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My First Coax Cannon

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 First Coax Cannon

Unread postAuthor: Mountain Storm » Fri Oct 29, 2010 9:40 am

4" x 24" chamber, 2" x 48" barrel, electronic ignition. Still Spray and Pray, but I can see modifying this one for compressed gases.

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One thing I plan to change pretty soon is the way the chamber seals up and the way the bore is recessed into the chamber. Makes loading a spud a right PITA. But for other projectiles it's perfect as is.

Other projectiles?

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I've got some destructo tests planned against jugs, sheet metal, OSB, etc. Just need to find a bit of play time.

The 6-32 bolts that form the spark gap are sealed with rubber washers, metal washers and nuts from the inside. They come into direct contact with the igniter so no wires at all on this one. Handle comes off from the outside (double nutted bolts on the chamber) and the ignitor fits into the handle with no modifications.

Like I mentioned I want to improved the breach loading action and I think the way to go is to make a short section of 4" with a permanent cap on one end and a female thread to solvent weld on the the other then extend the bore with a coupling and that would have the bore stick out of the chamber to aid the insertion of a spud.

I have more handle ideas percolating, just need to find some "me" time to get into them.

The thing needs a sight on it too, now that I have some projectiles that fly true I can start dialing it in.

The bell reducer on the front has been filled with epoxy after the 2" pipe was slipped through and glued into place to eliminate that possible weak spot. I used West System epoxy mixed with colloidal silica and filled the entire "funnel" shape.

In the chamber I used by blocks stuck on with foam tape to stabilize the bore.

A fan or other way of purging the chamber would be nice, but space is pretty tight.
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Unread postAuthor: Crna Legija » Fri Oct 29, 2010 9:58 am

shame you didn't go with a meter, otherwise pretty good. gonna paint it?
try get a pc fan in there to mix the fuel better.
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Unread postAuthor: Technician1002 » Fri Oct 29, 2010 10:28 am

One of the problems with coaxial spray and pray with smaller diameter chambers is the close proximity of chamber components to the combustion gases. This large surface area of both the chamber wall and the barrel provides a large close surface for the heat of combustion to escape to causing rapid cooling of the combustion gas and resulting loss of power.

For Coaxial combustions, I highly recommend as large a diameter as possible so most of the combustion gas is not adjacent to a cooling surface.

Modifying for compressed air use is recommended. Radiant cooling is not an issue. Radiant heating during the cooling due to expansion works in your favor, not against it.

Even my very small Mouse Musket was a great performer.
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Unread postAuthor: Mountain Storm » Fri Oct 29, 2010 10:29 am

Meter? As in pressure gauge? Not sure about paint. Paint usually gets damaged and looks like crap in short order.

My intuition was that the chamber shape is far from ideal for combustion, but for $25 in parts I'm not complaining. I'm sure I'll move on to bigger and bigger cannons...but I'm still impressed with the power of this one versus the 1.5" x 3" I built before.

Seems like having the combustion chamber as one section and breach and bore as another would be the way to go. Still thinking about ways to do that without spending a bunch of money.

I took a few vids of it in action. I started off with spuds but soon migrated to wooden projectiles.

[youtube]http://www.youtube.com/watch?v=VtaAxtRs22s[/youtube]

[youtube]http://www.youtube.com/watch?v=SMtAn1JEsAU[/youtube]
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Unread postAuthor: Mountain Storm » Mon Nov 01, 2010 9:44 pm

A little update. I've shot all manner of things out of the cannon. Even potatoes. It's been reliable. And it has a satisfying amount of recoil :twisted:

My favorite so far is an improvised cardboard shot shell full of mini marshmallows straight up. But busting jugs is fun too.

[youtube]http://www.youtube.com/watch?v=6X3ZCYe4K64[/youtube]

Here's one one that's the Breakfast of Champions. Carbs Kill
[youtube]http://www.youtube.com/watch?v=vQnJldApXvU[/youtube]

And it can send them pretty far down range. This one is a wood potato with a tail fin.
[youtube]http://www.youtube.com/watch?v=-R0e7PZ9qLs[/youtube]

Latest development is a "proper" igniter grip. I just slammed one together after dinner so it's not pretty, but it does the job.

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Once I get it looking a bit more pro I'll start a thread on it.
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Unread postAuthor: jackssmirkingrevenge » Mon Nov 01, 2010 11:12 pm

Love the half-arsed "yay" when you hit the jug :D

You really should consider moving to propane injection, chamber fans etc. though if you want to get the most of your combustions - the benefits in power and reliability will be evident.

