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Fixing my first spud gun

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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Unread postAuthor: Technician1002 » Sun Jun 27, 2010 6:11 pm

With the length of the chamber, some sort of mixing device is recommended. A plastic whiffle ball works well. add fuel, cap, and shake well.
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Unread postAuthor: Wayfast73 » Sun Jun 27, 2010 6:19 pm

I tried a 3 second spray of aquanet, I'm still not getting the distence I should be. The potatoes are tight I have the barrel knife edge. I'm going to see if I have a ecu fan laying around and try that.
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Unread postAuthor: spudtyrrant » Sun Jun 27, 2010 6:36 pm

Wayfast73 wrote:I tried a 3 second spray of aquanet, I'm still not getting the distence I should be. The potatoes are tight I have the barrel knife edge. I'm going to see if I have a ecu fan laying around and try that.
i would seriously think about trying a different fuel, ether(starting fluid) works really well, about 1 second of it should do. another problem you may be having is the huge length of your chamber, i had a combustion a while back with a chamber about 27"s long, it was weak with a single spark piezo ignition but when i upgraded to a stun gun and spark strip the power jumped significantly, if you can't get a more powerful ignition i suggest trying to get 2 sparks out of your piezo( 1 at the front of the chamber one at the back.
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Unread postAuthor: Wayfast73 » Mon Jun 28, 2010 3:22 am

Ill give that a try, using the 3 seconds of spray did make a difference. I saw some off laying around I know it releases bad chemicals but I tried a few shots of that and it did make a difference. Im going to pick up some starting fluid and a fan tomorrow and see how it goes. I was almost thinking about getting a 2" coupler and making the barrel a foot or so longer.
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Unread postAuthor: SpudBlaster15 » Mon Jun 28, 2010 12:29 pm

spudtyrrant wrote:another problem you may be having is the huge length of your chamber


Spudtyrrant brings up a good point. With a 24" long chamber and a single ignition point, combustion will take a fairly long time to complete, probably upwards of 30ms. Even with an inner muzzle bevel, the static friction of a spud slug is only about 5-10PSI. This means it will begin to move very early in the combustion process, and will probably be long gone before any significant amount of pressure has built in the chamber.

Multiple ignition points is definitely something to look into in this situation.
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Unread postAuthor: jrrdw » Mon Jun 28, 2010 3:04 pm

SpudBlaster15 wrote:
spudtyrrant wrote:another problem you may be having is the huge length of your chamber


Spudtyrrant brings up a good point. With a 24" long chamber and a single ignition point, combustion will take a fairly long time to complete, probably upwards of 30ms. Even with an inner muzzle bevel, the static friction of a spud slug is only about 5-10PSI. This means it will begin to move very early in the combustion process, and will probably be long gone before any significant amount of pressure has built in the chamber.

Multiple ignition points is definitely something to look into in this situation.


Or cut the chamber in half add a new plug and be done with it...
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