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The baby hydra!

Built a miniature 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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The baby hydra!

Unread postAuthor: inonickname » Thu Feb 26, 2009 3:53 am

Following on from this mini I wanted more power, more accuracy, more aesthetics, the works.

The result was a mixture of aluminum, brass, stainless steel and epoxy.

Specs are as follows:

Chamber O.D.: 20mm
Chamber I.D.: 14mm
Chamber construction: Aluminum
Chamber port (barrel): 1/4" NPT brass. (female)
Chamber port (ignition): 1/4" NPT brass. (female)

Barrel bore: 5.5mm
Barrel O.D.: 6.5mm
Barrel construction: Stainless Steel
Barrel port: 1/4" NPT brass. (male)
Accommodates an adhesive burst disk. Eg. - Masking tape, electrical tape, duct tape.

Spark plug: Single gap, 4mm. Centred in chamber. Sealed with epoxy and silicon.

Ignition: Piezoelectric for portability, camera flash, stungun or flyback circuit.

Testings so far: The electrolysis unit is giving me troubles. I can't use a wall transformer due to my local parents against everything group, and it hasn't yet yielded me enough H2/O2 for ignition..So more will come as the hydrogen setup is completed!

It has been tested with these fuels: Butane, 95% propane 5% butane mix, misted acetone and misted turps. So far 95% propane 5% butane has shown the best power and noise. Other fuels have shown difficulty in metering.

The burst disk makes a psst-crack sound with no projectile, a psst-snapping sound loaded and a loud crack with no barrel.

Ammunition testing so far has mainly been wads or a few undersized bb's that came with some toy gun so there's no real damage pictures as of yet. I will be casting slugs (ala this), except using two pieces of thick plate cut from angle, and with multiple slugs per mould.

The barrel, brass fittings and chamber have been buffed and polished, even if it doesn't show in here. If It's possible, I may blue the barrel.


And onto the part you skipped down to, the photos!

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Rearwards shot next to the advanced mini.

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Barrel and chamber. There is a masking tape burst disk mounted on the barrel.

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The gun, disassembled.

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Disassembled gun with modified bic lighter (be wary of these, it's given me some fueling problems..any ideas why? seems to have ignition problems even when metered with a syringe). And a large piezo (courtesy of gas hot water system).

If you're interested, the C:B ratio is exactly 1.1:1. Pre spark plug, it was exactly 1.5:1, but the oversized spark plug wrecked this.

Future updates:
Split mold with multiple lead slugs.
Cannon mount
Shortened spark plug to bring the cannon back to a 1.5:1 ratio
Compact camera flash ignition
Complete electrolysis unit to run the cannon on pure 2H2/O2
Damage pictures/videos (after hydrogen fueling)
More research on fuel and burst disks.

I guess you all just looked at the pictures and barely skimmed the writing. I don't blame you, and I don't mind.

Any input at all is welcome. Tell me what you think.
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Unread postAuthor: CpTn_lAw » Thu Feb 26, 2009 5:11 am

this is a nice mini!!!! everything seems to be fine with it! Fuel mixtures are hard to get right with these, you have to be ver precise as the most little change affects the combustion by a great amount.
It's strange that you hear a noise before the cracking sound of the burst disc; you should only hear the click, and kaboom. How do you estimate the speed now? with 2H2/O2 ?
Great mini cannon, and btw, we usualy read everything when we come to ask questions !!
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Unread postAuthor: inonickname » Thu Feb 26, 2009 5:40 am

It hasn't been tested with hydrogen/oxygen yet unfortunately due to electrolysis problems. The fuel mixture wont be a problem after that due to hydrogen's large combustion window and the presence of oxygen.

I suspect that there was a leak in the spark plug, then the pressure sealed the plug and it fired. This has since been remedied with silicon then a plug of epoxy. Now it's an instant sound, no sound before.