Those are my two euro cents, however it's still a great job and your ignition/grip has a certain je ne sais quoi, I like it, especially with the exposed coil :)
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Unread postAuthor: Gun Freak » Tue Nov 02, 2010 9:59 am

I like this cannon, but I think you should put some propane metering on it. Like the grip too, nice job overall. I'm thinking about making a little combustion like this :D Maybe a scaled down version with a smaller barrel.
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Unread postAuthor: Crna Legija » Tue Nov 02, 2010 8:14 pm

Mountain Storm wrote:Meter? As in pressure gauge? Not sure about paint. Paint usually gets damaged and looks like crap in short order.


i meant a propane/mapp meter to get the perfect amount of fuel in the chamber, to would increase power and reliability
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Unread postAuthor: Mountain Storm » Tue Nov 02, 2010 9:58 pm

Gotcha. Metering is on the agenda.

Thanks for the comments :)

Another super hectic day. No school. 2 Kids full of energy. Sinus Cold. Many chores. Oh yeah.

But from about 7:30 to 9:30 tonight I managed to tinker a bit. The usual disclaimer that this is not pretty...but it does work.

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Addressed the main issues: fore stock, shoulder butt, sight.

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I felt circumscribed without a fore stock.

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Something to latch onto besides the barrel.

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That's some pretty trick joinery there mating the oak to the bevel. And the strap was no piece of cake either...but I got it right the first time amazingly enough.

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Not my best work. I went a little too far with the router and had to fudge the brace. But it works.

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The igniter seemed a bit vulnerable to damage so I used some polycarb and made a shield that also gives the shoulder butt some place to mount. Right now it's taped, but I'll screw it on when I take the thing apart to finish it up.

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Once I had the furniture attached I could see where to put a scope. I just cut a piece of 1" bar down to make my own beveled surface to clamp the sight.

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A little file work got it to clamp up securely enough. Then I used a longer piece of bar and drilled and tapped to mate the two. Then I used to 1/4" strips of foam tape to stick it to the cannon. It sticks pretty damn good. I was surprised.

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The butt stock will help me control the thing...recoil is pretty strong.

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After I play with it for a while tomorrow I'll take it all apart and see what I can do to make it a little better looking, sand it, treat it with linseed oil etc.

Fun part was I had all the stuff in the shop so no running around spending money to make it happen. The one thing I do want to buy is a single cell AA holder from Radio Shack so the battery can go in the control module. The modded controller was a good start, but it takes up too much room for no reason.

I'm also thinking about how to make a little nicer pistol grip with the switch hidden inside and a proper trigger.
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Unread postAuthor: Mountain Storm » Mon Dec 13, 2010 2:07 pm

[youtube]http://www.youtube.com/watch?v=msIQ0zPLaww[/youtube]

Little update. Using Tangerines :)

Tidied up the grip igniter assembly. Still working great several hundred shots later.
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Unread postAuthor: jackssmirkingrevenge » Mon Dec 13, 2010 2:15 pm

Nice :) like the way you've tidied it up.

Again you should consider moving up from spray-and-pray, all you need is a propane burner and a large syringe and you're good to go, you will be impressed by the power difference.

One small gripe - as with basic firearm safety rules, you should never let the muzzle cover anything you are not willing to destroy, in that regard your vehicle is not in the best of places.
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Unread postAuthor: Mountain Storm » Mon Dec 13, 2010 2:24 pm

I thought citrus was good for removing tar and bugs from automotive paint?

Yep Propane is on the list. After Christmas though.
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Unread postAuthor: Technician1002 » Mon Dec 13, 2010 8:04 pm

Nice shot. Too bad it wasn't ready in time for the best shot contest. The video could only be improved by using a good cameraman instead of running solo. Loved the sound of the shot. If you know the distance to the treehouse, you could do a rough audio chrony calculation on the sound.
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Unread postAuthor: Mountain Storm » Tue Dec 14, 2010 9:21 am

Thanks for that tip. I agree a tripod or a someone on the cam would be a great improvement. I'm trying to come up with a target that will maximize the effect of a tangerine exploding. Something messy.

Can you get any useful data from hang time on a vertical shot? Yesterday we launched one right through a low hanging cloud (I live on a mountain) and it took a surprisingly long time to reappear on the way down :D
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