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My very first combustion

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 very first combustion

Unread postAuthor: auxiliary » Sun Oct 12, 2008 7:11 pm

I built this cannon a couple of months ago because I had some spare cash and nothing to do with it, so I decided to build my first combustion. Before, I built a sprinkler valve pneumatic and a high pressure spring loaded ball valve pneumatic. Ever since I've built this cannon I've now been mainly interested in combustion cannons. I just love the easy power and quick refueling (no bike pump hassle). So here are the basics of my cannon:

Chamber: 3" ABS w/ DWV fittings
Barrel: 1 1/2" ABS
Fuel: Metered propane
Ignition: Duel spark Chamber Short w/ BBQ igniter
Venting: 2" Ball valve and 60mm fan w/ 9v power supply
Ammo: Round white potatoes or Purple potatoes

You guys are probably wondering how I attached the ball valve so here's my explanation... the ball valve is PVC cemented to a 2" piece of PVC pipe which runs pass a modified 2" ABS bushing. On the other side of the bushing inside the chamber, is the other half of the ball valve that was sawed off. This is cemented onto the 2'' PVC pipe on the other side of the modified ABS bushing. This can be thought of as securing a bolt by screwing on a nut on the other side of a piece of wood. The 2" PVC pipe is glued to the the ABS bushing surrounding it with JB Weld.

One thing I like what I did was how I stored all of the electronics. I managed to stuff the BBQ igniter, fan switch, 9v battery+holder,and the ignition and fan electrodes. I did all this without having a spark from the igniter jump, by dividing the entire pipe with a bit of thin poplar wood. To secure the electrodes (small bolts that go into the chamber) I had to drill on the other side of the pipe so I could use a screw driver and that is why I have a section of 1 1/2" ABS pipe over the electronics tube.

About the propane meter... The operation is a little different because you open the first valve and fill it to about 66psi, then you shut it and open the second one. I made it just a tad bit bigger so 66psi is the optimal meter pressure. This helps on colder days.

Here are the pictures:

With there being no handle on the gun, it might look as if it would be awkward to hold, but actually it is held like a rifle. I put the ball valve against my shoulder, then put my left hand on the propane tank and with my right hand I reach for the BBQ igniter.
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cannon picture that got left out.jpg
Here's the other side with propane meter
cannon picture that got left out.jpg (26.57 KiB) Viewed 2536 times
First combustion cannon 002.jpg
Here is the side showing the electronics tube, igniter, and fan switch
First combustion cannon 002.jpg (21.91 KiB) Viewed 2536 times
chamber short 002.jpg
Here is the inside of the chamber where you can see the chamber short on the left and the electrodes and spark gaps on the right
chamber short 002.jpg (18 KiB) Viewed 2536 times
First combustion cannon 005.jpg
Here is the battery end of the tube where you can see the 9v in its seat
First combustion cannon 005.jpg (16.13 KiB) Viewed 2536 times
First combustion cannon 006.jpg
Here is the igniter end of the tube and you see the positive and negative wires on each side of the poplar divider
First combustion cannon 006.jpg (19.5 KiB) Viewed 2536 times
First combustion cannon 007.jpg
Here's a view of the the entire thing
First combustion cannon 007.jpg (19.72 KiB) Viewed 2536 times
First combustion cannon 008.jpg
Here's my fuzzy attempt at an artistic shot
First combustion cannon 008.jpg (16.01 KiB) Viewed 2536 times
Ball valve attachment method.jpg
This shows how I attached the PVC ball valve to the ABS gun...
Ball valve attachment method.jpg (17.73 KiB) Viewed 2536 times
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Unread postAuthor: starman » Sun Oct 12, 2008 7:40 pm

Not a bad effort, especially for your first combustion!!

The chamber/electrical pod/propane tank "bunch-up" looks, well, like a bunch-up...missing a defined structure. The pressure gage looks like it isn't readable in the position it's in and the big ball valve air inlet in the rear is way overkill size wise.

However, my guess is that your shots are consistent and powerful if your meter is designed correctly. A longer barrel, maybe another foot or 2, no more for practicality reasons only, would offer another noticable performance increase.
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Last edited by starman on Mon Oct 13, 2008 1:47 am, edited 1 time in total.
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Unread postAuthor: Ragnarok » Sun Oct 12, 2008 8:44 pm

starman wrote:Not a bad effort, especially for your first combustion!!

Agreed, a sterling effort.

In fact, I would agree with all of Starman's points. The only thing I would personally add is it would probably benefit from slightly more ergonomic handles.
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Does that thing kinda look like a big cat to you?
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Unread postAuthor: ALIHISGREAT » Mon Oct 13, 2008 1:31 am

very nice indeed, although maybe you could have gone for a cheaper smaller ball valve :wink: but it looks very well made for a 1st combustion.
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Unread postAuthor: auxiliary » Mon Oct 13, 2008 7:33 am

Thanks for the quick responses!

Ya the ball valve was definitely overkill, but I had it laying around and it made for a comfy shoulder stock. I also didn't plan out the position of the propane tank and electrical pipe to well, but if I build a huge combustion (hopefully) I will take these things into account.
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Unread postAuthor: mark.f » Mon Oct 13, 2008 8:58 am

Looks very good! Although I have one suggestion:

3" SCH-40 (ABS, PVC, whathaveyou) make a great holder for propane tanks. If you were to integrate the propane tank holder and electronics holder into some 3" ABS, then clamp that on the side of the chamber, it would look better in my opinion.

Good job either way!
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