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Second cannon, looking for BIG improvements.

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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Second cannon, looking for BIG improvements.

Unread postAuthor: Brad1895 » Sat May 10, 2014 11:53 pm

As this is my first post, I should give you all a quick back story. A few years back I made a simple 3", ball valve, piece of junk. It couldn't pass 50 feet with anything I loaded it with. So now, I'm looking to make a BIG impression on the neighbors. I plan on firing nerf pocket vortext footballs. I know this will sound overkill, but I want the BEST possible range, power, ect. A 5 foot long 2" barrel powered by a 3 foot long 4" chamber. I think a chamber piston valve would be ideal for this, what do you guys think, what size? Is there a noticeable difference when swapping the piston valve with a sprinkler valve? Eventually, this will be a howitzer for long range airsoft/paintball artillery support. I plan on powering it with an on board air tank that can be refilled by hand so there is a buffer, like an auto loading cannon. So, what's your take on this? I have a budget of $300 max, a massive open field behind me (1000 feet+), access to a machine shop for free, and a plethora of hardware. I would like to use a breach load system to make it easier to remain in cover. One last idea that's on the back burner is to add a quarter inch connection 3" from the end of the barrel to power some kind of auto breach opening system with the extra air. All input is welcome as I am the newbie, and you are masters.

EDIT: I'm working towards an over/under with a breach load. Perhaps using a 4 or 6 in piston.
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Ragnarok » Sun May 11, 2014 3:55 pm

Brad1895 wrote:I know this will sound overkill, but I want the BEST possible range, power, ect. A 5 foot long 2" barrel powered by a 3 foot long 4" chamber.

That probably is overkill. It depends on the valve flow-rate, but very few launchers truly benefit from a 2.4:1 C:B ratio.

Take this diagram, which models one of my launchers:
Image
X axis is C:B ratio (just divided through, rather than presented as a x-to-1 ratio), Y axis is the ratio of muzzle energy to the theoretical maximum (with an infinitely large chamber and infinite valve flow).

The blue line is with a valve that has infinite flow (but, as the x-axis says, without an infinitely large chamber). The red line is the predicted performance with the actual valve. The green line is if the valve diameter were halved.

As you can see, an imperfect (read: real) valve flattens the curve very quickly with high ratios. For the green line, going for a 4:1 ratio rather than a 2:1 ratio would add almost nothing to muzzle energy, but double air use.

Now, this wouldn't be too much of a worry if you had a decent compressor (provided that noise levels weren't a worry, as those would increase with air use), but as you're eventually trying to use this in a paintball game... I'd suggest something MUCH more conservatively sized, as it'll dramatically improve shot count.

Also, as Jackssmirkingrevenge keeps reminding us, the same mass of air at a higher pressure (and, ignoring temperature changes, therefore in a smaller volume) gives more energy:

jackssmirkingrevenge wrote:20 inch chamber at 50 psi - 406 feet per second
10 inch chamber at 100 psi - 537 feet per second
5 inch chamber at 200 psi - 684 feet per second
2.5 inch chamber at 400 psi - 830 feet per second
1.25 inch chamber at 800 psi - 958 feet per second
0.625 inch chamber at 1600 psi - 1006 feet per second


So, a smaller chamber you can comfortably and repeatably fill to 100 psi will give you better results than a big chamber you can only fill to 50 psi. As a general rule, I'd generally stay at less than a 2:1 ratio in a launcher and would prefer to make up the difference in extra pressure. (Eventually, the launcher you see in the graph ended up with a 1.5:1 ratio, but that's partly because it was aesthetically pleasing to have the chamber run most of the length under the barrel).

The downside is that for the same volume a higher fill pressure does impact on the amount of air an onboard tank can supply (before it drops below that pressure, anyway).

That said, whatever you do, absolutely do NOT go over a safe pressure (generous safety margin included) for your construction materials.

I think a chamber piston valve would be ideal for this, what do you guys think, what size?

I'd probably recommend a barrel sealer instead, as they're easier to construct and generally open faster because of the way the areas work.

