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Performance enhancement

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Performance enhancement

Unread postAuthor: Ragnarok » Sun Dec 07, 2008 8:52 pm

Now, as I'm sure you know, HEAL 2/3vo has been in the pipeline for ages, and has been repeatedly pushed further and further back.
I suddenly snapped this morning after too long without building and started drawing up a list of parts I need to order for the first stage of construction, and I'm hoping to order and build over the Christmas break.
This first stage won't include the semi-auto function, so externally, it will be pretty similar to HEAL - internally... no.

I'm feeling fussy, and I want to try juicing even more power and efficiency from the launcher, so absolutely everything is going to be tightened up: Pilot and dead volumes - especially dead pilot volume (the parts of the pilot volume the piston never moves into), all to be brought down so hard that it'll crack the floor.

Now, as I'm sure most of you know, HEAL has an overbored piston valve, the basic principles of which can be seen in this quick-arse sketch.
The basic principle of this is to maximise flow and minimise opening time, and indeed, it gives HEAL a very respectable performance.
(It might seem odd, but the flow restriction from the internal chamfer, being a smoother transition, is much less than that at the sealing face, making it a worthwhile addition)

That valve design got good results, so it's going to stay for now.

Now other than just more careful construction than before and being ultra petty over stuff to keep things good, there are a few other things I'm considering.
Firstly, I'm planning on internally modifying the fittings with an epoxy putty to eliminate hard edges and thus flow eddies. I'm hoping that doing this will improve internal flow and consequently performance at high velocities.

The breech loader which will be present on the first incarnation will feature probably HEAL's most requested upgrade - an O-ring seal. Not sure how necessary it is, I'm not getting leaks on the current version... but it might make a difference, so I'm adding it.

At the same time as the launcher work, I'll also be making modifications to my high pressure pump, which should make it capable of more pressure again, but with less wear. I'm altering it's intake characteristics so that it cools itself as it's pumped, which should make the seals last longer, and also make it more efficent.
Something I'm half considering, but am unsure of the virtues of, is the use of a filter to remove any solid particles from air being pumped into the chamber.
This will probably be of no noticeable benefit under most circumstances, but it might make a minor difference at high velocities... but I have no idea by how much, or if even at all. I can't see it being a bonus, but I don't know.

That's most of the technical side. In case you've forgotten since I last mentioned it, I'm aiming for a 500 psi pressure limit, just so I can get myself back in-line with the forefront of the high pressure crowd. There will also be a later addition of a semi-auto loader, but I want to sort the basics of things first before fussing with that.

