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Copper Marble Cannon

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: cometboy » Fri Dec 21, 2012 12:17 pm

Jack,

I plan to go slowly as I do not really know what I am doing. And I may never go to 300psi since my present 129psi/540fps has a fair amount of power. 1/2" plywood penetration is impressive to me.

Technician1002,

The lenses sound like a difficult part of your idea. Look up Cranz-Shardin camera to see an old idea for use in shadowgraph style high speed photography.

As far as the flashes, I have seen a number of attempts to use disposable flashes for high speed imagery. Never saw any results.

A basic problem is that xenon has a long duration of light emission once it is excited. The only way I know to reduce this is to confine the xenon in a narrow channel, which de-excites the xenon by collision with the walls.

The bottom line is that the easiest way to get a fast flash is by using a classic Edgerton air gap flash. And they are bulky units.

Good luck with your project.

Cheers.
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Unread postAuthor: Technician1002 » Fri Dec 21, 2012 1:34 pm

If you have access to theater lighting fixtures, Ellipsoidal fixtures make great flash lamp holders for this type of effect. I'm not sure the cool down period for disposable flash lamps. They are not large diameter so some experimentation will need to be done to measure flash duration. For air cannon speeds, it may have some blur, but may be acceptable. It will not be fast enough to get blur free images of high speed rifle rounds.

With flashlamps in close proximity of the projectile flight path and low energy flashes, fancy optical lensing is not required. Aim each reflector prior to the impact zone toward the source so it does not illuminate the target.
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Unread postAuthor: cometboy » Fri Dec 21, 2012 4:03 pm

I'll look into the reflectors.

You idea has merit. But as far as I understand it, you would get a bunch of shots of a projectile traveling through the air.

A great technical achievement, but I have doubts that it would be visually interesting.

The impact is when things really start happening.

A decent Photoshop user could give you a nearly perfect simulation of a marble/pellet/etc traveling through the air.

Heck, even I could do it :-)

Cheers.
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Unread postAuthor: Technician1002 » Fri Dec 21, 2012 6:50 pm

2 or 3 exposures prior to impact is for an optical chrono. Time base would be divided from a crystal oscillator. The launch trigger would release the counter. Marshmallow distortion would be another reason for pre impact photos.
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Unread postAuthor: cometboy » Fri Dec 21, 2012 6:54 pm

Technician,

I see where you are coming from.

As an optical chrono it might work.

I would be worried that flash jitter ie variations from flash to flash would be a big source of error. Especially compared to your quartz xtal time base.

I am most often coming from a "How do I make a good photo" direction.

Cheers.
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Unread postAuthor: Technician1002 » Fri Dec 21, 2012 10:56 pm

A CDI trigger has very little jitter in ignition time. The initial gas ionization is very quick and the resulting avalanche is immediate if the flashtube voltage is high and there is no long leads to prevent rapid rise in current. Low iron content trigger coils with fast rise times have less jitter than cheaper ones wound on a laminated iron core. Those have slower rise times and thus more jitter due to variations in trigger time on the slower rise of trigger voltage. Use fast SCR's in your trigger circuit for low levels of jitter.
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Unread postAuthor: cometboy » Wed Dec 26, 2012 8:50 pm

To Whomever,

I said that I would post a few images once I got my new cannon up and running.

It's at low pressure, I am still working to get my refrigerator compressor running. I bought a bare compressor, no starting parts, so.....

I also had a problem with the unit triggering too easily. This was fixed by adding a check valve after the schrader fill valve. This was a good change as the unit was disconcertingly sensitive to slight pressure variations.

The steel ball doing the damage is ~11mm in diameter, 4.5 grams moving at about 550fps @110psi.

<a href="http://www.flickr.com/photos/8763834@N02/8312966138/" title="Cracked Cock by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8080/8312966138_3966d12b71_m.jpg" width="192" height="240" alt="Cracked Cock"></a>

<a href="http://www.flickr.com/photos/8763834@N02/8312712102/" title="Crayon Collapse by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8217/8312712102_c81b64b01a_m.jpg" width="236" height="240" alt="Crayon Collapse"></a>

<a href="http://www.flickr.com/photos/8763834@N02/8311646073/" title="Goodbye Santa by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8362/8311646073_70339dbfb6_m.jpg" width="165" height="240" alt="Goodbye Santa"></a>

Two great things about using steel bearings.

