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Just a quick "Hello"

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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Unread postAuthor: High-PSI » Sat Oct 09, 2010 8:05 pm

Hey Guys,

I am a newbie here, though I have 10,000 posts on various other chat rooms for other hobbies.

I have various air cannons built right now (1/2 inch sch 40 barrels) and I am in the process of building a couple larger bore cannons (1-1/4" and 2" barrels). I will post pictures and build threads when I have something decent to show.

At any rate, as my name suggests, I am into high psi cannons. It is amazing what happens when psi exceeds the 200 mark. :D

Again, I will post something interesting as I have pictures. My stuff is kind of unorthodox.

Anyway, I just wanted to chime in and say hello.

I am looking forward to getting to know you all..........

Matt
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Unread postAuthor: Technician1002 » Sat Oct 09, 2010 8:11 pm

Welcome, It will be fun to see what you bring to SpudFiles. Do you have plans for something with high volume for the larger bore cannons? I find amazing things happen when larger bore reaches 100 PSI. Smaller bore cannons seem to need more pressure to perform well.

My large bore at 200 PSI would need tied to a tree to fire it. :shock: The kick with only 100 PSI is plenty.
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Unread postAuthor: High-PSI » Sat Oct 09, 2010 8:48 pm

Currently, I have a couple 1/2 inch barrel guns firing Delrin slugs with a steel tip. At 230 psi one shot will pierce two sheets of 3/4 inch plywood with a clean hole. That is 900fps (9 gram slug) according to my Chrony.

My high pressure guns are all metal. I am using aluminum sch 40 tube (threaded by a plumber friend of mine), welded steel pressures tanks (exhaust tubing for the tank), and brass diaphram valves. I use Granzow fast acting diaphram valves modded with a second 1/2 inch bore Diaphram valve as a pilot valve. Running these valves in two stages is LOUD and extremely sharp sounding. These valves are crazy expensive. But, I get them wholesale, so it is not so bad.

Anyway, my big gun has a 4 foot aluminum 2 inch sch 40 barrel with a 2 inch bore Granzow brass valve (again, modded with a 1/2 inch pilot valve drilled and tapped into the diaphram top cover). The pressure tank is made from 4 inch exhaust tube welded together. Picture the valve resting on my shoulder with the valve at my ear (I know, I know, wear hearing protection) and the barrel in front of me. The pressure tank is made up of the 4 inch exhaust tubing in a 180 degree bend running from the back of the valve behind me, then down under my arm and going between my elbow and my side, then running straight ahead from there. The whole gun is 5 feet long and should weigh in at close to 40 pounds when it is all done. It will have a shoulder stock and padded rest so my shoulder will take all the load.

I have a small machineshop. So, I can machine and weld nearly anything I want. That helps tremendously.

Matt
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Unread postAuthor: BeaverRat » Sat Oct 09, 2010 9:52 pm

Very cool, make sure you post these in the showcase! I just finished up a 3/4" bore high pressure cannon using one of these valves: I too am using a diaphragm valve to pilot the main, it is very loud!

http://www.spudfiles.com/forums/innards ... 21750.html

At 400 psi, it sends a wine cork the speed of sound.
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Unread postAuthor: Gippeto » Sat Oct 09, 2010 11:43 pm

Welcome Matt. :P

Okay, enough with the cheesey jokes. :)

You sound like an interesting guy to have around, I look forward to seeing what ya got.

So....Whatcha got?

Bring on those pictures.
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Unread postAuthor: High-PSI » Sun Oct 10, 2010 7:30 am

BeaverRat wrote:Very cool, make sure you post these in the showcase! I just finished up a 3/4" bore high pressure cannon using one of these valves: I too am using a diaphragm valve to pilot the main, it is very loud!

http://www.spudfiles.com/forums/innards ... 21750.html

At 400 psi, it sends a wine cork the speed of sound.


Wow, a wine cork! Great idea!

The highest muzzle velocity I have seen was with a 5 foot barrel, 250psi, and a 2 gram Delrin slug (libricated). That gave me consistantly 1,723 to 1,749 fps according to my Chrony. That is totally impractical to carry around and use. Besides, that slug is worthlessly tiny and light.

