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Boom! The classic potato gun harnesses the combustion of flammable vapor. Show us your combustion spud gun and discuss fuels, ratios, safety, ignition systems, tools, and more.
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jackssmirkingrevenge
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Tue May 01, 2012 2:08 am

battlelava wrote:I was using carb cleaner, because i got no luck with propane.
... because you didn'tuse a syringe ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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battlelava
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Tue May 01, 2012 6:18 am

jackssmirkingrevenge wrote:
battlelava wrote:I was using carb cleaner, because i got no luck with propane.
... because you didn'tuse a syringe ;)
I know I have to find a place nearby to pick one up. Ill get a fan while I'm at it
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Technician1002
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Tue May 01, 2012 6:31 am

Canned air is not air.
Heres how i prepared to shoot. I used the compressed air can to start the mixing processes, and then i used a ghetto cardboard fan.
Read the ingredients. For air, you need something with Oxygen in it. The dusters will displace Oxygen and reduce power or completely prevent ignition.

Starting fluid is a better fuel than carb cleaner.
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battlelava
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Tue May 01, 2012 8:26 am

The duster said combustible on it so I figured it would make a good mixer because I don't have a fan. Ill check CVS for a syringe and ill start using propane and I'll try it out again. I guess I could use that cup reversed with bbs




I made a new projectile, it was 3 cardboard cutouts with a middle block to give it length, wrapped in paper for better aerodynamics. Only problem was when i fired it it just turned instead of launching. Does it need to be a certain length.
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battlelava
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Thu May 03, 2012 8:39 am

So after looking at some hdgt results with proper propane fueling, I'm starting to question how effective this would be. I'm not sure how much deviation it would has because it doesn't account for the bb's separating from the casing, But I've only got results of like 200 ft, and so far i've only got results of around 20 ft (avg)

Edit: was suppose to be an edit on the other post :angryfire:
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Technician1002
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Thu May 03, 2012 10:12 am

If it is combustible, it is a fuel and can result in a rich mix. How combustible is it? Is it butane? The label may indicate what it is.
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battlelava
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Thu May 03, 2012 10:24 am

Technician1002 wrote:If it is combustible, it is a fuel and can result in a rich mix. How combustible is it? Is it butane? The label may indicate what it is.
Does not say, I was under the assumption that it was compressed air and air getting more dense of oxygen the cooler it gets. Also I got one of the best launches while i used it.


I just tried it again with a snug fitting piece of cardboard, hit ignitor, ignited but nothing happened. Guess i'm back to the drawing board?
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battlelava
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Sun May 06, 2012 4:45 pm

Would this type of syringe work. It was for 0.9% sodium chloride IV flush. Goes up to 10ml
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jackssmirkingrevenge
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Sun May 06, 2012 4:47 pm

battlelava wrote:Would this type of syringe work.
Only if you cut your nails ;)
hectmarr wrote:You have to make many weapons, because this field is long and short life
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battlelava
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Sun May 06, 2012 4:59 pm

jackssmirkingrevenge wrote:
battlelava wrote:Would this type of syringe work.
Only if you cut your nails ;)
Omg I didn't realize they were that long. Only dirty bc I was out plying Airsoft. Hygiene aside. I do 12 inch barrel length x 1.9^2 x pie. But that answer isn't metric right. At what point should I convert to metric I tried it with metric only and ended up with 2171.8749 ml (i think) and 3% should be 65.15ml. It doesn't look right to me.

I have green gas, which is propane mixed with a little bit of silicon oil. Would this work or do I need to ghetto rig my propane torch to the syringe
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jackssmirkingrevenge
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Mon May 07, 2012 12:17 am

battlelava wrote:pie
:D
At what point should I convert to metric I tried it with metric only and ended up with 2171.8749 ml (i think) and 3% should be 65.15ml. It doesn't look right to me.
Whoah there.

First off , if you're using propane the correct percentage is 4.19%.

Chamber volume is 34.04 cubic inches, which gives us 557.8mL

If you started with metric it would have been 30.48cm x (4.83cm/2)<sup>2</sup> x π, which is 557.8mL

I'm assuming your chamber is 1.9inch inner diameter, but we use the radius in the equation.

Correct propane volume to meter is therefore (4.19/100) x 557.8mL which gives us 23.4mL
I have green gas, which is propane mixed with a little bit of silicon oil. Would this work or do I need to ghetto rig my propane torch to the syringe
Technically it should work. Another option is a butane lighter refill can, you should be able to get one cheaply.
hectmarr wrote:You have to make many weapons, because this field is long and short life
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battlelava
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Mon May 07, 2012 1:11 pm

jackssmirkingrevenge wrote:
battlelava wrote:pie
:D
At what point should I convert to metric I tried it with metric only and ended up with 2171.8749 ml (i think) and 3% should be 65.15ml. It doesn't look right to me.
Whoah there.

First off , if you're using propane the correct percentage is 4.19%.

Chamber volume is 34.04 cubic inches, which gives us 557.8mL

If you started with metric it would have been 30.48cm x (4.83cm/2)<sup>2</sup> x π, which is 557.8mL

I'm assuming your chamber is 1.9inch inner diameter, but we use the radius in the equation.

Correct propane volume to meter is therefore (4.19/100) x 557.8mL which gives us 23.4mL
I have green gas, which is propane mixed with a little bit of silicon oil. Would this work or do I need to ghetto rig my propane torch to the syringe
Technically it should work. Another option is a butane lighter refill can, you should be able to get one cheaply.
I just tried the syringe fueling, hit the trigger and then nothing. I retried again, nothing. I checked again to make sure i was using correct ml of propane. Nothing. Sprayed quick burst of carb cleaner and it went off first hit. :shock: Idk whats up with this cannon.
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jackssmirkingrevenge
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Mon May 07, 2012 1:29 pm

video of what you're doing to fuel? are you sure the measurements are correct? are you venting between shots?
hectmarr wrote:You have to make many weapons, because this field is long and short life
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battlelava
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Mon May 07, 2012 2:47 pm

jackssmirkingrevenge wrote:video of what you're doing to fuel? are you sure the measurements are correct? are you venting between shots?
I did it exactly like it was done in the syringe pages video. In between injecting fuel (because i have a 10ml syringe) I placed the cap on the end and only removed to inject more fuel. I did 2 10ml injections and 1 3.5ml injection. I then waited for the fuel to mix. In between shots I took out the projectile, sprayed the air duster through it and left it there for roughly 5 minutes to completely air out.

I was so let down, and its probably a stupid problem too.
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Mon May 07, 2012 4:50 pm

You may be loosing too much fuel with the multiple openings of the chamber.

It looks to me like that syringe should be able to hold at least 12 ml. Measure and mark lines for 11 and 12 ml based on the distance between the other gradations. That should let you fuel with just 2 injections instead of three.

Do you have a needle on the syringe? You want the fuel injected well away from the opening, otherwise too much'll piss out. If you loose just 25% of the fuel your ratio will drop below 3%, which is below the combustibility limits of propane in air. You can use a couple inch long piece of tubing on the syringe to get the fuel well down into the chamber.

A bigger syringe would be better. Try a farm supply store that has horse, cow, pig, ... supplies. They'll have 60ml syringes and blunt tip needles for about a buck each.
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