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Problems with mini

Discuss miniature cannons built from things such as pill bottles and pen caps.
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Problems with mini

Unread postAuthor: Rogue » Mon Nov 05, 2007 11:21 am

Ok I just attempted to make a mini combustion with the pill bottle and pen tube method. Except my piezo thingy does not click anymore. :(

But when i did get a spark in between the screws it would not light. So far i have used Axe and Bod. How much fuel do i put in there? Like a .5 second squirt or like a 1 second 1/2 half squirt?



Ahh help please
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Unread postAuthor: psycix » Mon Nov 05, 2007 11:28 am

The big rule of thumb on combustion fuel problems:
You got too much fuel
The big rule of thumb on mini combustions:
You always have too much fuel!

Put in the smalles spray you can, wave it forth and back a few times and then close it.
Experiment with the amount of times waving it.


OR use a syringe to measure out fuel.
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Unread postAuthor: Rogue » Mon Nov 05, 2007 11:31 am

ok thanks ill try that
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Unread postAuthor: CpTn_lAw » Mon Nov 05, 2007 12:07 pm

4% of gaz is very small....you really need to shake it back and forth...
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Unread postAuthor: Rogue » Mon Nov 05, 2007 12:46 pm

now i switched over to a little butane thing from a lighter. how long should i depress that thing for(gas). then how many times should i wave it???
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Unread postAuthor: CpTn_lAw » Mon Nov 05, 2007 1:00 pm

that depends...i suggest you try to inject 1/2 second of gas, then a little more if it isn't enough...try by increment of 1/4 second.
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Unread postAuthor: Rogue » Mon Nov 05, 2007 1:05 pm

when i move my screws back more i get a larger purplish spark. keep it like that or should i move them so they are very close together for a small bright blue spark?
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Unread postAuthor: Tom » Mon Nov 05, 2007 1:11 pm

You can also use a long nosed lighter, take out the nozzle, fuel hose and the gas tank(including valev). Glue the nozzle in the barrel as close to the spark-gap :!: , connect the rubbe hose from the long-nosed lichter to the lichter itself and the nozzle that is glued in your combustion chamber :!: . This wil have a result that you can put the feul in more accurate.
GR.Tom
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Unread postAuthor: Rogue » Mon Nov 05, 2007 1:15 pm

i am going to move to a glue stic one. ty tom
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Unread postAuthor: Rogue » Mon Nov 05, 2007 1:53 pm

GRRRR... i made another one out of a glue stic and i got it to work the first 2 times, one bod one butane.



should i let the chamber vent??
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Unread postAuthor: Rogue » Mon Nov 05, 2007 3:12 pm

UPDATE!


got it working. needed more fuel.


thanks guys


roguE
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Unread postAuthor: f.c » Mon Nov 05, 2007 4:02 pm

try using metholyted spirits. just one drop should be ample for a decent and reliable shot.
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can i be a sasquatch ?
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Unread postAuthor: jimmy101 » Tue Nov 06, 2007 10:49 am

You can convert a standard disposable butane lighter to a more accurate metering system like this.
Image

Even without a syringe, it'll work better than an un-mod'd lighter since you can get the small piece of tubing well up into the chamber.

One challenge with a mini is getting the fuel to mix well. Kind of hard to put a fan in a chamber that small. A couple of BBs can be added and then the chamber shaken to try to help mixing.

Another challenge with a mini is getting anywhere near a reasonable CB ratio. For 1/4" ID copper tubing as the barrel, and using a typical pill bottle that is what maybe 1"x2", you have a chamber volume of ~1.5 in<sup>3</sup>. For a 1:1 CB the barrel would have to be 30 inches long. A 6" barrel gives a CB of 5. The BIC pen body has an even smaller ID than 1/4" pipe so a BIC barrel would need to be even longer. A grossly too large chamber (CB too big) will significantly drop the performance of a gun.

The size of the spark doesn't make any difference, small spark, big spark, are all the same.
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