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Making the process a bit easier

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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Making the process a bit easier

Unread postAuthor: CS » Sun Sep 23, 2007 6:20 pm

In chase of the ever elusive goal...

For me I find both the loading of the projectile, and the venting of the chamber two slight annoyances.

Today I am not so much concerned with the loading of the projectile, rather a less annoying means of venting the chamber. When venting all you are doing is swapping oxygen rid air, with oxygen rich air. As the oxygen was burnt off as a result of the combustion.

air - don't confuse with oxygen the gas, rather the collection of gases in a defined space, or the surrounding atmosphere.

The atmosphere contains ~20.9% oxygen, and the atmospheric pressure is ~14.7PSIA. So the venting process could be simplified by injecting ~3.1PSI of pure oxygen. In fact I have easy access to regulated oxygen, however we all know the dangers of handling pure oxygen. Although you could inject ~14.7PSI of compressed air, and get the desired amount of oxygen contained in the ~20.9% of the air. As noted below the chamber would need to be closed, implementing a burst disk, or similar device. That only detracting to the elusive goal of ease.

[note - the chamber would need to be closed for discussed methods to work. as well compensation for spent gasses in the chamber were not made.]

Or after the shot you could emit short *puffs* of air into the chamber in a attempt to blow spent air out the barrel. But in reflection that probably wouldn't work as not all the spent air would be exhausted. That resulting in a unpredictable amount of oxygen in the chamber, which gives you nothing to base your propane calculations on.

Why not just build a pneumatic, or use the common means of venting? Well I would like to build a metal combustion, and weld it shut. Any help is much appreciated!
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Unread postAuthor: Dornep » Sun Sep 23, 2007 6:38 pm

My ideas would be..

#1: Use an external venting setup like an air mattress pump with a hose connected to a small fitting.

#2 You could use a vacuum cleaner to suck the spent air out of the chamber via a small fitting.

#3 If portability isn't a factor you could rig up a blow gun with a long wand to stick into the chamber via the barrel and blow the spent air that way.

#4 Or you could wait an hour between each shot.

Edit* If your going to be welding it all together would it be impossible to use threaded chamber pipe so you could have access to the chamber using a steel cap?
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Unread postAuthor: thespeedycicada » Sun Sep 23, 2007 6:48 pm

here what about this please pardon the handwriting and drawing i did these in the car.Heres how it works you fire the gun then you push the combustion byproducts out of the chamber and through the barrel then pull the piston back and sucking in fresh air.Hope this helps! sorry the pics came out backwards just read from the bottom up.
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P1010131.JPG
FIRE!!!
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vent.
P1010132.JPG (34.92 KiB) Viewed 873 times
P1010133.JPG
bring in fresh air!
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Unread postAuthor: Dornep » Sun Sep 23, 2007 7:05 pm

I also had a piston idea but that would make the ignition setup overly complex.. BTW how do you plan on igniting this beast Pimpmann?

If you used the plunger setup all your fittings would have to be perfectly flush with the chamber wall and you would probably have a thin rod sticking out the back of your cannon depending on how you designed it.
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Unread postAuthor: CS » Sun Sep 23, 2007 7:13 pm

Thank you for the responses thus far.

Dornep, I have considered a air mattress pump, however they tend to be bulky. I considered a small PC centerfugial blower as a possible option. But if possible I would like to avoid any electronic components.

The mechanical operation of threading is one that I dislike, if at all possible I would like to avoid it. To get a decent seal you have to use some medium in between the threads, and its a time consuming operation in the first place.

Thespeedycicada, I first thank you for taking the time to draw up your ideas! I like how its one simple mechanical operation. The biggest problem I can see is the seal between the rod, and the cap. As well this rod will protrude another chamber length out proving inconvenient. Simple in design, the implementation of it will be a bit more tedious.

:Addition:
Dornep brings up a good point I didn't even consider. I would never intend to make the ignition flush with the chamber walls, as it would be both ridiculous, and reduce performance. I intend to use a small spark plug with a stungun. (already got the stungun)
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Unread postAuthor: mopherman » Sun Sep 23, 2007 7:24 pm

you could put a small bike pump at the back of the camber and a small ball valve at the front of your chamber. then you could open the valve and pump out unwanted gasses.
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Unread postAuthor: Dornep » Sun Sep 23, 2007 7:25 pm

Maybe you could use a plunger attached to your ramrod if it's a muzzle loader.

