SpudFiles

Hey Everyone, I am going to be building a cannon soon and need some help. (I have made minis before but not the big boys.)

I have some spare 4 1/2 inch PVC about 6 feet long.
I want to use that as the Combustion Chamber.
Then I want to buy some 2 inch PVC and 1 1/2 inch PVC for the barrel.
Along with a 4 1/2 to 2 inch reducer(if they make them)
and a 2 to 1 1/2 inch reducer. Also a screwcap thing for the chamber.

How big do I need the Chamber to be?

How long will all the PVC have to be for the barrel? (2 inch & 1 1/2 inch)

How big do you want your cannon? If your asking what you can do with it, use the 6 foot 4" pipe for a chamber (yes, the whole piece). Then make a C:B ratio (don't ask, search) that is equal to or near 0.8:1. Add a fan, propane injection, stun gun ignition, ball valve exhaust, then shoot some 'taters.

Whoa well not that big! lol...

I want it to look like this:


(Sorry for the bad Quality, just Click the Picture.)

And I want it to be like 6 foot total.

Also, I wanted it to go from the 4 1/2 chamber, to the 2 inch, to the 1 1/2 inch.

EDIT: Another thing, I want it to go Far, High, Fast, all that.
and I want it to be loud but not "have to wear ear plugs" loud.

EDIT: Another thing, I want it to go Far, High, Fast, all that.
and I want it to be loud but not "have to wear ear plugs" loud.

Then do what hubb said and use the whole size for the chamber
Otherwise your plan looks pretty good, so just do some research (if you havent already) to find out about propane meters, ignitons etc before you go ahead; its a sure recipe for a decent cannon

I am confused, are you trying to run the 1 1/2 inch barrel inside (sleeved in) the 2 inch or does your actual barrel design step up in size.

If the barrel actually gets larger inside as it get closer to the combustion chamber you are going to have problems. You see, the potato or what ever poor item you deside to relocate needs to fit tight in the 1 and a half section. If you muzzle load and push the tater back too far it falls free into the 2 inch section and you will never get it back out.

Also if this is the case you will see a huge performace drop off with all that extra space between the combustion and projectile (called dead space). I would suggest building the cannon so it will accept mulitple barrels, if that is your bent, or picking a barrel (1 and a half works well with almost all potatos) and stick with it for the whole gun.

Also, check out the cannon showcase forums. Seeing other cannons will help you understand designs, as well as, see what other spudders think of various designs.

Another thought would be to construct a coaxial pneumatic. This would allow for more power, smaller size, and more predictable shots.

williamfeldmann wrote: I am confused, are you trying to run the 1 1/2 inch barrel inside (sleeved in) the 2 inch or does your actual barrel design step up in size.

it goes from 4" chamber to a 2" barrel to a 1 1/2" barrel.
(I have seen many videos say use 1 1/2" for potatoes.)

williamfeldmann wrote: If the barrel actually gets larger inside as it get closer to the combustion chamber you are going to have problems. You see, the potato or what ever poor item you deside to relocate needs to fit tight in the 1 and a half section. If you muzzle load and push the tater back too far it falls free into the 2 inch section and you will never get it back out.

I know, thats why you grab a pole and mark it with your hand on how far to push it.

williamfeldmann wrote: Also if this is the case you will see a huge performace drop off with all that extra space between the combustion and projectile (called dead space). I would suggest building the cannon so it will accept mulitple barrels, if that is your bent, or picking a barrel (1 and a half works well with almost all potatos) and stick with it for the whole gun.

I am going to make 2 barrels for it eventually.

williamfeldmann wrote: Also, check out the cannon showcase forums. Seeing other cannons will help you understand designs, as well as, see what other spudders think of various designs.

I have.

Also, I have a grill replacement kit thingy.

Now I'm confused. Are you going to build it like your diagram shows? If so, I would recommend against it. If you have both 2" pipe and 1.5" pipe, you should go ahead and make two barrels for it. Just get each one to the correct ratio.

Very complete answer, I am glad you checked the showcases, they are full of good ideas and opinions. Research is good.

I still don't understand the reasoning behind your idea of having a stepped barrel. The dead space between the 4 inch combustion chamber and 1 1/2 actual barrel will decrease the performance you were saying you desired. By eliminating the section of 2 inch barrel you will increase your performance.

Like I mentioned and you said you wanted to do, you can make the gun in such a way that the 1 1/2 can screw off the gun and you could put bigger and smaller barrels on the gun using the appropriate fittings to get to your combustion chamber. For instance the 1 1/2 could have a fitting from 1 1/2 to 2 inches that screws into the 2 inch port on the chamber. This would give you the option of a breech loader as well. see below.

The green is the barrel going throught the red fitting that screws into the combustion chamber. By sharpening the barrel edge shown in blue you can uncrew the barrel and shove in a potato while your chamber vents. This design will only work with small barrels for the reason that it needs to go through the fitting and some dremmeling or sanding will be needed to get the barrel to pass through the fitting. Just ask if this doesn't make sense.


EDIT: Spelling and formating (sneaky preview button hiding from me).

ok, I dont really get it but o'well. you dont have to re-explain.

Also, I got the 2" to 1 1/2" idea from this:

[youtube][/youtube]

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I am not gonna do the double barrel whatever that was anymore if it will lessen the performance.

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Can you guys help me make one like that or even better without fancy stuff? (like stungun thingys)

I want a 4 1/2" Chamber. How long should it be for Noise and for Power?
I want a 1 1/2" barrel. How long should it be for best performance?
And I want it to be 5-6 feet long.

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One more thing, when you answer the above question, could you not do the 0.0:0 ratio thing? I dont know how that works yet.
so if you could just give me an estamate size for the 2.

Thanks you guys for all the help.

LOL, the little kid tried to break one of the glowsticks and she's like "It doesn't work!!!"

Okay, that was bad.

Anyway, if it's your first gun, I 'm not sure if it is, but you should build a gun off dimensioned plans.

Happy SPuddin'

Redcoat wrote:LOL, the little kid tried to break one of the glowsticks and she's like "It doesn't work!!!"

Okay, that was bad.

Anyway, if it's your first gun, I 'm not sure if it is, but you should build a gun off dimensioned plans.

Happy SPuddin'

What do you mean?

And I have built a few minis in the past 2 weeks but never a big one like this.

So, how long should the barrel and chamber be?

Hi,

As has been said, about 0.8 units of chamber volume to 1 unit of barrel volume is fine. I once had a 3.5 foot 4.5 inch chamber. It was large enough for a 15 foot barrel!

In your double barrel setup, I assume that the small barrel runs inside the larger one, all the way to the chamber?

Regards
Soren

dongfang wrote: In your double barrel setup, I assume that the small barrel runs inside the larger one, all the way to the chamber?

no. it was gonna go from a 2" to a reucer to 1 1/2".

So, how big of a chamber do I need for a 5 foot 1 1/2" PVC pipe?

(sorry i dont know how to do all that volume and ratio stuff.)

For that barrel at the ideal ratio. You would only need a 8inch piece of 4 1/2 inch. I suggest a larger bore.