Experimenting with a REAL DIY vortex cannon!

Show us your pneumatic spud gun! Discuss pneumatic (compressed gas) powered potato guns and related accessories. Valve types, actuation, pipe, materials, fittings, compressors, safety, gas choices, and more.
highvoltagefeathers
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Thu Jan 10, 2013 5:42 pm

That looks like the design I was thinking about!

I shot the new coax cannon this morning, I'm fairly sure the spike is too large a constriction.

Going to remove it at first, then maybe try a smaller one.
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Brian the brain
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Thu Jan 10, 2013 6:19 pm

That design works for a coaxial valve with air entering from all sides, but falls short with air entering from only one side. You would want to modify it for single side air flow if used in a T.
That is actually completely true.

The T-valve I used this on had the pipe containing the piston sticking INTO the tee from the inside of a reducer.
That would mean it would act more like a coax at the first stages of opening..



I had completely forgot why I had done that apart from me liking compact designs.
At least...I had not taken that in account when I did the drawing.
So a very valid statement indeed.

The other valve I used it on was a modified solenoidvalve.
I had designed a completely new top for it so it could house a piston in stead of a diaphragm.
( Psycix eventually milled that for me)
Wich is also much more suited for this type of cone.

So..in a regular Tee valve you would need a "cone" that is shaped like the inside of an elbow...and something to keep it from rotating..ideally speaking
Gun Freak wrote:
Oh my friggin god stop being so awesome, that thing is pure kick ass. Most innovative and creative pneumatic that the files have ever come by!

Can't ask for a better compliment!!
PVC Arsenal 17
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Thu Jan 10, 2013 7:29 pm

I am curious if a section of straws prior to the cone would help collimate the flow so it will enter the cone more uniformly.
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Insomniac
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Thu Jan 10, 2013 8:11 pm

@PVC, I had the same idea... Like what's used in wind tunnels. It might be quite restrictive, however.
I wonder how much deeper the ocean would be without sponges.
Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before.

Add me on msn!!! insomniac-55@hotmail.com
whoa044
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Fri Jan 11, 2013 12:19 am

This is so untrue; you can definitely send a projectile off faster than the speed of sound of the gas you are using.

It really just depends on how much energy you put into the gas and how well you can use that energy.

If I made a burst disk cannon with the disk's rupture pressure around 10,000 psi, I'm sure I could easily send things flying over the speed of sound while using air.
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Fri Jan 11, 2013 12:29 am

It can be done (and has) but it's not that simple. Certain anomalies (mentioned on page 1) must occur first.

From Wikipedia - "The limiting factor on the speed of an airgun, firearm, or light-gas gun is the speed of sound in the working fluid—the air, burning gunpowder, or a light gas. This is essentially because the projectile is accelerated by the pressure difference between its ends, and such a pressure wave cannot propagate any faster than the speed of sound in the medium."

It's a fascinating concept.


Go to 5:07

Also:
http://www.physicsforums.com/showthread.php?t=386687


Sound is nothing but a compression wave. The speed of "sound" in a medium simply means the speed at which a compression wave (a "push") can travel through a given medium.
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matti
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Fri Jan 11, 2013 4:53 am

whoa044 wrote:This is so untrue; you can definitely send a projectile off faster than the speed of sound of the gas you are using.

It really just depends on how much energy you put into the gas and how well you can use that energy.

If I made a burst disk cannon with the disk's rupture pressure around 10,000 psi, I'm sure I could easily send things flying over the speed of sound while using air.
No. Well.. You can get it little over the SOS, but not much higher.. Its like you cant use airgun to shoot 1000m/s.. There is ways to do that but its done by using different gases and heat to get the SOS up.. Thats the only reason they have Light gas guns.
highvoltagefeathers
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Fri Jan 11, 2013 5:11 am

The speed of sound is a very relative thing, and varies greatly depending on the gas you are using, the heat and pressure of that gas, etc.

It holds that a projectile cannot be propelled faster than the speed of sound in the propellant gas.

The "weird physics" that accounts for an air-powered gun shooting faster than the atmospheric pressure, room- temperature speed of sound in the air around us, is that the speed of sound in compressed air is higher (by varying degrees depending on pressure) than at atmospheric.

"But" you say,

"Speed of sound is dependant /only/ on temperature."

For a theoretical, ideal gas, this is true.

Air is not an ideal gas. Its component molecules interact, and take up space.

Air at 10,000 PSI would deviate significantly in behavior from an ideal gas, due to the inherent increase in density. This would raise the speed of sound in this propellant gas.

This deviation, even at pressures as low as 1,000 PSI, is significant enough to account for the "mysterious" chrono readings so often debated on these forums.

If you used air at 10,000 PSI, I don't doubt that you could get a projectile to far exceed the speed of sound in air at standard conditions.

But it would not exceed the speed of sound in its propellant gas.
highvoltagefeathers
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Fri Jan 11, 2013 5:17 am

Especially in the case of a "spring-piston" pellet gun, and other such devices (such as a light-gas gun), you also need to account for the rapid heating (a factor which greatly impacts the speed of sound) due to compression of the propellant gas (air) which occurs during firing.
highvoltagefeathers
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Tue Jan 15, 2013 6:57 pm

So at first the coaxial design did not work.

I removed the "spike" at the end of the barrel-seal, and it improved.

I further refined the barrel-seal with gasket material, rather than a machined rubber stopper, and it began producing vortex rings just as well as the "T-Valve" cannon did.

However, I'm still looking for more.

I built a simple combustion chamber, and have been experimenting with Acetylene.

I AM FULLY AWARE OF THE DANGERS OF ACETYLENE. IF YOU PLAN ON LECTURING ME, SPARE YOUR KEYBOARD THE ABUSE.

The chamber is short and stubby, with central ignition, to reduce the possibility of detonation.

I am also using no cover, wrapping, burst disk, etc. to hold the gas in.

There are no obstructions to the chamber exit.

Here is a video. Some "tuning" the mix has further improved the aparent intensity of the vortex.

[youtube][/youtube]
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jackssmirkingrevenge
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Tue Jan 15, 2013 7:00 pm

highvoltagefeathers wrote:[youtube][/youtube]
hectmarr wrote:You have to make many weapons, because this field is long and short life
highvoltagefeathers
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Tue Jan 15, 2013 7:03 pm

Thanks, not sure why mine wouldn't work...
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MrCrowley
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Tue Jan 15, 2013 7:06 pm

It's the 's' in https:// that stops the link from working if I remember correctly.
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jackssmirkingrevenge
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Tue Jan 15, 2013 7:11 pm

yup as mrc said
hectmarr wrote:You have to make many weapons, because this field is long and short life
aegisknight
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Tue Mar 26, 2013 6:58 pm

Technician1002 wrote:
Image
That design works for a coaxial valve with air entering from all sides, but falls short with air entering from only one side. You would want to modify it for single side air flow if used in a T.
What if there was an input on both sides, with the valve releasing pressure both from the top and bottom simultaneously? That should equalize the pressure difference and act similarly to complete circular pressure
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