And the answer to size is "as large as possible". Valve cross-sectional area is very important to flow, and therefore the amount of air that can actually get into the barrel to push your projectile.

Is there a noticeable difference when swapping the piston valve with a sprinkler valve?

Yes. They're slower to respond and lower flow.

One last idea that's on the back burner is to add a quarter inch connection 3" from the end of the barrel to power some kind of auto breach opening system with the extra air.

That kind of gas operation tends to not work well (if at all) at low pressures (and by low pressures, I mean "less than several hundred psi"). Also, that's quite gimmicky when you're on a tight budget.

However, if you really want to, a much better gas operation system for pneumatic spudguns is to just hitch one side of a pneumatic cylinder up to the chamber, and keep the other side under a constant pressure (lower than chamber pressure).
As chamber pressure rises and falls during filling and firing, the cylinder operates in kind.

So, what's your take on this?

In all honesty? If it's legitimate to use on your paintball field (and my guess is it might well not be*, although there was the Tippmann C-3), I'd honestly consider doing it as a combustion instead.

Pneumatics in this sort of size aren't particularly portable because of the sheer air requirements, whereas a modestly sized tank of propane would last hundreds of shots (if not thousands) and make recharging the launcher a considerably faster process.
And at "bike pump" pressures, even a piston valve pneumatic will struggle to outperform a metered combustion with good ignition and a fan - particularly if you make a quick change burst disk holder for it.

*That said, if you're using PVC, it's probably safer to have it as a combustion. Propane does not ignite of its own accord (under normal conditions, anyway), but pressurised chambers are known to go blooey if dropped onto anything hard and/or pointy (such as many rocks that might be found on a paintball field).
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Brad1895 » Sun May 11, 2014 7:51 pm

Ragnarok wrote:
Brad1895 wrote:I know this will sound overkill, but I want the BEST possible range, power, ect. A 5 foot long 2" barrel powered by a 3 foot long 4" chamber.

That probably is overkill. It depends on the valve flow-rate, but very few launchers truly benefit from a 2.4:1 C:B ratio.

Take this diagram, which models one of my launchers:
Image
X axis is C:B ratio (just divided through, rather than presented as a x-to-1 ratio), Y axis is the ratio of muzzle energy to the theoretical maximum (with an infinitely large chamber and infinite valve flow).

The blue line is with a valve that has infinite flow (but, as the x-axis says, without an infinitely large chamber). The red line is the predicted performance with the actual valve. The green line is if the valve diameter were halved.

As you can see, an imperfect (read: real) valve flattens the curve very quickly with high ratios. For the green line, going for a 4:1 ratio rather than a 2:1 ratio would add almost nothing to muzzle energy, but double air use.

Now, this wouldn't be too much of a worry if you had a decent compressor (provided that noise levels weren't a worry, as those would increase with air use), but as you're eventually trying to use this in a paintball game... I'd suggest something MUCH more conservatively sized, as it'll dramatically improve shot count.

Also, as Jackssmirkingrevenge keeps reminding us, the same mass of air at a higher pressure (and, ignoring temperature changes, therefore in a smaller volume) gives more energy:

jackssmirkingrevenge wrote:20 inch chamber at 50 psi - 406 feet per second
10 inch chamber at 100 psi - 537 feet per second
5 inch chamber at 200 psi - 684 feet per second
2.5 inch chamber at 400 psi - 830 feet per second
1.25 inch chamber at 800 psi - 958 feet per second
0.625 inch chamber at 1600 psi - 1006 feet per second


So, a smaller chamber you can comfortably and repeatably fill to 100 psi will give you better results than a big chamber you can only fill to 50 psi. As a general rule, I'd generally stay at less than a 2:1 ratio in a launcher and would prefer to make up the difference in extra pressure. (Eventually, the launcher you see in the graph ended up with a 1.5:1 ratio, but that's partly because it was aesthetically pleasing to have the chamber run most of the length under the barrel).

The downside is that for the same volume a higher fill pressure does impact on the amount of air an onboard tank can supply (before it drops below that pressure, anyway).