Now, what I'm really looking for opinions on are the concepts of the reduction of internal hard edges and the air filter concept, because I got enough suggestions for additions in this old thread... but if you must suggest more ideas, shoot, this is probably the last chance you'll get.

~~~~~

I've also finally decided on a name to replace the 3vo moniker.
I had thought that Trojan would be nice, but for two fairly big problems I was pretty certain JSR would pick me up on:
1) Monty Python's Trojan rabbit.
2) It's the name for a brand of condoms.

As such, said name has been shot. I have picked a replacement, and I have checked pretty thoroughly that it's not used by any other spudgun, or inappropriate product.
However, you'll have to wait to find out what it is. :twisted:
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Unread postAuthor: VH_man » Sun Dec 07, 2008 9:05 pm

1. I dont understand how the "quick sketch" you posted is of a piston valve.... I see no pilot Volume... Only Chamber.

2. As for The air filter, I think that with all the mechanical parts on a spudgun, Its a good idea. You see them on air compressors correct?

3. As for the "smoothing" of edges, I think youll find that it really wont do anything, But hell, Do it anyway. HEAL is built for riddiculous efficiency.

4. name it the Spartan. Because

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THIS IS SPARTA!

Sorry, I couldnt resist :oops:

But in All honesty, Whats more Hardcore and efficient than a spartan? They nearly defeated the entire persian army with an army of 300. Efficiency at its greatest.
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Unread postAuthor: Ragnarok » Sun Dec 07, 2008 9:15 pm

VH_man wrote:1. I dont understand how the "quick sketch" you posted is of a piston valve.... I see no pilot Volume... Only Chamber.

The piston isn't shown, I was far too lazy to create a silhouette of the bolt piston design I use. You're just seeing the fixed copper components of the valve - right is barrel, left is pilot, down is chamber - piston should be in middle.

You see them on air compressors correct?

You do, but I'm not thinking in terms of launcher life. I'm wondering whether removing said particles from the compressed air will have any performance advantage. I strongly suspect not, but it still niggles at me.

I suppose I don't need to spend any real money on the concept - worst case scenario, I create something out of a fine fabric that filters the air going into the pump.

As for the "smoothing" of edges, I think youll find that it really wont do anything

It might not - but if I'm getting close to supersonic, every hard edge will count.
Eventually I'll put it up against HEAL in a velocity shoot off, see how much the differences are worth.

Name it the Spartan.

Tempting... but not exactly original.
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Unread postAuthor: Gippeto » Sun Dec 07, 2008 9:18 pm

I believe the sketch is showing the intake for the barrel.

The irony.

That was the modification I just made to my bb launcher.

About 12 degrees? :)
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Unread postAuthor: Ragnarok » Sun Dec 07, 2008 9:36 pm

Don Gippeto wrote:I believe the sketch is showing the intake for the barrel.

Indeed it is. You can see it part way through construction here - and here.
It was somewhat messy at that time, but it was later cleaned up significantly.

It's not a very drastic overboring, but I think it gives the valve's flow area an improvement of about 20%. With the subsequent choke on the narrowing, I'd guess it gave the valve a 10%-15% flow boost.

The irony. That was the modification I just made to my bb launcher.

Sorry to steal your thunder on that one.
I think I was originally inspired to it by a post on UKSGC. It increases opening force and flow, so it seemed worth the effort.

About 12 degrees?

About that, yes. I wasn't overly precise about it when I did it - which was about 18 months back when I was somewhat less skilled, so I'm hoping to get better results when I redo it this time. I also have a couple more ideas I hope to exploit to improve the flow at the valve - again, to do with hard edge elimination.
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Unread postAuthor: Gippeto » Sun Dec 07, 2008 9:52 pm

The idea of a nozzle to speed up or slow down flow has been around longer than we have.

No thunder stolen. :)

By "hard edge elimination", are you hinting at maintaining boundary layer attachment? (drag reduction)
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Unread postAuthor: Ragnarok » Sun Dec 07, 2008 10:14 pm

Don Gippeto wrote:By "hard edge elimination", are you hinting at maintaining boundary layer attachment? (drag reduction)

Basically, yes.

Hard/sharp edges in flow cause eddies and increased air drag. By making the flow transitions smoother, I'm hoping to see improvements in performance across the board, but especially in the transonic and near supersonic range.
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Unread postAuthor: FordGtMan » Mon Dec 08, 2008 12:56 am

What are you thinking about making the piston out of? If your going for extreme efficiency with all those modifications, that piston i would think better be light as hell or else it would be a waste in my opinion, but im not sure. Why not take a crap knife and scrape all the excess copper off the tubes left from the pipe cutter instead of the putty? I actually think they make tools for this for better flow with copper pipes. I dont know what they are called though.
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 1:39 am

FordGtMan wrote:Why not take a crap knife and scrape all the excess copper off the tubes left from the pipe cutter instead of the putty?

