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mini potato gun (help)

Discuss miniature cannons built from things such as pill bottles and pen caps.
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mini potato gun (help)

Unread postAuthor: drunkii » Fri Jul 18, 2008 7:32 am

hiii
this is my new mini potato gun
Image
Image

and this is the 'combustion chamber '
Image

evrything works
when i load the chamber with fuel , i hear a bang , and i see a flame come out of the barrel
thats good
but when i put a potato in the barrel ( a little potato afcorse:D)
it wont work:s
just 1 time it works , and that was by accident xd

and i see a spark in the chamber;)

srry for my bad english im from belgium
ty if u help me
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Unread postAuthor: THUNDERLORD » Fri Jul 18, 2008 7:51 am

I'm more into pneumatics, But the barrel looks a bit large for the chamber.
Maybe try a smaller diameter barrel. (A pen maybe)
Also, what do you use for fuel? 8)
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Unread postAuthor: drunkii » Fri Jul 18, 2008 7:53 am

THUNDERLORD wrote:I'm more into pneumatics, But the barrel looks a bit large for the chamber.
Maybe try a smaller diameter barrel. (A pen maybe)
Also, what do you use for fuel? 8)

normally, you can test if the barrel is good voor the chamber,, you have to shoot without a projectile
and if you see a flame come out of the barrel , the barrel may be bigger
i think it cause i have read it somewhere;)
fuel : hairspray
a pneumatics spudgun , goes that faster than a combustion sg ??
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Unread postAuthor: THUNDERLORD » Fri Jul 18, 2008 8:05 am

a pneumatics spudgun , goes that faster than a combustion sg ??


A mini combustion is more simple than pneumatic one.
But Yes, higher pressure can be used than the pressure generated from a 1x combustion.

I still say try a smaller barrel tube. (like a plastic pen).
If your getting ignition it should fire unless there is insufficient pressure.

Or another possible problem is that hair spray can leave a sticky residue. And maybe that's slowing down the spud.
Try cleaning the barrel with a solvent and use a different fuel maybe.
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Unread postAuthor: drunkii » Fri Jul 18, 2008 8:07 am

THUNDERLORD wrote:
a pneumatics spudgun , goes that faster than a combustion sg ??


A mini combustion is more simple than pneumatic one.
But Yes, higher pressure can be used than the pressure generated from a 1x combustion.

I still say try a smaller barrel tube. (like a plastic pen).
If your getting ignition it should fire unless there is insufficient pressure.

Or another possible problem is that hair spray can leave a sticky residue. And maybe that's slowing down the spud.
Try cleaning the barrel with a solvent and use a different fuel maybe.

O.k , i am going to try it;)
later , i will post it here what is happened
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Unread postAuthor: drunkii » Fri Jul 18, 2008 8:31 am

yes it works ;)
a little bit of hairspray
and i changed the barrel;)
ty :)
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Unread postAuthor: THUNDERLORD » Fri Jul 18, 2008 9:42 am

It's Alive!!!
Cool. Smaller diameter barrel you changed it to right?
Wondering.

That's interesing, the C:B really is for optimizing a particular barrel.
But in a combustion the diameter will the effect pressure output.
Correct...Anyone(?)...

In pneumatic there's also flow restriction.
And with possible use of sabots, It seems harder to optimize (for the same weight projectile as smaller diameter barrel). I am slanting towards sabots out of larger diameter barrels for optimizing pneumatic barrel length especially. (Better configurations) :roll: 8)

EDIT: For example, if I was shooting say, an arrow out of a pneumatic,
I know I prefer a larger barrel with a discarding sabot around it.
But if fired from a combustion a barrel close to the arrow diameter should do better(?)
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Unread postAuthor: drunkii » Fri Jul 18, 2008 11:04 am

THUNDERLORD wrote:It's Alive!!!
Cool. Smaller diameter barrel you changed it to right?
Wondering.

That's interesing, the C:B really is for optimizing a particular barrel.
But in a combustion the diameter will the effect pressure output.
Correct...Anyone(?)...

In pneumatic there's also flow restriction.
And with possible use of sabots, It seems harder to optimize (for the same weight projectile as smaller diameter barrel). I am slanting towards sabots out of larger diameter barrels for optimizing pneumatic barrel length especially. (Better configurations) :roll: 8)

EDIT: For example, if I was shooting say, an arrow out of a pneumatic,
I know I prefer a larger barrel with a discarding sabot around it.
But if fired from a combustion a barrel close to the arrow diameter should do better(?)

sorry my english is a little bit limited;)
im 15 and come from belgium

but check :
That's interesing, the C:B really is for optimizing a particular barrel.
But in a combustion the diameter will the effect pressure output.
Correct...Anyone(?)...

what does the C:B thing means?
combustion chambr --> barrel or something?:p
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Unread postAuthor: nibbler125 » Fri Aug 08, 2008 3:11 pm

try priming close chamber then add potato
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Unread postAuthor: jimmy101 » Fri Aug 08, 2008 6:33 pm

drunkii wrote:but check :
That's interesing, the C:B really is for optimizing a particular barrel.
But in a combustion the diameter will the effect pressure output.
Correct...Anyone(?)...

what does the C:B thing means?
combustion chambr --> barrel or something?:p

For a combustion gun the CB optimises the barrel to the chamber.

Read the CB ratio page in the spud wiki. Basically, the CB is the chamber volume divided by the barrel volume. For a mini, any ratio between about 0.5 and 2 is fine. Ratios outside the range will still work but the performance won't be very impressive.

I suspect your problem has just been getting the right amount of fuel in the chamber. It is very easy to put in too much fuel and the gun won't fire if therre is too much fuel. For propane based fuels (like most aerosols) you want 4% of the chamber's volume as gaseous fuel. So if your chamber volume is 100cc then you need 4cc of propane for optimal performance. If you put in less than 3%, or more than about 8% propane, the mixture will not ignite.

A small syringe and a disposable butane lighter is a great way to meter fuel for a mini. You can get syringes from farm supply stores. For a mini you need a pretty small syringe. Got an inkjet cartridge refill kit? They usually come with a 10cc or so plastic syringe, which works great. For butane the fuel ratio is 3.2% (IIRC).

See the spudwiki page on fuels and this page for how to use a syringe with a disposable butane lighter.
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Unread postAuthor: TwitchTheAussie » Mon Aug 18, 2008 2:11 am

Also try using butane. Use a little bit and swirl it around to give it a better air/fuel mix. Thats the major problem with mini's.
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Unread postAuthor: nibbler125 » Sun Aug 31, 2008 8:35 pm

try adding fuel first then add the projectile
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