That said, whatever you do, absolutely do NOT go over a safe pressure (generous safety margin included) for your construction materials.

I think a chamber piston valve would be ideal for this, what do you guys think, what size?

I'd probably recommend a barrel sealer instead, as they're easier to construct and generally open faster because of the way the areas work.

And the answer to size is "as large as possible". Valve cross-sectional area is very important to flow, and therefore the amount of air that can actually get into the barrel to push your projectile.

Is there a noticeable difference when swapping the piston valve with a sprinkler valve?

Yes. They're slower to respond and lower flow.

One last idea that's on the back burner is to add a quarter inch connection 3" from the end of the barrel to power some kind of auto breach opening system with the extra air.

That kind of gas operation tends to not work well (if at all) at low pressures (and by low pressures, I mean "less than several hundred psi"). Also, that's quite gimmicky when you're on a tight budget.

However, if you really want to, a much better gas operation system for pneumatic spudguns is to just hitch one side of a pneumatic cylinder up to the chamber, and keep the other side under a constant pressure (lower than chamber pressure).
As chamber pressure rises and falls during filling and firing, the cylinder operates in kind.

So, what's your take on this?

In all honesty? If it's legitimate to use on your paintball field (and my guess is it might well not be*, although there was the Tippmann C-3), I'd honestly consider doing it as a combustion instead.

Pneumatics in this sort of size aren't particularly portable because of the sheer air requirements, whereas a modestly sized tank of propane would last hundreds of shots (if not thousands) and make recharging the launcher a considerably faster process.
And at "bike pump" pressures, even a piston valve pneumatic will struggle to outperform a metered combustion with good ignition and a fan - particularly if you make a quick change burst disk holder for it.

*That said, if you're using PVC, it's probably safer to have it as a combustion. Propane does not ignite of its own accord (under normal conditions, anyway), but pressurised chambers are known to go blooey if dropped onto anything hard and/or pointy (such as many rocks that might be found on a paintball field).
Thank you for the info. So It would be more reasonable to cut down the length of the chamber by a foot say? As far as the barrel seal, won't that make a breach loading method impossible. After reading the part about the explosion hazards of pvc, I think I'll just use metal. My dad does tool and die work, so I have access to Mcmaster, grainger, ect.
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Brad1895 » Tue May 13, 2014 6:21 am

Ragnarok wrote:
Brad1895 wrote:I know this will sound overkill, but I want the BEST possible range, power, ect. A 5 foot long 2" barrel powered by a 3 foot long 4" chamber.

That probably is overkill. It depends on the valve flow-rate, but very few launchers truly benefit from a 2.4:1 C:B ratio.

Take this diagram, which models one of my launchers:
Image
X axis is C:B ratio (just divided through, rather than presented as a x-to-1 ratio), Y axis is the ratio of muzzle energy to the theoretical maximum (with an infinitely large chamber and infinite valve flow).

The blue line is with a valve that has infinite flow (but, as the x-axis says, without an infinitely large chamber). The red line is the predicted performance with the actual valve. The green line is if the valve diameter were halved.

As you can see, an imperfect (read: real) valve flattens the curve very quickly with high ratios. For the green line, going for a 4:1 ratio rather than a 2:1 ratio would add almost nothing to muzzle energy, but double air use.

Now, this wouldn't be too much of a worry if you had a decent compressor (provided that noise levels weren't a worry, as those would increase with air use), but as you're eventually trying to use this in a paintball game... I'd suggest something MUCH more conservatively sized, as it'll dramatically improve shot count.

