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Fus Ro Dah Fail

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: PVC Arsenal 17 » Mon Jan 09, 2012 2:16 pm

Without knowing anything at all about them, I decided to try making a toroidal vortex launcher.

I had no clue where to start or how to do it so I just dove right in and made a simple burst disc cannon with a cone for a barrel like this or this.

Needless to say it didn't work. Beyond a few feet it didn't even rustle a paper bag and when I dusted the cone with baby powder, it produced no noticeable rings.

Can anyone with more knowledge on the subject help me out? My best guess is that the cone (funnel) I used is not gradual enough.


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Unread postAuthor: jackssmirkingrevenge » Mon Jan 09, 2012 2:47 pm

maybe it needs to be a combustion to work like that, simply using a conical barrel?

how about a barrel made of two coaxial tubes, with the air travelling between them...
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Unread postAuthor: Alster370 » Mon Jan 09, 2012 2:56 pm

Id keep the design similar to the one they did on the big bang theory:
http://www.youtube.com/watch?v=IyAyd4WnvhU

The one in the video is a combustion, and I believe it works best when it is, due to how fast the pressure is built up.
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Last edited by Alster370 on Mon Jan 09, 2012 2:58 pm, edited 1 time in total.
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Unread postAuthor: Gippeto » Mon Jan 09, 2012 2:57 pm

Couple wags off the top of my head. :roll:

Would think an oriface plate (similar to a flat washer) would be required to initiate the vortex ring.

Would also think a constant taper might be important. Pulling an angle from somewhere dark, I'd try 11-12 degrees.
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Unread postAuthor: MRR » Mon Jan 09, 2012 5:41 pm

I agree with Gippeto. In all vortex cannon that I have seen so far there was a controlled "bottleneck". You can see it at the example of an airzooka.

Image

You could try to put a expansion chamber in front of the funnel.

Edit:
This video has been posted before but I thought this remix is hilarious... :D

[youtube]http://www.youtube.com/watch?v=Ip7QZPw04Ks[/youtube]

and another...
[youtube]http://www.youtube.com/watch?v=oBcGj4mpJ98&feature=endscreen&NR=1[/youtube]
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Unread postAuthor: PVC Arsenal 17 » Mon Jan 09, 2012 9:28 pm

I tried a washer restriction and it didn't change much.

I think I'll start building a combustion version like that guy's prototype in the video above. Any ideas for closing off a combustion chamber so propellant gasses don't escape before firing? (Because there is no projectile)

...Other than burst disks which are inconvenient for rapid firing.
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Unread postAuthor: Lockednloaded » Mon Jan 09, 2012 9:30 pm

Piston combustion? You could build a tee valve with a light spring holding the chamber sealed. Kinda overkill though if you ask me...
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Unread postAuthor: jackssmirkingrevenge » Tue Jan 10, 2012 12:54 am

Lockednloaded wrote:Piston combustion? You could build a tee valve with a light spring holding the chamber sealed. Kinda overkill though if you ask me...


Why not just jam a wad of toilet paper in the breech? It doesn't have to hold pressure anyway. Besides, as discussed in another thread, and as jimmy will tell you vehemently with the power of science behind him, in practice it would take ages for the gas to diffuse anyway, so it might not even be necessary.

Also, I've never played Skyrim but I have enough internets in me to know that your launcher probably used to work, but took an arrow to the knee.
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Unread postAuthor: pneumaticcannons » Tue Jan 10, 2012 5:40 am

Why not just jam a wad of toilet paper in the breech?

That would probably disrupt the toroid...
I think the piston idea would work nicely however and you could always attach a real barrel if you get bored of shooting air :wink:

But I don't think making it combustion will make much of a difference. As stated above, the cone probably needs to be a lot more gradual like the smoke ring shooters seen on Bang Goes the Theory and myth busters.
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Unread postAuthor: warhead052 » Tue Jan 10, 2012 11:26 am

Meh, just make it a hybrid if you go with a piston combustion. Same concept, but you just add air. Dunno if it would work though.
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Unread postAuthor: Insomniac » Wed Jan 11, 2012 5:00 am

I've built a few little vortex cannons before, and I think your problems are that the shape is incorrect on this scale, and you are using way too much air.

One of the most effective ones I made was a long postal tube (maybe 50cm long and 10cm in diameter), with a hole drilled in the cap at the end (about 5cm diameter).

A latex skin was stretched over the other end of the tube. Pulling it back and releasing would send a vortex ring quite rapidly across the room... It could be felt from a good 3 or 4 metres away in still air.

I don't think this would have worked if I had added a large chamber and valve where the latex diaphragm was. The setup I had provided a very rapid pulse of very little air, which formed the ring. I think if you are going to use a pneumatic setup, design it so that your valve dumps behind a captive piston with very little travel... Meaning each shot will move the piston a very short distance very rapidly, generating a sharp, controlled pressure wave in the tube.
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