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Advice on a ""Proper" Cannon

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Advice on a ""Proper" Cannon

Unread postAuthor: Spuddy_McGee » Sat Dec 29, 2007 3:01 am

Hi,

So i'm about to construct my second cannon (first one not very effictient) and i have:

1meter x 50mm Barrel (can get 2meters if you think more efficient)
1meter x 90mm Combustion Chamber
90mm - 50mm Reducer
90mm Threaded Adapter (think thats what its called lol) + Screw on Lid
proper primer + glue
Need to purchase one of those pizeo bbq ignitors

I was just wondering if i should make the combustion chamber length about 50-55cm because i read something about a C:B ratio..

Also needed to know the correct way to rig up the bbg igniter with screws and wiring (last cannon involved shoving an actual bbg lighter in a hole in the back).

Thanks, (Im Aussie if you havent realised from the units) :lol:
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Unread postAuthor: rna_duelers » Sat Dec 29, 2007 5:28 am

C:B (Chamber:Barrel) ratios are very important in a combustion for performance,so to get that figured out.The C:B is in volumes,so if you have a chamber with 1000cc and a barrel of 1000cc it has a C:B of 1:1.The optimal ratio for a "advanced" combustion is around .8:1.But with a spray 'n pray type combustion a good ratio is around 1.5:1 or there abouts or so the word is that goes around although there isn't anything to back it up.

The Electric BAG sparker is fine,just wire it up nice and keep it dry.

the 90mm x 5500mm chamber sounds fine and a 50mm barrel is a good start,good for limes,potatoes and small onions.The pipe is all DWV I suppose?If so always aim those caps away from some one,they can pop off and they hurt like hell when they hit you.

Spudding fun,If you didn't guess I'm Aussie to mate :wink: .
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Unread postAuthor: Spuddy_McGee » Sat Dec 29, 2007 7:14 am

Thanks for all the great info,

I got all the pipe from bunnings (Australian Hardware Superstore) and it says UPVC and the primer and glue i got is 'the right one' so the worker says (neither have caused an issue on my last cannon).

Is intsalling a fan that important with a basic combustion or does it just increase the chance that your accelerant is going to ignite?
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Unread postAuthor: Hubb » Sat Dec 29, 2007 7:20 am

Spuddy_McGee wrote:...Is intsalling a fan that important with a basic combustion or does it just increase the chance that your accelerant is going to ignite?


The fan mixes the fuel and air to cause better ignition. If you've never used on in a combustion, it is well worth the investment.
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Unread postAuthor: bluerussetboy » Sat Dec 29, 2007 10:38 am

what i have found is, you can still get good results with accurate and consistent fuel/air mixes without a fan. not everyone has the resources to provide consistent fueling. a fan will help mix your fuel and air, but what i believe is just as important is it will help expel spent fuel and bring in fresh air between shots.

use a fan
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Unread postAuthor: Spuddy_McGee » Sat Dec 29, 2007 7:13 pm

Thanks for all the help,

Now i just need to look up how to install a fan and im set :lol:

Happy Spudding !
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Unread postAuthor: rna_duelers » Sat Dec 29, 2007 8:12 pm

www.burntlatke.com is the best combustion info website in the world I think,they have everything you need to know and more about combustion.

As for a fan,go to a computer store and ask for an old one that still works say its for a science project or something and you could get it for free,and to power it use 1 9Volt batterie and your doing fine.Oh and one very important thing!Mount the fan behind your Ignition source/spark gap,as you don't want the remains of a fan coming out of your barrel.
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Unread postAuthor: Spuddy_McGee » Sun Dec 30, 2007 5:29 am

Thanks so much RNA,

The site is great and has answered all my other questions =)
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Unread postAuthor: TwitchTheAussie » Sun Dec 30, 2007 7:25 am

No worries mate. You dont even need a soldering iron if ya handy with duct tape :lol: . And trust me, clean out the threads on the caps and make sure the fans properly secured.
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Unread postAuthor: Spuddy_McGee » Sun Dec 30, 2007 6:26 pm

what do you mean by cleaning out the threads on the cap?
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Unread postAuthor: sjog » Sun Dec 30, 2007 7:49 pm

file off casting ridges and bumps, lumps.
imperfections make it hard to screw in/out
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Unread postAuthor: Spuddy_McGee » Sun Dec 30, 2007 8:16 pm

ahh tyvm,

I've decided im going to use a chamber short for my ignition as well as installing a fan that was earlier suggested.

Should i buy http://www.bcarms.com/product_info.php? ... cee3a7c353 ?

i can get a fan easily enough but setting up a controller seems difficult...
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Unread postAuthor: TurboSuper » Sun Dec 30, 2007 8:43 pm

Call me cheap, but I don't think a full out controller circuit is necessary. Just a 9V and a switch should do the trick.
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Unread postAuthor: mark.f » Sun Dec 30, 2007 9:02 pm

Yes, two 9 volts, or just one 9 volt battery, will work fine, when wired in series with a switch before the fan.

And:

rna_duelers wrote:Oh and one very important thing!Mount the fan behind your Ignition source/spark gap,as you don't want the remains of a fan coming out of your barrel.


You can have the electrodes before the fan. Propagation of the flame front is independent of pressure rise through the chamber. Unless your fan is completely sealing the chamber after the sparks, nothing bad will happen.
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Unread postAuthor: Spuddy_McGee » Sun Dec 30, 2007 11:09 pm

With regards to setting up the fan i have:

-Soldering Iron (with the solderable metal stuff)
-80mm fan
-Plenty of wire
-Tons of screws + drill
-9v batteries
-Alligator clips
-"Black rubber with 2 metal circles for the battery" (lol)
-Scrap metal to hold it in place

All i need now is a switch which i can get a dick smith or tandy (Aussie electronics store); I think thats all i need.

My real issue is how should i go about setting it up so it looks neat and tidy? Could someone please provide a link to a basic setup or a diagram because i couldnt find one :?
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