Advanced Combustion Potato Gun

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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LCTChamp
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Sat Nov 01, 2008 12:50 pm

This is my first advanced combustion. After playing with a spray n pray combustion I decided I needed more power, so this is what I came up with. I will try to get a video up later.

Specs:

Chamber: 4" x 18"
Barrels: 2",1 1/2, 1" all x 36"
Ignition: Grill igniter
Fuel: Metered propane
Venting: 4" screw cap and fan
Ammo: whatever fits in the barrel


Future upgrades:

Flat black paint job
Switch for fan instead up plugging it up every time.
Propane holder.
Electronic box to hold battery and switch.
Golf ball barrel
Ball valve vent
Install another spark gap
Attachments
The chamber, meter, and grip.
The chamber, meter, and grip.
The whole gun
The whole gun
The whole gun again
The whole gun again
Last edited by LCTChamp on Sun Nov 02, 2008 8:00 am, edited 1 time in total.
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Ragnarok
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Sat Nov 01, 2008 1:14 pm

Looks decent enough - there are a few grubby marks on it, but that won't affect it's performance.
The one thing I would say is that the pressure gauge on the meter is of little use unless you've actually got a regulator in your propane feed.

Other than that, it seems to be a very passable effort. Good job :)
Does that thing kinda look like a big cat to you?
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VH_man
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Sat Nov 01, 2008 1:21 pm

Rag, i think he simply opens the ballvalve slightly and closes it when the desired pressure is reached, negating the need for a Regulator. Its an idea i was thinking of for some time.

That and sweet Ballvalve... Its very... Sliver.
EphOph
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Sat Nov 01, 2008 1:43 pm

Even doing it that way induces some error and inconsistency. However, it is possible to do it without a regulator if the meter built to fill at tank pressure (which still varies according to local temperature and atmospheric pressure). The best way is to use a regulator so you know you're getting the right amount every time without having to time it.

Nice gun, I like it. An upgrade you didn't mention is something on the back cap to help with venting. Most people use a 1" (or bigger) PVC ball valve, but other options are available too. Such an upgrade is very convenient as it is much easier and quicker to open a ball valve than to unscrew the cap every time.
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LCTChamp
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Sat Nov 01, 2008 7:45 pm

VH_man you are right but as ephoph said it is somewhat incosistent. I didn't have the money to buy a regulator so I did it this way. The ball valve happened to be laying in my garage. I think it looks cool.

Ephoph I forgot about the ball valve vent. I will do that as soon as I have the time and money.
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starman
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Sat Nov 01, 2008 9:31 pm

VH_man wrote:Rag, i think he simply opens the ballvalve slightly and closes it when the desired pressure is reached, negating the need for a Regulator. Its an idea i was thinking of for some time.
It's very difficult to do this with any consistancy at all. Even small controlled bursts allow the meter to fill up to max pressure in no time, especially with a new propane canister.

Ictchamp, save up $20 and install a regulator on that propane tank. You'll be glad you did. BTW, a good job on your first advanced. Do you care to show us the your spark gap(s), fan and internals?
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LCTChamp
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Sun Nov 02, 2008 8:05 am

Starman actually it is pretty consistent. If you open the ball valve barely it wont over pressurize. And if it does I turn off the propane open the valve back up and the pressure will go down because of a leak I have. The leak is actually a good thing :).

Edit: I only have one spark gap and just a regular cpu fan that is friction mounted its not too interesting, but ill see what I can do.
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