With a threaded hole in the end of the chamber you could push the plunger down the barrel pushing the majority of the spent air out. Then when you remove the ramrod you suck fresh air in... As long as your C:B ratio was 1 to 1 or below say... 0.8 to 1, I see no reason why you couldn't push all the spent air out of the chamber...

Maybe you could draw up a schematic thespeedycicada... :D

edit* it would be cumbersome if your one of those guys that has to have a breech loader but it might work...
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Unread postAuthor: thespeedycicada » Sun Sep 23, 2007 7:49 pm

how about this will it affect performance much? you could either put it where the reducer is the piston cant reach it or make a little protrusion comin out of the camber and put the ignition there as for the sealing don't seal the hole where the rod comes out you wouldn't be able to move it! just seal the piston with o-rings.If these suggestions will hurt performance ill try and come up with something else sorry but i don't know much about combustions! :)
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How about this.Once again sorry about the quality!
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Unread postAuthor: Dornep » Sun Sep 23, 2007 7:56 pm

The only real problems I see with the piston in the chamber idea is..

1 If he is welding this gun together I doubt he will be using steel bell reducers.

2 You can't really exhaust the whole chamber without removing the barrel after each firing. When you push the plunger it will push the spent air into the barrel and not completely out of the gun. When you pull the plunger back it's going to suck that same spent air that's in the barrel back into the chamber.
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Unread postAuthor: thespeedycicada » Sun Sep 23, 2007 7:59 pm

Any reducer that comes out of the barrel will do or just put the barrel a few inches in the chamber and make it co axial.And i gave him two options for ignition the reducer and the chamber protrusion and im guessing the barrel will only take a couple of seconds to vent and if it doesnt it shouldnt have to much of an impact on combustion.
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Unread postAuthor: Dornep » Sun Sep 23, 2007 8:50 pm

Ok I've drawn up a little schematic of my own.

If you were designing this cannon speedycicada and insisted on using the plunger design, I think this would be the easiest way. Wiring up your stun gun to opposite rods of the plunger and using large washers you could create a spark gap ON the plunger.

You would still have the bulky rods sticking out the back of the gun.. This would mean you couldn't fire the cannon with the rear cap on the ground and it would make any gun look hella retarded.. but here it is.

Just had a eureka moment... If you made the plunger with a metal base you could use an extendable magnet pen to push and pull the piston.. Then pull the magnet off and your good to go.
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Unread postAuthor: thespeedycicada » Sun Sep 23, 2007 9:05 pm

I think what we are discovering is that if you want to do this you either have to give up simplicity or give up compactness i personally dont care if its only a little more bulky than usual which is why i like my plunger idea its simple and i think you are a bit over exagerating about its bulkyness anyway enough with that idea you guys obviously dont like it what if you made a piston to go around the barrelmade it so it sealed and made the barrel moveable just pump it a few times and you are vented! ill try and post a pic soon.
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Unread postAuthor: Dornep » Sun Sep 23, 2007 9:11 pm

I'm not trying to shoot down your idea bro, I'm just pointing out it's weaknesses. It has it's strengths but I think it would be better utilized on a PVC cannon. In the end it's Pimpmann's cannon and we can only offer suggestions.

I'm looking forward to the drawings of your pump action idea though.. :wink:

edit*** Pimpmann do you by any chance have a design for this cannon? If so could we get a sneak peak or schematic?
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Unread postAuthor: HaiThar » Sun Sep 23, 2007 9:30 pm

basic idea maybe?
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The shradervalve in this diagram represents some sort of vent valve. As for the inlet for new air, I have no idea what you are going to do...
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Unread postAuthor: HaiThar » Sun Sep 23, 2007 9:31 pm

thespeedycicada wrote:how about this will it affect performance much? you could either put it where the reducer is the piston cant reach it or make a little protrusion comin out of the camber and put the ignition there as for the sealing don't seal the hole where the rod comes out you wouldn't be able to move it! just seal the piston with o-rings.If these suggestions will hurt performance ill try and come up with something else sorry but i don't know much about combustions! :)


You got to get PVC designer m8 ;D. Let me give you the link.
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