Unfortunately, I have no access to a chrony but I'm looking into using sound over distance as a measure, I think it's been posted here before. I believe that with the longer, smoother barrel, more volatile gas, presence of oxygen will easily quadruple the performance of my last mini.

Stay tuned, I'll snap some damage shots with propane soon. (working on electrolysis at the moment)
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Unread postAuthor: psycix » Fri Feb 27, 2009 3:56 pm

Beautiful mini.
H2/O2 would certainly suit it.

Any more information (pics!) on the electrolysis machine? You should post it when its done.
What are you using as electrolyte? (Do NOT use salt. I'm not sure if you know or not, but this will yield Chlorine gas instead of Oxygen)
I usually use drain cleaner (NaOH).
What are your electrodes made of? Stainless steel bolts?

You can use any wall transformer safely, as transformers are a protection to short-circuiting. They simply cant give more amperes when shorted. You should just keep an eye on overheating the thing and you will be perfectly safe.
The electrolyte chemicals or the hydrogen produced are a far more serious safety issue then the wall transformer.
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Unread postAuthor: inonickname » Fri Feb 27, 2009 7:56 pm

psycix wrote:You can use any wall transformer safely, as transformers are a protection to short-circuiting.


Not how my parents feel, even though one of them used to have a job building circuit boards....

It will be battery powered, I'm trying to find some steel mesh. I think the bolts I used were coated so it didn't work well.

Thanks :P

Oh btw, I use Bi-carb of soda.
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Unread postAuthor: Insomniac » Fri Feb 27, 2009 8:22 pm

Be wary of using stainless steel in electrolysis. I've heard that the chromium erode off it and into the water. I haven't found much good info on just how risky this is though.
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Unread postAuthor: inonickname » Sat Feb 28, 2009 7:25 pm

Updates:

Firstly, the new electrolysis unit.

It's quite simple, a clothing detergent bottle that's been cleaned out thoroughly. Two steel nails (not stainless) are used as electrodes. An rc car charger is used to supply DC current. I use baking soda(bi-carb) and water as a fuel. Plug it in, and there are so many bubbles you can't even see the electrodes.

Now here's the problem. It produces some gas that doesn't burn. I collected it and tried it in the gun, no result... I even held a ciggarette lighter over the delivery tube, and the flow was quick enough to put it out! It didn't ignite/burn better or anything..gah..

Anyone know what's wrong?
-Steel (not stainless) electrodes
-DC current
-tap water and bi-carb/baking soda
-non-flammable gas.


New spark plug:

Simple enough, just a much shorter and cleaner spark plug. Occasionally arcs to the outside of chamber, not that it really matters.. It's the green/brass/copper part.

Split mould:

A split mould, inspired by gippeto. Works absolutely fine, ignore the unevenness.

I also mixed up ballistics gel (gelatin mixed to a certain recipe) to get some test firings done while on hydrogen.

Image

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No current.

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Current.


It would be great if anyone could help troubleshoot my problem with electrolysis..I can't figure out whats wrong with it. My main suspicion is the electrodes but I'm unsure.

Thanks guys :wink:
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Unread postAuthor: inonickname » Sun Mar 01, 2009 3:14 am

Well I've been looking through instructables and this one stood out.

It's a truly neat looking piece of equipment, but it also states not to use salt (of course) and not to use baking soda as it will produce carbon monoxide.

After discussing the issue, my parents completely lost it when I suggested caustic soda/drain cleaner..So thats out of the question.

Any other ideas?
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Unread postAuthor: psycix » Mon Mar 02, 2009 1:38 pm

Highly concentrated caustic soda isnt that bad or dangerous. Well, as long as you dont spill it ofcourse.
You could try a different electrolyte or/and you could try running it for longer.
Maybe there were impurities that had to be electrolyzed first, preventing hydrogen gas production.

For the electrodes you should try to use something made from stainless steel. Hardware stores sell stainless steel bolts and washers. (Great to enhance surface area!)
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