Also, as Jackssmirkingrevenge keeps reminding us, the same mass of air at a higher pressure (and, ignoring temperature changes, therefore in a smaller volume) gives more energy:

jackssmirkingrevenge wrote:20 inch chamber at 50 psi - 406 feet per second
10 inch chamber at 100 psi - 537 feet per second
5 inch chamber at 200 psi - 684 feet per second
2.5 inch chamber at 400 psi - 830 feet per second
1.25 inch chamber at 800 psi - 958 feet per second
0.625 inch chamber at 1600 psi - 1006 feet per second


So, a smaller chamber you can comfortably and repeatably fill to 100 psi will give you better results than a big chamber you can only fill to 50 psi. As a general rule, I'd generally stay at less than a 2:1 ratio in a launcher and would prefer to make up the difference in extra pressure. (Eventually, the launcher you see in the graph ended up with a 1.5:1 ratio, but that's partly because it was aesthetically pleasing to have the chamber run most of the length under the barrel).

The downside is that for the same volume a higher fill pressure does impact on the amount of air an onboard tank can supply (before it drops below that pressure, anyway).

That said, whatever you do, absolutely do NOT go over a safe pressure (generous safety margin included) for your construction materials.

I think a chamber piston valve would be ideal for this, what do you guys think, what size?

I'd probably recommend a barrel sealer instead, as they're easier to construct and generally open faster because of the way the areas work.

And the answer to size is "as large as possible". Valve cross-sectional area is very important to flow, and therefore the amount of air that can actually get into the barrel to push your projectile.

Is there a noticeable difference when swapping the piston valve with a sprinkler valve?

Yes. They're slower to respond and lower flow.

One last idea that's on the back burner is to add a quarter inch connection 3" from the end of the barrel to power some kind of auto breach opening system with the extra air.

That kind of gas operation tends to not work well (if at all) at low pressures (and by low pressures, I mean "less than several hundred psi"). Also, that's quite gimmicky when you're on a tight budget.

However, if you really want to, a much better gas operation system for pneumatic spudguns is to just hitch one side of a pneumatic cylinder up to the chamber, and keep the other side under a constant pressure (lower than chamber pressure).
As chamber pressure rises and falls during filling and firing, the cylinder operates in kind.

So, what's your take on this?

In all honesty? If it's legitimate to use on your paintball field (and my guess is it might well not be*, although there was the Tippmann C-3), I'd honestly consider doing it as a combustion instead.

Pneumatics in this sort of size aren't particularly portable because of the sheer air requirements, whereas a modestly sized tank of propane would last hundreds of shots (if not thousands) and make recharging the launcher a considerably faster process.
And at "bike pump" pressures, even a piston valve pneumatic will struggle to outperform a metered combustion with good ignition and a fan - particularly if you make a quick change burst disk holder for it.

*That said, if you're using PVC, it's probably safer to have it as a combustion. Propane does not ignite of its own accord (under normal conditions, anyway), but pressurised chambers are known to go blooey if dropped onto anything hard and/or pointy (such as many rocks that might be found on a paintball field).
Ok, revised idea. I want to stick with an over/under and rear breach load. Going from a 4" chamber, I moved to a 3" chamber 40" long. The barrel is still 2" x 60". 2" chamber seal piston valve with a sprinkler valve as the pilot. How's that sound?
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: jackssmirkingrevenge » Thu May 15, 2014 4:39 am

Brad1895 wrote:Going from a 4" chamber, I moved to a 3" chamber 40" long. The barrel is still 2" x 60". 2" chamber seal piston valve with a sprinkler valve as the pilot. How's that sound?


Sounds like you will have one heck of a powerhouse ;) your piston cannot be the same diameter as your barrel though...
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Ragnarok » Thu May 15, 2014 5:20 pm

Brad1895 wrote:Thank you for the info. So It would be more reasonable to cut down the length of the chamber by a foot say?

I'd say so. Swapping to your 3" x 40" chamber will give you a notably more efficient C:B ratio. Still not exactly thrifty on air, but much better.

As far as the barrel seal, won't that make a breach loading method impossible.

There are loads of breech-loading barrel sealers. Two common approaches are a moveable barrel - either one that slides forward (while rare in normal firearms, it's used on things like the NS2000 and RMB 93 shotguns) or a pivoting barrel (as used on your favourite break-open shotguns) - or a port in the side of the barrel that gets sealed by a movable sheath.

After reading the part about the explosion hazards of pvc, I think I'll just use metal.

