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what did i do wrong, what should i do now?

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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what did i do wrong, what should i do now?

Unread postAuthor: jct0064 » Fri Mar 20, 2009 12:07 am

I made a cannon the other day:
Barrel: 2" diameter 48" long (volume: 150.80)
Chamber: 4" 18" long (volume: 226.19)
C:B ratio is 1.5:1
I shot it and then walked out the distance (107 yards)
I am using right guard as the fuel
It is made of pvc sch-40 pipe, can it hold up to propane (i heard it was a bad idea, but it seams to be the method of choose here)

Did anyone notice design flaws?
I was considering changing to propane;
installing a propane meter, pc fan, and/or a stun gun multiple spark strip thing. Could you estimate the distance gain and relative cost of each of these?
It would be a great help
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Unread postAuthor: pharmboy » Fri Mar 20, 2009 12:13 am

Metered propane would be a definite upgrade, and it can be done cheaply if you source your parts correctly. It would certainly improve your consistency from shot to shot, if not just improving distance, as would a chamber fan. Ignition, again it's a matter of how you source your parts, whether you buy a cheap stun gun, or salvage some disposable cameras. Nice to see someone getting off to a good start.
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Unread postAuthor: starman » Fri Mar 20, 2009 12:28 am

Are you shooting potatos? Don't count on lots of performance improvements. You have around a 200-250 yard limit because of drag and irregular shapes, no matter how powerful a cannon you apply to the job. Anyone that tells you significantly higher numbers is "exaggerating".

You should be able to do better than 107 yards though. 1.5" barrels are preferable to 2" for spuds and can usually produce a little more distance....simply because the spud slug is a little smaller and more uniform.

If you decide to go for a full advanced combustion, I would recommend moving to a more reliable hardened ammo to realize its full performance. There are many choices of which golf balls invariably rise to the top.
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Unread postAuthor: jct0064 » Fri Mar 20, 2009 12:39 am

Thank you for the tip, the barrel is removable so i can install a 1.5" barrel. Is it even a remove fear that a pvc sch-40 gun could blow from a propane ignition? What are your longest distance with an advanced combustion gun what features did it have, what ammo, and fuel where you using? Sorry if I sound like a interrogator.
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Unread postAuthor: starman » Fri Mar 20, 2009 1:21 am

Go read up on my Triple Thunder Cannons, a fairly feature filled example.

I can get ~700 fps golf balls and range in the 1/2 mile + zone. I haven't been able to get an exact measurement as the balls easily fly out of sight very quickly. I use metered propane or MAPP gas.

Propane doesn't offer that much more energy than what you get from Right Guard but does offer a more precise metering capability and a much cleaner burn. Sched 40 PVC holds up well to 1x propane shots.
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Unread postAuthor: jct0064 » Fri Mar 20, 2009 1:35 am

What do you mean by "1x" propane shots? would it be stable for me to put a pair of screws on either end to make two sparks?
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Unread postAuthor: starman » Fri Mar 20, 2009 1:42 am

jct0064 wrote:What do you mean by "1x" propane shots? would it be stable for me to put a pair of screws on either end to make two sparks?


A 1x refers to a standard non-pressurized (non-hybrid) fuel load, 1 atmosphere of air. Of course you could use the screws as long as you put them through 2 layers of PVC, through a coupler for instance. Try not to ever drill holes in a single layer of pipe. Try to get your gaps as close to the center of the chamber as possible.

BTW, it would help greatly if you were to post photos of your cannon as you ask questions about it.
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Unread postAuthor: jct0064 » Fri Mar 20, 2009 1:56 am

This is probably a dumb question, but what is a burst disk? How long can i make a 1.5" barrel? And i was wondering if i could make two sparks with one of those spark plug looking Bbq lighters?
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Unread postAuthor: grock » Fri Mar 20, 2009 2:07 am

couple things.
first off, a burst disk is an extremely fast way to vent the chamber into the barrel, and is usually a square of aluminum. it ruptures at a certain pressure, releasing the gas. if you put multiple sparks in your chamber, make sure that they are wired in series, not parallel, otherwise it will jump the closest gap and one have one spark. and you CAN make a 1.5" barrel as long as you want with couplers, but the optimum chamber to barrel ratio is between .8:1 and 1:1, but im sure ill get corrected on that. just a heads up, you wont be shooting any golf balls out of 1.5" pvc, they are slightly too big. a perfect barrel for golf balls is1.5" SDR 21, which happens to be closer to 1.7" for some reason im not sure of. in any event, it works great for golf balls.
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Unread postAuthor: starman » Fri Mar 20, 2009 2:09 am

OK, I get the feeling you need to be doing a little more homework and study on your own here. All of this info is available on the site and others...all you have to do is search...the Wiki button at the top. You can also use the search link. Here's Burst Disk to get you started. Also, the Trip Thunder write-up is chocked full of this kind of info.

These questions are getting mightly close to spoon feeding which something we don't like to do at Spudfiles.
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