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40mm Rubber Bullet gun VIDEO UPDATE

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: Ragnarok » Tue May 12, 2009 9:38 am

@rikukiakuchiki777: The valve on this is somewhat more sophisticated than the average valve. It's a positive acting piston valve (almost all valves on this site are negative acting), which as far as I know, has very little literature on this site dedicated to it. Mostly because there are so few things that use it.

This is not exactly how it works, given that these pictures all depict negative acting valves, but check out this topic anyway:
Piston valves explained visually

jagerbond wrote:Thanks for the Helium info.

Handing out lots of information is what I do best.

I see the specs say 50-1200PSI what velocities have been achieved? Have any other gases been experimented with at higher velocities?

For the Eclipse's normal tasks, an excess of velocity could actually be detrimental.
As inonickname points out, less-lethal launchers are Solar's "weapon of choice". Not that I'm keen on using the word "weapon", but I am keen on making references.

I can't currently answer either of those questions accurately, but at 1200 psi, I would be highly surprised if certain projectiles couldn't be pushed past 1000 fps with air.
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Unread postAuthor: CpTn_lAw » Tue May 12, 2009 9:42 am

I agree with Rag, 1200 psi is a lot of pressure...1000 fps is achievable with far less pressure than that, so i think it'd be entirely possible.
And thanks for the helium info; i knew that SoS is around 1300 m/s at 27°c, but the actual difference in projectile velocity past 150m/s, that i didn't know.

I assume a lot of launchers here could benefit from pressurising with helium instead of air, as a lot of these launchers tend to push projectiles past 150 m/s
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Unread postAuthor: Ragnarok » Tue May 12, 2009 10:55 am

CpTn_lAw wrote:I agree with Rag, 1200 psi is a lot of pressure...1000 fps is achievable with far less pressure than that, so i think it'd be entirely possible.

Yes, but the Eclipse has a reasonably high bore and short barrel, which makes it much harder to achieve a given velocity.

As projectile mass scales as the cube of the barrel diameter, then a doubling in barrel diameter takes 8 times the force to reach the same velocity (with a projectile of a given shape and density).
Fortunately, force from pressure scales with the square of the barrel, so in this case, 4 times the force at the same pressure.
However, that leaves us falling behind by a factor of two, so the Eclipse needs twice as much pressure to achieve a given velocity with the same shape and density projectile as would a 20mm launcher with the same barrel length.

To bring HEAL into this briefly (being an example of a 20mm launcher that achieves high velocities) - its barrel is around twice as long as the Eclipse's, which then calls for the Eclipse to double it's pressure again to keep up.

So basically, 1200 psi in the Eclipse is roughly equivalent velocity-wise to 300 psi in HEAL. You can't neglect the importance of launcher dimensions to velocity.

And thanks for the helium info; i knew that SoS is around 1300 m/s at 27°c, but the actual difference in projectile velocity past 150m/s, that i didn't know.

Actually, at typical temperatures, Helium's SoS is about 1000 m/s. It's Hydrogen that has the 1300 m/s SoS.

The difference after 150 m/s is about when helium's disadvantageous ratio of specific heats (henceforth RoSH) starts to be cancelled out by it's lower density (and thus lower momentum, detracting less from the energy of the projectile.)

Interestingly, it's helium's high RoSH that makes it's SoS relatively close to that of hydrogen's. SoS is proportional to the square root of the RoSH, so with a RoSH of 1.4, it would have an SOS of closer to 920 m/s.

I assume a lot of launchers here could benefit from pressurising with helium instead of air, as a lot of these launchers tend to push projectiles past 150 m/s

The change is still fairly minor at 150 m/s - you'd need to start to push beyond that a bit before it would become a meaningful change.

On a similar note to above, hydrogen is the real "Ultimate gas". Lighter than even Helium; a RoSH of k=1.41, so about the same decompression efficiency to air; and a very good specific heat (Cp = 14.15 kJ/kg/K).

Obviously, air beats it by being non-flammable and being more available, but for sheer performance, hydrogen is epic. If I could produce it efficiently and in large amounts, you could bet I would be using it for occasional shots with my cannons...
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Unread postAuthor: CpTn_lAw » Tue May 12, 2009 11:12 am

I think hydrogen has a great future ahead in many, many uses. The potential energy it release when properly excited is tremendous; working on it right now for my quantum mecanics exam (tomorrow).

Thanks for corecting me, i mixed up the two SoS ^^
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Unread postAuthor: Leonard » Tue May 12, 2009 4:12 pm

Positive acting piston valve? Something like those paintball "spool valve" marker where the piston exhaust volume is in front of it, so it goes forward when air is exhausted? (and thus pulling the bolt forward at the same time?)

I'm just realy confused as how semi-auto is achieved if it is a piston valve.

EDIT : Sorry, I dont mean to highjack the thread, i'm just curious.
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Unread postAuthor: Solar » Tue May 12, 2009 4:21 pm

The o-rings of the Eclipse are rated to 1200psi. I have not incorporated the higher pressure triggering system yet and the main valve need a shim to allow it higher than 600psi since these first ones do not have a molded rubber stopper and instead use a piston and o-ring that slides into the valve opening to make a seal, moving the pressure back onto the rear valve cap. This was a change that the CAD guy made right before the parts were run. I argued against it, but was convinced it was ok.

The barrels and ballast chambers can be swapped to longer ones that increase the power. I can achieve the same results at 150psi as with 300psi if I use the proper ballast chambers.

Regarding lethal/less lethal, the military is looking for the next level... I have crossed over. 23 grams at 350fps achieves lethal foot pounds I believe. I will have some number later today. My x-radar chronograph wasn't up to the task, I will be getting my other one today.

