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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 23, 2011 10:38 am

pneumaticcannons,

I don't make a living at it, but a fair amount of money has come my way from the pictures I take. It all goes to charity.

mark.f,

The trigger in this case is a CameraAxe/projectile sensor. The sensor measures the velocity and sets off the flash at a pre-set distance. It is useful when the projectile velocity varies.

By the way, congratulations on asking the right question. You would not believe how many people ask me what camera I am using to get these pictures. It's the flash/trigger that's key.

al-xg,

The arduino is a neat thing.

Most of my pictures, though, are taken with an analog home-brew set-up using chips (LM555) designed in the 60's. It doesn't measure velocity, though, so it is not as convenient to use as the CameraAxe.

The Axe, though, is very prone to upset by random noise from the flash etc. The LM555 circuit would work through a nuclear explosion.

Cheers.
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Unread postAuthor: Daltonultra » Fri Dec 23, 2011 6:42 pm

I knew I'd seen your work before! I have a picture on my HD of a grinning painted pumpkin just starting to come apart... It's one of my favorite high-speed photos, along with THIS ONE.

I would love to see what my favorite ammo looks like mid-splatter. Seeing a tin can full of pickled beets like that would be awesome... Got room for an eleven-foot cannon in your studio?
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Unread postAuthor: cometboy » Fri Dec 23, 2011 6:45 pm

Daltonultra,

I wish I had a larger garage.

Eleven foot would require breaking down a wall, though.

What is your favorite ammo?

Cheers.
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Unread postAuthor: Daltonultra » Fri Dec 23, 2011 7:15 pm

Canned food! My barrel is almost a perfect fit for no.2 cans. Think Spaghettios, soup, canned veggies, etc. Canned pickled beets are my favorite, because I absolutely LOATHE the taste and they give an incredible splash of color.

http://www.youtube.com/watch?v=hS5EOZVjMB0

On second thought, it really is more of "outside" ammo... :shock:
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Unread postAuthor: ramses » Fri Dec 23, 2011 8:36 pm

Nice pictures!

At first, I though you were her.
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Unread postAuthor: cometboy » Fri Dec 23, 2011 9:31 pm

ramses,

Jasper (she) got me started. When I saw that it was possible to build a fast flash, I built one.

Cheers.
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Unread postAuthor: Gun Freak » Fri Dec 23, 2011 9:48 pm

Mind blown. Incredible photography.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 15, 2012 3:27 pm

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3/4" Valve

Unread postAuthor: cometboy » Thu Dec 20, 2012 12:34 pm

It has been a long time since I posted. I am sorry if this makes me a bad SpudFiles contributor, but as I have mentioned before my primary interest is taking high speed photographs.

I have built up a second copper air cannon that I want to use for shooting small (~11mm) steel bearings.

The marbles work fine, but I want a smaller projectile that will have better penetration.

I am using the small silver 3/4" valve that was recommended to me and it does work. However it triggers really easily, sometime just when I disconnect the air hose from my schrader fill valve.

It this valve really that sensitive?

At this point I consider it to be a safety hazard since twice the cannon has fired without me pulling my trigger.

Cheers.
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Re: 3/4" Valve

Unread postAuthor: jackssmirkingrevenge » Thu Dec 20, 2012 12:51 pm

cometboy wrote:It has been a long time since I posted. I am sorry if this makes me a bad SpudFiles contributor, but as I have mentioned before my primary interest is taking high speed photographs.


No worries, we're delighted to have you here :)

It this valve really that sensitive?

At this point I consider it to be a safety hazard since twice the cannon has fired without me pulling my trigger.


Yes, it doesn't take much of a pressure imbalance to fire an exhaust valve.

An easy solution would be to fit a ball valve between the schrader and the launcher, which you would close before disconnecting the schrader.

Removing the schrader's core would allow you to use the ball valve itself as a trigger.
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Unread postAuthor: cometboy » Thu Dec 20, 2012 1:10 pm

Jack,

Just knowing that the valve is supposed to be sensitive is a great step towards a solution.

Thank you.

Off topic, but I bough ta refrigerator compressor that has none of the starting parts. I know it needs a PTC start relay and a run cap, but other than that.....

Any resources?

I am getting 540fps at 110psi and want to get a little more energy.

I would feel OK about going to 300psi, thus the compressor.

Oh and by the way I will "pay" with photographs :-)

Cheers.
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Unread postAuthor: jackssmirkingrevenge » Fri Dec 21, 2012 1:30 am

cometboy wrote:Off topic, but I bough ta refrigerator compressor that has none of the starting parts. I know it needs a PTC start relay and a run cap, but other than that...


That should be all you need: http://www.spudfiles.com/forums/fridge- ... 23869.html

Some other relevant threads, plenty of ideas here:

http://www.spudfiles.com/forums/i-has-f ... 20479.html

Here's a very well put together two stage setup:

http://www.spudfiles.com/forums/two-sta ... rt,15.html

Note that for 300 psi, you might want to consider a paintball type fill connector and hose:

http://www.ebay.com/itm/Heavy-Duty-THIC ... 35c2b2a56d

The above includes the male connector you would attach to the launcher, the line itself, and a slide valve on the line that allows you to purge it to disconnect. Basically you would need a 1/8" NPT female fitting on your launcher to connect the nipple, and a similar fitting on the fridge compressor outlet pipe to hook up the other end of the line.

While you're at it I would also pick up a mini 600 psi pressure gauge:

http://www.ebay.com/itm/New-600-1500-30 ... 416a9d0117

An automatic cut-off switch might also be a good idea for safety:

http://www.ebay.com/itm/UNITED-ELECTRIC ... 2322eae8f5
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Unread postAuthor: cometboy » Fri Dec 21, 2012 9:37 am

Jack,

You know your stuff for sure.

When I searched I didn't find much at all.

I will read these and figure out what to do. And when I get some "damage" pictures I promise to post them.

Cheers.
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Unread postAuthor: jackssmirkingrevenge » Fri Dec 21, 2012 10:25 am

Happy to help, it's quite simple really especially as you have some background now in spudguns as well as electronics. Just remember to be safe, 300 psi is nothing to joke with and without either careful manual control or an automatic cut-off, a typical fridge compressor will happily chug away to 600 psi and beyond.
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Unread postAuthor: Technician1002 » Fri Dec 21, 2012 11:09 am

If you have more than one flash, a digital divider chain can be made to fire a series of flashes in rapid order to capture the incoming projectile, then the resulting impact. Proper lenses can group the lighting to light the in flight projectile without exposing the impact zone several times. I have some plans to play with this using disposable camera flash units with the flash caps swapped out for much smaller values for shorter duration and lower intensity for zone lighting. With the set up, I could do up to 9 shots 0.1 to 1ms apart.
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