First I can re-use them.

Second, no more plastic tubing down the barrel to load glass marbles. I use a little NIB magnet to pull the bearing down the copper barrel and keep it in firing position using another small magnet. I am sure that this is not a unique idea, but it sure is fun to do.

Faster, too.

Thanks very much for the help.

Cheers.
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Unread postAuthor: PaperNinja » Wed Dec 26, 2012 9:51 pm

I love the crayon picture!
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Unread postAuthor: POLAND_SPUD » Wed Dec 26, 2012 10:36 pm

awesome pictures :)
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Unread postAuthor: jackssmirkingrevenge » Thu Dec 27, 2012 1:26 am

Fantastic stuff, kudos! Expect a lot more violence at 300 psi ;)
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Unread postAuthor: cometboy » Fri Dec 28, 2012 4:00 pm

All,

A few more images.

I should be getting parts for my compressor in a few weeks so I can work on the higher pressure. I don't think I'll be going to 300psi but we shall see.

<a href="http://www.flickr.com/photos/8763834@N02/8316443888/" title="Non-Mayan Chocolate Apocalypse by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8218/8316443888_2513a2c24a.jpg" width="500" height="300" alt="Non-Mayan Chocolate Apocalypse"></a>

<a href="http://www.flickr.com/photos/8763834@N02/8317971843/" title="Apples Are Easy by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8223/8317971843_676b1cee75.jpg" width="500" height="280" alt="Apples Are Easy"></a>

<a href="http://www.flickr.com/photos/8763834@N02/8319579502/" title="No Name Beer by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8214/8319579502_b32bee07bf.jpg" width="239" height="500" alt="No Name Beer"></a>
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Unread postAuthor: jackssmirkingrevenge » Sat Dec 29, 2012 12:57 am

Amazing work as always.

I think higher pressures will be a revelation. Remember that pressure is directly related to muzzle energy, effectively by going to say 220 psi you would roughly double your current energy and this will translate into more rapid going-away-from-the-place-they-were-before for the components of your targets and therefore more dramatic pictures.

Also, have you considered filming the projectile leaving the muzzle? That should make for an impressive shot. Also, why not invert the theme and shoot frangible objects at hard surfaces?
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Unread postAuthor: cometboy » Sat Dec 29, 2012 9:48 am

jack,

I'd love to do film but the cameras are really expensive. About 30K$ for reasonable quality. Too much for this photographer.

My first air cannon was a 70psi PVC unit. I shot limes, ping-pong balls, Christmas bulbs filled with gelatin etc.

http://www.flickr.com/photos/8763834@N0 ... 669945216/

I got lots of fun pictures.

Cheers.
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Unread postAuthor: cometboy » Mon Dec 31, 2012 5:20 pm

So I tried hooking up the refrigerator compressor today.

It seems to work.

It doesn't like back pressure, refuses to start.

I ran it up to 200psi and shot a few bearings. Much faster, I don't have velocity numbers but it goes through ~100% more plywood, about 1".

I am not going to take any pictures with it until I get it all "packaged" and safe.

Here is a banana at 110psi. I like it.

<a href="http://www.flickr.com/photos/8763834@N02/8330414557/" title="How to Peel a Banana by alan_sailer, on Flickr"><img src="http://farm9.staticflickr.com/8360/8330414557_97daf40102.jpg" width="500" height="319" alt="How to Peel a Banana"></a>

A few question, please.

First what revenge is jack smirking about?

And I am curious about the photograph for Mr Crowley. It's just a strange little picture. Who, what, were is it from?

If these are dumb questions, feel free to ignore them.

Just curious.

Cheers.
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Unread postAuthor: cometboy » Mon Dec 31, 2012 8:03 pm

I realized I can post the animation also.

<a href="http://picasion.com/" rel="nofollow"><img src="http://i.picasion.com/pic63/b8e071e4c2ef7d0ce86f4c6c7e2dc2de.gif" width="300" height="191" alt="make gif"></a>

I promise I won't spam the forums too badly.

Cheers.
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