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New cannon.. Want to discuss aspects of it.

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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New cannon.. Want to discuss aspects of it.

Unread postAuthor: anixon88 » Sat May 19, 2007 4:30 am

I've build a combustion before, just your regular BBQ igniter and spraying Butane or releasing propane into the chamber and capping it.

Now im looking to building a Propane injection, based on plans from this page http://www.spudfiles.com/forums/complete-plans-for-advanced-combustion-t4512.html
Im going to be using ABS material
i plan to use a BBQ Sparker that sparks about 5-10 times per second

I am wondering about what diameter of barrel i should use...

my chamber size i think is going to be 15"x4"
i guess thats not including the ball valve for venting and the elbow joints

how long should the piping for storing the propane at the right pressure and such before sending into chamber?

I think thats all i can think of..
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Unread postAuthor: super spuder » Sat May 19, 2007 8:51 am

you have a chamber volume of 188.5714285714284. and aproxamatly 4 % should be propane. so you need 7.542 cubic inches of propane. now what size of pipe do you want to use for the metering pipe? and as for the pressure, that is just a guessing game once you get it built
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Unread postAuthor: SpudBlaster15 » Sat May 19, 2007 12:11 pm

super spuder wrote:and as for the pressure, that is just a guessing game once you get it built


Wrong. The pressure can be calculated very easily if you know your chamber volume, and your meter pipe volume.

Since you have already decided upon a chamber volume, choosing a meter pipe volume is your next task. 1/2" steel pipe is a good size to use. Since you are using a meter style that utilizes a pressure gauge mounted in the center, I know from experience that 2 3" long pipe nipples create an ideal meter length to fit on your chamber.

Once assembled, you are left with a meter volume of 3.25 cubic inches (as per fluid volume measurement). Including the ball valve and 2" elbows, your chamber volume will be ~225 cubic inches. 225*0.042= 9.45, meaning you will need 9.45 cubic inches of propane in the chamber. Now, simply divide 9.45 by 3.25 to obtain your required meter pressure in atmospheres. Multiplying the result, 2.9, by atmospheric pressure in PSIA will give you 42.6, your approximate required meter pressure.

As for the barrel diameter, I would use 1.5" Sch 40 pipe. It is the best choice for launching potatoes.
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Unread postAuthor: anixon88 » Sat May 19, 2007 12:39 pm

Thanks for the info

What is the easiest way to put on handles

and what is the difference for me using a shorter barrel with bigger diameter..
like instead of a 7' x 1.5" diameter being replaced with a 6' x 2" diameter

Are there quick turn and release joints in ABS in order to have a fast breach loading system?
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Unread postAuthor: super spuder » Sat May 19, 2007 1:10 pm

i don't call that easy :lol: a longer barrel will give the object you are shooting more time to build up speed inside the barrel. a good way to make handles would be to have a T sone where along the chamber, and then use the output of the T with a piece of pipe in it as a handle. There is probly better ways, but that is one of them.
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Unread postAuthor: frankrede » Sat May 19, 2007 3:10 pm

super spuder wrote:pressure, that is just a guessing game once you get it built

Wow superspud, you really are a moron.

And using a 6ft 2" barrel and a 1.5" 7 ft barrel is fine.
Seeing that a 2" has more volume anyways
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Unread postAuthor: anixon88 » Sat May 19, 2007 3:23 pm

I was wondering what the differences between using one or the other.. i havent really looked into barrel interchangability
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Unread postAuthor: super spuder » Sat May 19, 2007 3:26 pm

Frankred, congratulations, you made it into my signature :D , and sorry, but i had never seen that formula before, now i know.
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Unread postAuthor: SpudBlaster15 » Sat May 19, 2007 3:40 pm

anixon88 wrote:I was wondering what the differences between using one or the other.. i havent really looked into barrel interchangability


Assuming you are using an ammo of fixed density, the 1.5" barrel will give you more muzzle velocity, greater range, and more impact energy density. The 2" barrel will give you more overall muzzle energy.
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Unread postAuthor: frankrede » Sat May 19, 2007 6:40 pm

super spuder wrote:Frankred, congratulations, you made it into my signature :D , and sorry, but i had never seen that formula before, now i know.
I wonder if you have began to realize why we have all said that about you?
I don't think its a coincidence.
You go out and give people advice on subjects you have no knowledge about.
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Unread postAuthor: super spuder » Sat May 19, 2007 7:01 pm

Well, i tell people what i know to the best of my knoledge, sorry but i did not know there was a formula to figure out what the presure has to be in the regulator. Only 2 of thoes are from me being wrong about something, and one of them was really late at night, so i am sorry, but i was just answering to the best of my knoledge, and obviusly that was not good enough, but one thing you have to realize, not everyone knows everything, and now next time someone ask's how much pressure needs to be in the regulator pipe, i will know how to figure it out.
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Unread postAuthor: anixon88 » Sat May 19, 2007 10:18 pm

Well i bought all my initial ABS stuff and have it fitting together
I have a couple more questions..
I have a 4" -> 3" converter and then a 3" -> 1.5" and then ill be screwing on a PVC valve very much like the one in the design.
now im wondering if i can use some small screws and screw instead of glue the 4" -> 3" reducer in order to allow easier access to the chamber.

And i was also running into troubles figuring out how to securely fix the 1/2" steel piping into my chamber.

Here is a picture of what i could fit together

The chamber i made to 16" long x 4" diameter
the barrel i ended up making about 88" long x 2" diameter
Image

any input is totally welcome
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Unread postAuthor: SpudBlaster15 » Sat May 19, 2007 10:40 pm

Screws can be used to hold the reducer onto the chamber. The force exerted on the fitting is nowhere near enough to compromise the joint should you choose to use this method.

To install the 1/2" pipe nipple, buy a 1/2" NPT tap, and use it to thread a hole drilled into the side of the chamber.
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Unread postAuthor: frankrede » Sun May 20, 2007 12:09 am

super spuder wrote:Well, i tell people what i know to the best of my knoledge, sorry but i did not know there was a formula to figure out what the presure has to be in the regulator. Only 2 of thoes are from me being wrong about something, and one of them was really late at night, so i am sorry, but i was just answering to the best of my knoledge, and obviusly that was not good enough, but one thing you have to realize, not everyone knows everything, and now next time someone ask's how much pressure needs to be in the regulator pipe, i will know how to figure it out.
If you can't answer the question right, then why bother?
huh? Have you even built a propane meter before?
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Unread postAuthor: anixon88 » Sun May 20, 2007 10:13 pm

Well i did more today
its almost done :D

here are some updated pictures.
i didn't really have trouble getting the steel pipe fixed into the barrel
Image

Although i am a little worried about the barrel size.. it is quite heave and might need support, though im not sure how to do it and still have the barrel removable for ease of movement and storage
im thinking about cutting it down to about 6ft
possibly also having a second barrel at 1.5" with an increase and a 2" screw to fit on
Image
a closeup of my mess of cables for testing all the electrical out
Image
Image
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