That's not what I'm talking about. I personally cut my pipes with a mitre hacksaw, which leaves clean, square and unobstructed ends on the pipe, unlike a pipe cutter.
Copper pipe fittings are internally shaped in a way that does not sit flush with a square end on the pipe. This means that there are flow diameter changes and hard edges exposed - even on a perfectly cut pipe end - through fittings, and thus flow eddies. I intend to use a putty to fill any flow diameter increases above the normal pipe bore, and thus get a cleaner flow through a single diameter... if that still makes no sense and you're really stuck, I'll make a diagram.

I'll probably make one anyway, but I'm tired now, so I won't.

If your going for extreme efficiency with all those modifications, that piston i would think better be light as hell

Piston weight is fairly insignificant in what I'm going for. The opening time of the piston is already fast enough that even if I halve the weight of the piston, GGDT gives no difference in the muzzle velocity.

HEAL's piston (a clone of which will be used) is moderately heavy at roughly 60 grams, but that's because it needs to be built sturdily - even as solid as it is, it's slowly been deforming under the forces on it. 3vo will be even more violent.
The high pressures and valve design generate forces on the piston that render it's weight pretty insignificant.
If I could get my hands on the right aluminium parts, I would be only too happy to be able to use that instead of steel... but that's not that important.

I'm not focusing on valve opening time - that's already nearly as good as it can be, and even if it improves, the results are neglible. I'm looking at internal flow improvements, which are not as good as they can be.

In a spudgun, the three big factors are valve opening time, maximum flow and pressure - and to be frank, opening time is actually part of the flow point.

I've got valve opening time and pressure essentially as good as I can manage. Flow isn't bad, but I can improve it, so I will.
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Unread postAuthor: psycix » Mon Dec 08, 2008 12:22 pm

I think smoothing the edges is a very good idea to give a high end launcher that few extra m/s.
Besides that, I would look into gettting a barrel that is smooth; not very smooth, but REALLY smooth: a tight tolerance and maybe some sort of coating.

EDIT:
Ever thought about cheap light pistons that will survive a few shots and get thrown away and replaced?
(for the uber shots) :)
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Unread postAuthor: ALIHISGREAT » Mon Dec 08, 2008 12:37 pm

are you planning on keeping the 'famous' bend in the chamber? or will that reduce performance?

oh and what will you pilot with?
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 1:17 pm

psycix wrote:Besides that, I would look into getting a barrel that is smooth; not very smooth, but REALLY smooth.

I'm planning on polishing, and then if I can sort it, Teflon coating the barrel interior. I might get fussy enough to do the same for the chamber.

Single shot ultra light pistons would be very tricky, but I'll take a look at it.
Really, I think if I could make an aluminium piston, that's as good as I'd ever need.

ALIHISGREAT wrote:Are you planning on keeping the 'famous' bend in the chamber? or will that reduce performance?

It's not going to do the performance any good, but I'm planning on keeping it, mostly because other design factors are dependent on it - partly because it makes the cannon more ergonomic.
If I were that seriously fussy, I'd have a vertical chamber going straight down from the piston valve to have as few bends as possible.

The pilot will be a 1/2" QEV as before, but this time modified somewhat. :twisted:
I'll also be improving the piloting for the 1/2" QEV pilot.

... ARGH, recursion! :shock:
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Unread postAuthor: psycix » Mon Dec 08, 2008 2:31 pm

I'm planning on polishing, and then if I can sort it, Teflon coating the barrel interior. I might get fussy enough to do the same for the chamber.

Now that's what Im talking about! :D

What about wear on the teflon coating?
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Unread postAuthor: Ragnarok » Mon Dec 08, 2008 2:59 pm

psycix wrote:What about wear on the teflon coating?

If I can do it once, I can refinish the barrel interior and recoat it every couple of hundred shots.
The coating inside the chamber (if I decide on it) shouldn't see any wear, so that will be of lesser concern.

In the ideal world, I'd be using <a href="http://en.wikipedia.org/wiki/BAM_(material)">BAM</a>, a recently discovered ceramic alloy that's the third hardest material known to man after diamond and cubic boron nitride (and thus effectively completely wear proof), as well as having only 40% of the friction coefficient of Teflon.

... Thing is, when I say recent, I mean it. The media announcements were all within the last month.
But it is going to be a big thing in the world of materials. It would be one hell of a compound to replace diamond edge tools, because it's almost as hard, next to frictionless, and a lot cheaper.
And like I suggest, it wouldn't go amiss as a gun barrel lining - more velocity, and massively less barrel wear.
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Unread postAuthor: ALIHISGREAT » Mon Dec 08, 2008 3:41 pm

Modified 1/2" QEV?!?! what much can you do to improve it?

maybe an electronic trigger would be good? a mini-solenoid to pilot the QEV? although that could be relatively expensive.
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