Oh, one cool thing, with the 9 gram slug and a long barrel, the recoil is really something. It kicks like a 9mm handgun. :D

I will try to run to the shop and take one quick shot (or two) to show. The big gun is merely a mostly finished pressure tank with the valve and barrel mounted together. No handles, trigger, shoulder stock or anything else yet. You can get an idea of what it looks like, though.

I wasn't going to join this forum until I had something to show. But, what the heck, I was bored yesterday and figured I may as well sign up. I would assume you get newbies signing on who talk a big game and never build anything. That is not me. I manufacture high-end RC helicopters, completely scratch built RC cars, upgrades for helis, and high-end brushless E-bike conversion kits. I also scratch build bikes and recumbents. I used to compete in SPL car audio as well. That is on top of my full time appliance repair job and home-schooling my kids. I am a busy guy. The free time I have is due to the fact that we do not watch any TV in our home. I would rather build and experiment than watch the worthless garbage on the tube.

Anyway, enough jaw flapping. I will post some pictures of what little I can show sometime this afternoon. :wink:

Matt
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Unread postAuthor: Ragnarok » Sun Oct 10, 2010 8:14 am

High-PSI wrote:That gave me consistantly 1,723 to 1,749 fps according to my Chrony.

I'm sceptical - it's very rare for a pneumatic cannon to beat the speed of sound, and I've never seen it happen by that kind of margin.

The problem is, gases do not normally expand faster than their speed of sound. If you're using regular air (as opposed to a light gas like helium), there have to be some fairly special effects to heat the air and raise its speed of sound - and that pressure just isn't up to that kind of compression heating.
Alternatively, it might be possible that the lubricant you used dieseled upon firing (thus burning and raising gas temperatures), but 250 psi would be marginal for that.

In this case (actually, in just about any case) I'd start by throwing doubt on the chrony readings - if you're too close to it when you fire, the muzzle blast can easily interfere with the readings.
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Unread postAuthor: Gun Freak » Sun Oct 10, 2010 10:51 am

Welcome! I'm anxious to see your cannons and some videos :) What do you use to fill your cannons?
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Unread postAuthor: High-PSI » Sun Oct 10, 2010 12:20 pm

I totally understand the doubt on the muzzle velocity. I was freaked out when I first saw those numbers.

Here is my understanding on what is going on (I have gone over this with a number of individuals specializing in areas of concern here).

The way this began was simple experimentation with PVC parts and a sprinkler valve, as many others have begun. I began experimenting with other valves (that is how I moved toward brass bodied Granzow valves). I began running larger bore valves with barrels that tapered the diameter down to the 1/2 inch barrel. The best results were from a 1" bore valve tapered to a 1/2 inch barrel. This dropped the turbulence down within the valve to sub-sonic levels. At that point, I was seeing 1,050 FPS at 200 PSI consistantly. The next experiment was in lengthening the pressure chamber. This was not for added volume, but as a means to trick the PSI a touch higher. Air weighs 4.7kg (If I remember correctly) per cubic yard. If that air is rushing forward toward the valve, you can achieve an increase in pressure behind the projectile. This is from the smaller diameter but longer chamber creating a higher forward speed of the air (still sub-sonic) toward the valve. The innertia of the air, along with the pressure gave a HUGE increase in muzzle velocity. The problem is, this is a very sensitive ratio, apparently. I fired round after round from various distances and consistantly saw the same velocity. However, after that, I began doing more testing and every other change I made reduced velocity noticeably. So, I found a sweet-spot. However, that sweet-spot is not something I can build and carry around. The darn cannon is 8 feet long! It was merely built as a test bed to see just how fast a projectile can be pushed. Once that information was obtained, I gained a far larger understaning of what is going on with these cannons and I am using that knowledge to build a few truely useable guns. All of those will max at about 800 FPS max, however, and those are the small bore guns. I do not think I could hang onto a 2 inch gun with that much power. I am hoping for 500 fps with my 2" gun.