I shouldn't mislead you into believing that PVC is intensely hazardous, but it's not exactly the safest choice for a pressure vessel. It's not hugely strong as a material and it often fails by shattering into shards. (Pointy shards that burn with the fire of a thousand evils*).

*Not that you'll necessarily get the reference...
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Boomer58cal » Thu May 15, 2014 6:09 pm

Is there a noticeable difference when swapping the piston valve with a sprinkler valve?

I just thought I would add my two cents.Image
this is Trinity my second launcher, it has three 1 inch sprinkler valves in parallel. Just as an example, even with three sprinkler valves in parallel, a properly designed 1.5 inch porting piston valve should equal if not outperform it.
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Re: Second cannon, looking for BIG improvements.

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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Brad1895 » Fri May 16, 2014 7:30 pm

So here's my change. I ran into a few issues with the ammo idea. I have a friend that said the smaller nerf vortex footballs are hard to see/find. So, I thought "Why not use the howlers?" The problem being, they are the most odd ball sized projectiles I've ever seen. My idea is to sleeve the barrel. Not sure what to use, but it will have to be 4" in something. This also increases the chamber size to...oh dear, 866 cubic inches. 3.75 GALLONS! Now, that's not going to stop me from filling it. A few highschoolers with some energy, a quad runner, and a backup air pump is all we need. What is good for bringing the barrel diameter down to fit this proj.? It's 3.5 inches roughly, so another piece of 4" pvc, or even some abs would work, right?
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Boomer58cal » Fri May 16, 2014 10:37 pm

Brad1895 wrote:So here's my change. I ran into a few issues with the ammo idea. I have a friend that said the smaller nerf vortex footballs are hard to see/find. So, I thought "Why not use the howlers?" The problem being, they are the most odd ball sized projectiles I've ever seen. My idea is to sleeve the barrel. Not sure what to use, but it will have to be 4" in something. This also increases the chamber size to...oh dear, 866 cubic inches. 3.75 GALLONS! Now, that's not going to stop me from filling it. A few highschoolers with some energy, a quad runner, and a backup air pump is all we need. What is good for bringing the barrel diameter down to fit this proj.? It's 3.5 inches roughly, so another piece of 4" pvc, or even some abs would work, right?


The launcher in my last post has an air chamber capacity of about 335 ci. I have filled it once and only once with a bike pump... it took over 300 pumps( and several minutes ) to reach 100 psi. It will take somewhere around 775 pumps to fill a 866 ci chamber to 100 psi. :shock:

My small 12 volt compressor took even longer. About 10 minutes per shot. My small 1/3 hp 3 gal compressor takes 2-3 minutes. My 65 gal 6.5 hp compressor will fill it about as fast as you can load, fill and fire it.

10 or 15 minutes between shots is just no fun. :cry:
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Brad1895 » Sat May 17, 2014 8:14 am

At these numbers, I'm going to have to use an air compressor tank for the chamber. It would be hard to fit a gigantic piece of pvc instead. No problem. I may use two or three bike pumps for the job, with a compressor as an assist.
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Ragnarok » Sat May 17, 2014 8:41 am

Brad1895 wrote:Now, that's not going to stop me from filling it.

Oh yes it is. To do a quick back of the envelope calculation: For a single stage pump, the absolute maximum sane cylinder volume is about 40 cubic inches (somewhere between 1.5 and 2 square inches cross-section, 24 inch stroke).

That makes the necessary number of strokes at least about 150, which at 3 seconds a stroke (which is an optimistically fast pace to sustain, even with several people swapping) makes for at least seven to eight minutes of pumping to get to 100 psi.

I wouldn't expect much more than six shots an hour. (That said, 100 psi might be more than is safe to use for when it's on a paintball field. That could get a Nerf football travelling lethally fast).
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Re: Second cannon, looking for BIG improvements.

Unread postAuthor: Boomer58cal » Sat May 17, 2014 12:44 pm

You could try 3 shrader valves, 3 hand pumps and 3 energetic high school kids in parallel. You could fuel them with energy drinks :lol:
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