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My first potato gun and topic

Built a combustion cannon? Then post it here! This section is for completed, finished cannons that you have built. Please include pictures and information.
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My first potato gun and topic

Unread postAuthor: ArtV8 » Wed Feb 11, 2009 9:08 pm

Hi fellows from around the world, this is my first topic @ SF so Ill introduce myself here. My name is Arthur, 20 years old and I live in Rio Grande do Sul - Brazil.

Here I show my first potato cannon, and I'm not sure if its possible to do it with a video, so if it is not allowed just tell me.
My cannon specs are:

100mm chamber x 600mm long
50mm barrel x 1500mm long
3x spark from a stun gun
2 ventilation holes
fuel used was Glade and ammo was regular potatoes
It shots in a distance of 200m

Whem I get some time Ill post some photos showing details and if I get the plumbing parts Ill make a new one using a ventilation fan.
Hope you guys enjoy it.

http://www.youtube.com/watch?v=sQmGpYo6IUc

Just took some pics of my cannon that shows it from dif angles, they also show the 2 ventilation holes (1 @ the end cap and other @ the reduction).
I know theres some extra duct tape over there, but its a test version to see how it works, next one ill try to make a more "clean look"
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Attachments
3x spark.JPG
Spark system that goes inside the chamber
DSC04172.JPG
Thats me holding my cannon, just to show its size.
DSC04173.JPG
Back view of my cannon
DSC04174.JPG
Back view, here you can see the back ventilation hole and the spray can holder on the right side.
DSC04175.JPG
Nice view.
DSC04179.JPG
Here you see all the chamber, the spray can holder with the can atached, the black stun gun above.
DSC04180.JPG
Here is the end cap ventilation hole.
Last edited by ArtV8 on Thu Feb 12, 2009 12:25 am, edited 3 times in total.
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Unread postAuthor: SpudsMcGee » Wed Feb 11, 2009 9:17 pm

Looks cool, does it really have that much of a kick with just Glade as your fuel.

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Unread postAuthor: ArtV8 » Wed Feb 11, 2009 9:25 pm

Thank you.

Yes, its really kicks like that. My little brother(14) that was filming wanted to shoot once, and I let him do that.
It almost got of his hands \o\

Probably tomorrow I'll make some shoots and take pics whem my camera batery loads.
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Unread postAuthor: Radiation » Thu Feb 12, 2009 12:53 am

Welcome to Spudfiles! It's a good start. I like the look of the gun. Generally over under designs are harder to get right and it looks like this gun functions very well!

There are a few potential safety concerns. First This:

Image It is obvious that the hole you drilled and put in the bottle cap in is not sufficiently sealed (thus the burn marks) you are literally burning a larger and larger hole every time you light your gun off.

Second the very use of bottle caps as a ventilation system is poor practice as these caps are very weak, you are drilling through your PVC in a weak spot and putting in a weak cap... Well let's just say you are inviting a major blow out and hopefully nobody is in the way when it happens. (I can tell you based this gun off the Monkey Base guys design)

Last is that PVC pressure rated? Many accidents have happened resulting from people using none pressure rated materials.

Please don't take this as criticism, these are valid concerns for your safety and should be treated as such. This is a great start though, it is obvious you understand the concepts necessary to build a moderately complex gun! Great first post.
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Unread postAuthor: inonickname » Thu Feb 12, 2009 2:47 am

Inspired by this guy I think?
If you use somebody's design, always best to give credit.

Nice gun, but ditch the bottle caps and replace them the threaded pvc stuff. The bottle caps are bad, I think I've seen someone even use them as burst disk before.

Still, nice sweet work.
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Unread postAuthor: mark.f » Thu Feb 12, 2009 9:59 am

Ehm, you can't own a basic design like this. That's like me saying "I've built an inline combustion with a 4x12" chamber and a 2x54" barrel before, therefore anybody else who builds the same thing is stealing my idea."

Also, the bottle cap, properly attached (through a double layer of PVC) with the proper threads (probably part of an aluminum threaded bottle, which do exist), would be perfectly fine.
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Unread postAuthor: ArtV8 » Thu Feb 12, 2009 12:03 pm

Yes you guys are right, and actually I forgot to thank TheBug and MushiYoshi for their tutorial @ youtube, Ill do that later.

Radiation:

This pvc is none-pressure rated, thats why i covered it with that extra muffs on the middle of the chamber, the muffs are much stronger than the tube so theres no way for the tube explode there using simple fuel, It is easier to explode where the area is smaller because It creates more pressure (bottle holes for example)
The problem with that bottle cap, especially, happened because I barely sealed the hole inside the chamber that is the right place to do it. Luckily that problem appeared to this test version, now I can understand the forces and correct for the next versions. The same happened to the little holes I use to get the wires to the spark system and I'll fix using screws instead of pass the wires through a hole.
All these improvements will come in the next version and also I'll use a chamber fan and high pressure pipes that I'll get with a friend that works @ my city water department.

Hope more people comment, thats good for me to increase my knowledge.
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Unread postAuthor: Pilgrimman » Thu Feb 12, 2009 12:19 pm

It is easier to explode where the area is smaller because It creates more pressure (bottle holes for example)


It is more likely to explode where there is a LARGER surface area! Pressure=Force/Area. The reason the bottle holes are unsafe is the fact that they are thinner then most PVC, and are glued in.

Very nice cannon however. Glad you're taking our hints and learning from your design flaws. The cannon functions just fine, however! :twisted: :twisted:

Hope to see more from you!
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Unread postAuthor: Radiation » Thu Feb 12, 2009 12:36 pm

Ok I'm glad you're open to suggestions. Ditch the pop bottle stuff all together, it's bad practice and quite honestly ball valves are much easier to use for the purpose of chamber venting and cheap to acquire. Never drill a huge hole like you have through a fitting such as a reducer. Use pressure rated PVC and, this is important, pressure rated fittings. The reducer you used does not appear to be pressure rated AND it has a giant hole drilled in it.
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Unread postAuthor: ArtV8 » Thu Feb 12, 2009 12:58 pm

In fact theres no chance for the bottle caps fly out because I put them from inside to outside so the combustion press it against the chamber wall. What I made wrong was the silicone, I should have used something more powerful and designed to hold high temperature.

While I use simple fuel and no chamber fan @ this cannon it'll be safe i guess.
For the next cannon I found some pipes that hold 7.5 BAR or 110 psi. Do you guys know how much pressure one of these aerosols can make?
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Unread postAuthor: psycix » Fri Feb 13, 2009 7:59 pm

Silicone or hot glue cant seal presssurissed stuff. You'll need something like epoxy.
That spark gap is WAY to big. They should be less then a few mm added up to eachother. Im surprised that it actually works this way.

I bet that that air wick stuff gives the cannon a real flowery smell. :)
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Unread postAuthor: ArtV8 » Fri Feb 13, 2009 9:35 pm

hahah but I like air wick smell in the morning xDD

Now I added some epoxy to the bottle caps and where the wires get in the chamber, its working just perfectly and shooting around 200-250 meters.
That photo of the spark gap I took whem I made it, and it didn't work on first test. After that I replaced the screws and now it makes a huge and constant spark.

Im making some plans for building a propane gun. Im just studying a little to know more about C:B ratio for this kind of weapon (mine uses 1.5:1 CB ratio). I'll make a normal size using 110mm high pressure pipe and a 50mm barrel with propane and if it works like I want Ill make a monster one using 150mm chamber and 75mm barrel.
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