I made a few vids, but can't find my cable to transfer them. I will get a new one today so I can share.

The main firing valve uses a larger diameter piston in the back of the main valve that is unpressurized until the trigger is pulled. As the pressure is rising to firing pressure (about half the working pressure with the ratio I am using(think shock pump)) the line is tapped for the bolt piston, which has enough time to close before the launcher fires.
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Unread postAuthor: CpTn_lAw » Tue May 12, 2009 4:34 pm

130 joules, not bad at all!! NATO standards say 85 joules is lethal if hit in a sensitive area...
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Unread postAuthor: Hotwired » Tue May 12, 2009 5:22 pm

Energy isn't everything, some girl in a protest died after getting a pepperspray projectile in her eye from a less lethal FN303 launcher - which is more or less the same theme as the Eclipse (pneumatic semi, drum mag) but for little paintball sized pellets.


Why did you lose the drum mag for the rubber balls by the way?
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Unread postAuthor: Ragnarok » Tue May 12, 2009 6:10 pm

Hotwired wrote:Why did you lose the drum mag for the rubber balls by the way?

Cost, weight and ammunition capacity I'm guessing.

@Leonard: There's nothing stopping something being semi-auto if it's a piston valve. It just needs an external gas supply.
It's still semi-auto, just not self contained semi-auto.

When I say positive acting, most piston valves work by venting a pilot volume, meaning that they work on a lack of pressure somewhere in the system.
Positive acting means the reverse. There is a part of the system which must be pressurized to open the valve. This is safer, but more complex to achieve, and may cause other issues.

Anyway, you might be interested in this old topic of Solar's, with some valve pictures and diagrams in it.

@Solar: Although those energies are certainly potentially lethal if it breaks the skin, I recall this video of yours.

You report the weight about 26 grams, and based on all the information present....

Feeding those numbers into latest version of the LRC, my best estimations predict that projectile's velocity in the vicinity of 400 fps at impact (Between 380 and 420 fps, anyway). That puts the impact at a painful 140 ft-lbs, which is more than you're talking about here, and I'm pretty sure your cameraman survived.

Certainly briefly incapacitated, but not dead. If you're looking for lethal, you're gonna need a bigger boat.

If you're looking for definite incapacitation, with a chance of lethality acceptable, then I'd say you're probably in the right region.
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Unread postAuthor: Solar » Tue May 12, 2009 7:30 pm

Some initial chronograph testing was most likely in error and that video was a guess at the distance, using the number of frames at 30 frames per second to calculate time. However a muzzle velocity is different than the velocity at impact, you are correct. The foam rocket was also FOAM... the rubber rounds are the same weight almost but quite a bit more condensed and different durometer. I am waiting for my chrono to show up and will get some data posted tonight I hope.

Regarding the positive force piston valve, I have had no issues with it other than continued happiness. It can use the ballast pressure and can also be used inline with other pistons to drive any mechanism needed.

The reason I made this version was to work my way to a semi-auto bolt for the standard Eclipse as well. Also I am going for accuracy and the mini tennis balls are more consistent in weight than the hand made finned rounds until we get a full size industrial mold operational with check valves and temperature control. I just weed through the bags of balls with a scale to sort them.

The interest in my launcher also stems from the FN303 fatality since these rounds are too big to penetrate an eye socket or to fit between ribs.
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Unread postAuthor: Solar » Tue May 12, 2009 7:37 pm

http://www.humphrey-products.com/hpwpc. ... IDGE06.pdf


The Y500IN version of this valve is what I used on earlier, less powerful launchers. The Eclipse valve is like a jumbo one of these. The PDF goes into the operation and mounting. This one can also be used with an extra exhaust that was eliminated in the Eclipse valve.
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Last edited by Solar on Tue May 12, 2009 8:17 pm, edited 1 time in total.
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Unread postAuthor: Ragnarok » Tue May 12, 2009 7:56 pm

Solar wrote:The interest in my launcher also stems from the FN303 fatality since these rounds are too big to penetrate an eye socket or to fit between ribs.

Suffice to say, I wouldn't want to catch one in the face or ribcage. There's the potential for broken bones at least.
But I suppose broken bones would prove a very convincing argument to cease whatever activity it was that was getting you shot.

I also suspect that they're interested at least because of the lower costs of ammunition. I know that FN303 ammunition isn't particularly cheap.

Anyway, with regards the video, I would expect that kind of order of energy involved in a impact at 50 yards, based on likely drag coefficients of such a projectile and the velocities that would be needed to get such a projectile to 250 yards like you say.
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Unread postAuthor: Hotwired » Tue May 12, 2009 8:02 pm

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Unread postAuthor: Solar » Tue May 12, 2009 8:22 pm

Thanks. I fixed the link in my post now as well. There is not pressure in the chamber left over per se. There is only the pressure that was used in the line to initiate the firing which gets vented out the stem of the trigger valve on the Eclipse. Similar to the "wasted" air that is hanging out behind a diaphragm valve, waiting to be exhausted. The safety of this valve stems (no pun intended) from the way that exhaust valves can fire if you lose pressure in the main chamber and the pressure on the other side doesn't bleed out proportionately.
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Unread postAuthor: Hotwired » Tue May 12, 2009 9:03 pm

I think you mean fire if the pilot side leaks and the chamber doesn't bleed proportionally.

The pilot actually has to drop quite a bit below chamber pressure if the chamber doesn't bleed back due to the differences each side sees in piston area. But still it's true enough.

I'm fiddling with sketches of a "new" (insofar as anything is new here) action which shouldn't require a gas pilot.

Most useful of the benefits is that it won't need the trigger valve to deal with massive pressure.
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