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Problem with Spark Plug

Post questions and info about hybrid (compressed gas with fuel) powered cannons here. This includes discussion about fuels, ratios, ignition systems, build types, safety, and anything else relevant.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 01, 2012 2:05 am

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Unread postAuthor: MrCrowley » Thu Nov 01, 2012 2:22 am

Got a 44 gallon drum you can send me, then? :D dammit.
Bit far away for me though.

Actually, it would be pretty fun making it and getting it to work well.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 01, 2012 2:33 am

Actually, I do! And we sell them for scrap for less than a euro each.

Sending an empty one across the world would be pretty silly though.

http://www.trademe.co.nz/sports/equestr ... 997099.htm ?

Which silly named part of the country are you in?

If you want to be really hardcore: http://www.plastic.co.nz/plastic-products/7993.html

:D :D :D
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Unread postAuthor: MrCrowley » Thu Nov 01, 2012 2:45 am

I'm in Auckland as well but parts of Franklin are 80km away.

Would a 44 gallon drum even be large enough you think? Do the ones with tyre baffles work that well? I probably know some people that could get me the right sized tyres without too much hassle. Then again, transporting this thing would be a b|tch.

Some what related:
[youtube]http://www.youtube.com/watch?v=zbtCDyASvt0[/youtube]
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 01, 2012 3:45 am

Would a 44 gallon drum even be large enough you think? Do the ones with tyre baffles work that well? I probably know some people that could get me the right sized tyres without too much hassle. Then again, transporting this thing would be a b|tch.


If I remember well, you have around 1.5 litre chamber size.

Sorry if this sounds patronising.

Let's go crazy and go for 15x, and say that for every mix number, you're getting 150 psi. This gives us 2250 psi in the chamber. Let's say we release that pressure to a closed 44 gallon drum.

Completely ignoring the fact that the hot gasses will lose pressure as they cool, let's agree with Boyle that pV is constant. The drum has around 200 litre capacity, so if we had to allow the chamber to expand into the drum, the resultant pressure is just 17 psi.

Now, a drum like this is not a rated pressure vessel and is probably not safe beyond 5 psi, but remember that if made as a suppressor it will not be a closed tube, so that is not an issue. Also, I have grossly overestimated the amount of pressure generated in your chamber, I doubt you're running at more than 800-1000 psi in practice.

In short, it's more than enough for your purposes :) Even if you leave it completely bereft of baffles and packing material (maybe pour a bottle of water into it so it can be fired "wet")

Some what related


This one's better, and by better I mean *much more insane*

[youtube]http://www.youtube.com/watch?v=Bczn_1S8SYo[/youtube]

:D
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Unread postAuthor: MrCrowley » Thu Nov 01, 2012 4:07 am

I guess it's just hard to visualise how well it could work.

If I can get a drum fairly easily, and a bunch of tyres that fit, I might give this a go over summer. I don't think it will make a radical difference to how often I get to shoot but I'd love to give it a go for the sake of it.
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Unread postAuthor: Zeus » Thu Nov 01, 2012 4:32 am

Testing like you have been will show nothing whatsoever! Get out your multimeter, set it to the highest resistance setting, (should be 10 megaohms), put one lead on the centre terminal, and the other on the return(wherever you put the other lead from your ignition).

Simple, it should be completely open circuit, no reading whatsoever. If it isn't, replace the plug.
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/sarcasm, /hyperbole
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Unread postAuthor: MrCrowley » Thu Nov 01, 2012 4:53 am

Ah yup, I had tried that when messing around and I got no reading on any of my plugs.
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 01, 2012 5:25 am

I guess it's just hard to visualise how well it could work.

If I can get a drum fairly easily, and a bunch of tyres that fit, I might give this a go over summer. I don't think it will make a radical difference to how often I get to shoot but I'd love to give it a go for the sake of it.


Its fairly simple. The gas in the chamber wants to reach atmospheric pressure, and in order to do so it needs to grow in volume. If you keep it "restrained" while it does that, voila, much less sound.

If you're firing supersonic there's still the sonic crack to attract attention of course. I would recommend a perforated barrel and the drum welded to it.
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Unread postAuthor: jrrdw » Thu Nov 01, 2012 9:27 am

The 2 liter plastic soda bottle seems to work well, as long as you can keep it on there L0L :D
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 01, 2012 9:54 am

jrrdw wrote:The 2 liter plastic soda bottle seems to work well, as long as you can keep it on there L0L :D


On a 6mm mini hybrid perhaps, but not on MrC's beast!

Speaking of beasts, have you got a cat?

Image
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Unread postAuthor: MrCrowley » Thu Nov 01, 2012 2:20 pm

jackssmirkingrevenge wrote:If you're firing supersonic there's still the sonic crack to attract attention of course. I would recommend a perforated barrel and the drum welded to it.
Haha well welding it to a barrel is out of the question. This is something I would try a few times and then get rid of or leave in the corner. It would be so heavy and unwieldy. It also only solves the problem of noise, the shooting location still has a small road and field behind it where, more often than not, the presence of people prevent me from setting up. I still have the problem of not being able to shoot targets safely either. Half my videos on YouTube of this cannon are either dry fires or shooting a projectile at nothing :D

So as you can see, it's still not something I would invest much time or money in as it doesn't solve many of the problems that affect my shooting frequency.

It'd still look cool though :P
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Unread postAuthor: jackssmirkingrevenge » Thu Nov 01, 2012 2:23 pm

MrCrowley wrote:It would be so heavy and unwieldy.


Well, if you could get your hands on another barrel that's threaded on the muzzle end...
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