My primary source of information is a friend who does research (or did in college) on a supersonic wind tunnel. That tunnel is simply a huge air cannon like we use with numerous air flow stabilization steps taken. The key is to keep the flow at sub-sonic levels through the valve, then accellerate the air in the barrel only. That keeps any shockwaves inside the smooth barrel, rather than creating even more turbulence in the valve. That is the primary principal in achieveing high super-sonic air flow in these wind tunnels.

My source of air is a Helix low rider airbag suspension system compressor. I am using lithium polymer batteries to drive it (left overs from one of my E-bikes). :) It is reated at 200 psi. But, I can sneak 250 out of it running at 24 volts rather than 12. It get hot that way, however.

At any rate, super-sonic cannons are not all they are cracked up to be. For one thing, the accuracy goes completely out the window. For another, the velocity drops to sub-sonic leves so rapidly, it is really not feaseable to use unless you can hit extremely high mach numbers. It is far better to stay slighly sub-sonic with the highest weight projectile possible for the intended target.

Bear in mind, I am totally open to my Chrony being wrong. I researched that as well.

I wish I had a way to calculate the pressure (FPS) required to penetrate two sheets of 3/4 inch plywood with a 9 gram .60 caliber projectile. Wether my Chrony is right or wrong, I have way more power than I can really use. :D

Part of me joining this forum is to learn what I can from those who are farther along the path.

Oh, lastly, when I was down in the 850 fps range, I did get one 2,150 FPS reading from my Chrony. I know that was an error. All the 1,700 FPS readings were repeated under various conditions. Again, I am open to it being wrong, however. Hey, maybe two chronographs in a row would be good for redundancy?

Matt
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Unread postAuthor: Ragnarok » Sun Oct 10, 2010 1:36 pm

High-PSI wrote:I totally understand the doubt on the muzzle velocity. I was freaked out when I first saw those numbers.

Sorry, but I've been doing more thinking, and I can say your explanation cannot possibly be the reason. The cannon would actually be breaking the laws of thermodynamics to do reach those energies in that barrel without an additional source of energy.*
*I may have overlooked something, but my physics knowledge is hardly shabby.

The only place I can guess this might come from is dieseling of the lubricant. I wouldn't be surprised if changing to a non-flammable lubricant (such as silicone oil) meant the velocity dropped massively.

... that is assuming the chrony hasn't been fooled, of course.

Air weighs 4.7kg (If I remember correctly) per cubic yard.

It's about 1.2-1.3 kg per cubic metre. Per cubic yard, it would be about a kilo at max.
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Unread postAuthor: High-PSI » Sun Oct 10, 2010 1:50 pm

Ahh, good.

You may be 100% correct on the deiselling. That would explain alot! For one thing, it would explain the extreme noise level increase on those shots. I know about deiselling from air rifle sites, but never applied that to my cannons. Hmm, I need to think more outside the box.

Thanks for the info! :)

Matt
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Unread postAuthor: Ragnarok » Sun Oct 10, 2010 2:08 pm

High-PSI wrote:I know about deiselling from air rifle sites, but never applied that to my cannons.

Well, 250 PSI would be a pretty low dieseling pressure, but it might about be enough if everything else was just so and the lubricant particularly volatile.
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Unread postAuthor: High-PSI » Sun Oct 10, 2010 4:26 pm

I appreciate the info. I may be alot of negative things, but I can tell you (on the positive side) I am teachable.

Sometimes, at least in my case, it seems the lack of folical cells also reduces the overall brain capability. :wink:

Anyway, I need to get some pictures up!

I am glad there are others who have done this stuff longer than I and have a better grasp of physics in general. I am a mechanical problem solver, not a physicist.

Thanks, again!

Matt
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Unread postAuthor: Technician1002 » Sun Oct 10, 2010 5:04 pm

Instead of a second chronograph, pick up a high speed camera.
This was shot at 1,000 frames/sec. The orange is a little slower than a foot a second. Chrony shows it just over 600 FPS. Youtube tended to drop a few frames in the upload. At the far right it looks like a foot a sec, but it's only slowed to about 500.
[youtube]http://www.youtube.com/watch?v=jAoXj9Ku0s0[/youtube]
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Unread postAuthor: High-PSI » Sun Oct 10, 2010 6:06 pm

Very cool!

Matt
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