a hammer valve to trigger the piston which will take pilot volume back to a bar minimum (as behind the piston is back filled with epoxy) and that should keep you happy yeah? We're talking about 20 cubic millimeters of pilot volume after this is done.
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Unread postAuthor: jackssmirkingrevenge » Sat May 02, 2009 8:48 pm

chaos wrote:that should keep you happy yeah?


The idea is that you'll be happy with the increased performance and reduced pumping effort ;)
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Unread postAuthor: inonickname » Sat May 02, 2009 8:52 pm

Sure you can say that you'll place the valve straight at the piston, but then you run into another problem. While I agree with your use of a hammer valve (and encourage it) you may find that the washer handle has so much more flow you don't notice a difference.

Still, I reckon a hammer valve is a good idea and shall make the cannon very nice.

Personally, I'm going with a modded blowgun to take 300-400 psi with a setup like jook's co-ax in my comp build.
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Unread postAuthor: jook13 » Sat May 02, 2009 9:20 pm

As with your past efforts, this is a very sexy effort. Your breach load is one of the nicest I have seen. I dont think pilot volume makes too much of a difference as long as it not excessive and the piston is a good fit. Look at the QEV. I have had my QEV accidentally cannon fire from disconnecting my shcrader and a tiny bit of air leaked.

I am looking forward to seeing what it looks like with a stock.
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Unread postAuthor: brplatz » Sat May 02, 2009 10:05 pm

This gun is most definitely the sex.
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Unread postAuthor: Ragnarok » Sat May 02, 2009 10:50 pm

jackssmirkingrevenge wrote:One thing I don't understand is the reluctance to place the pilot valve directly at the piston outlet, then trigger it remotely

Let's be honest, that's something else to build - or something else to go wrong.
Of course, you could sort of consider QEV piloted pistons to be something of a sub-sect of that - QEV where it needs to be, QEV's pneumatic trigger where you want it, given that the small differences in pilot opening time that result as a result of the QEV pilot volume will have minimal effect on the main valve's opening time.

That said, I am trying to work out a feasible method of doing something like that for HEAL 2 (which has enjoyed further delays - the universe is conspiring against me, I'm certain), where the valve triggering the QEV is spring loaded, to try and ensure maximum consistency between shots. Not sure it's necessary though.

Ah, but as the pilot volume is bigger, for a given pilot valve the pressure will go down at a smaller rate and therefore the piston will open slower.

Not necessarily, as I've said before. Overly small pilot volumes can actually have a negative effect due to the piston's movement adiabatically heating the air behind it, which is an effect which is related to percentage volume changes. This heating can therefore affect the pressure differential and net force on the piston.
It's actually better therefore to have a modest pilot volume than a "this is only just big enough" one. I stress - the perfect amount is not the smallest volume you can possibly get away with.

And like I've also said before - the difference in end performance between a 0.5 ms opening piston valve and a 4 ms piston valve is completely inconsequential to even the craziest of chronograph addicts. Heck, the difference under the circumstances I modelled was less than the inherent accuracy in any common commercial chronograph I can think of.

I'm not kept around here just because I'm a pretty face*, I do make some effort to try and pass on the scientific theory behind these things, and correct any spudding myths I come across.

*Actually, I'll let you in on a secret. I'm not kept around at all because of my looks. Nobody has ever cited my appearance as a reason they have interest in my continued posting on this site.

~~~~~

I would say something about the launcher, but there's not exactly anything I can say without sounding like I'm repeating something someone else has already said...
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Unread postAuthor: Lentamentalisk » Sun May 03, 2009 1:56 am

If not the end speed results then, the nearly double length pumping time should be a major deciding factor...

Very nice job though.
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Unread postAuthor: jackssmirkingrevenge » Sun May 03, 2009 2:08 am

Ragnarok wrote:I'm not kept around at all because of my looks. Nobody has ever cited my appearance as a reason they have interest in my continued posting on this site.


Actually, your resemblance to British royalty (ignoring the dubious provenance :roll: ) does add a touch of class to the place :D

I know we've debated this before, and yes, perhaps the pilot volume equivalent of a C-string isn't a good idea - but you don't want the granny panty equivalent either, in the case of chaos' launcher the pilot volume seems to be almost the same as the chamber volume, it it's not hurting performance then it's certainly doubling the effort needed to bring it to pressure, and anyone who's ever used a shock pump knows that it isn't a good thing.
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Unread postAuthor: chaos » Sun May 03, 2009 3:14 am

jackssmirkingrevenge wrote:
Ragnarok wrote:I'm not kept around at all because of my looks. Nobody has ever cited my appearance as a reason they have interest in my continued posting on this site.


Actually, your resemblance to British royalty (ignoring the dubious provenance :roll: ) does add a touch of class to the place :D

I know we've debated this before, and yes, perhaps the pilot volume equivalent of a C-string isn't a good idea - but you don't want the granny panty equivalent either, in the case of chaos' launcher the pilot volume seems to be almost the same as the chamber volume, it it's not hurting performance then it's certainly doubling the effort needed to bring it to pressure, and anyone who's ever used a shock pump knows that it isn't a good thing.


Looks are deceiving jack, the pilot hose although long is only 5mm inner diameter. It is triple braided stainless steel hydraulic line, although a bit overboard its all i had at the time to handle the pressure.

Personally, I really think that pilot flow is important than the volume. But that is just me, and im not want an involvement in this spudfiles drama IN MY THREAD FFS!!!.

thanks for all the feedback guys, i have again made the chamber smaller today, milled out the rifle stock, and begun mounting it. Still not 100% sure what im gonna do with the pilot atm, but i guess ill cross that brisge when i get there.
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Unread postAuthor: inonickname » Sun May 03, 2009 3:15 am

jackssmirkingrevenge wrote:
Ragnarok wrote:I'm not kept around at all because of my looks. Nobody has ever cited my appearance as a reason they have interest in my continued posting on this site.


Actually, your resemblance to British royalty (ignoring the dubious provenance :roll: ) does add a touch of class to the place :D

I know we've debated this before, and yes, perhaps the pilot volume equivalent of a C-string isn't a good idea - but you don't want the granny panty equivalent either, in the case of chaos' launcher the pilot volume seems to be almost the same as the chamber volume, it it's not hurting performance then it's certainly doubling the effort needed to bring it to pressure, and anyone who's ever used a shock pump knows that it isn't a good thing.


I'll +1 to that. A shock pump is veeery slow. About the only thing you can call a shock pump fast at is pumping up a pen gun.

Just less pumping would be good.. Also you could do something with the air you're saving, like make a compact co-ax grenade launcher, secondary chamber, flux capacitor, net shooter..
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Unread postAuthor: AdiabaticManiak » Sun May 03, 2009 4:45 am

LOVELY! A well build cannon!

is it hard to pump? I imagine there´s quit limited space for the really hard strokes and such.

edit: keyboard making fun of me
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Unread postAuthor: inonickname » Sun May 03, 2009 4:50 am

AdiabaticManiak wrote:LOVELY! A well build cannon!

is it hard to pump? I imagine there´s quit limited space for the really hard strokes and such.

edit: keyboard making fun of me


Probably not. Shock pumps have a very small bore (and stroke >:() so they aren't even that hard to pump even at pressures like 300 psi. If it is secured to the frame well it would be infact be quite easy to pump.
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