New Project: Wire-Controlled Air Burst Cannon

[SEAKING9006]

UPDATE July 24: Cannon complete. Please see the thread on the CA3 PDAB, the completed version.




My next project will be a launcher that fires a round containing flour packed into a clamshell inside a 1-piece sabot. The sabot is attached by a spool of pre-cut high-load fishing line on the rear of the launcher, housed in a small piece of PVC at the rear of the breach. The ammo will be a plastic bottle 1-piece sabot, with a two piece clamshell, made from a soda can. there will be about 6" to 1' of twine attached to the inside of both the clamshell and the sabot. Inside of that, will be loose-packed flour. Future designs will incorporate a trigger mechanism to allow for controlled bursting. This design concept is mostly intended to increase my skills in working with modified fittings and making multi-part ammo. I will begin working on the prototype as soon as I get the fittings I need. On a side note, the tank will probably end up being two sections of 2" on a tee, due to a lack of access to pressure rated fittings above 2".


I have added the third revision of the concept drawing. There is no longer a vulnerable breach hole for the line.

EDIT July 1: The first prototype should be operational by the 17th, depending on when I receive the proper fittings. The design has been finalized and is in the production queue.


EDIT July 22: I will be going to Home Depot today, and I will get all of the necessary fittings and pipe to build this thing. I got a sack of flour yesterday, and the bottles are air-drying as we speak. Gun should be complete in three days, and firing by the end of the week.

[pizlo]

It either won't burst until impact, or it will burst right as it leaves the barrel.
Well maybe not, but thats what seems reasonable. Even if it only burst on impact it will still be cool. And realy its just for experience so you can't lose.

[SEAKING9006]

Well, it's not meant to impact. It's meant to fly out until the wire runs out, pull taught, and the front part of the shell keeps going for about a foot, thanks to the inertia of the flour. The main sabot keeps it together until then, as it's nothing more than a cup.

[MaxuS the 2nd]

The clamshell will need to be packed tight enough to not just fall out, but loose enough that when the sabot reaches the end of it's teather, then the shock will force it out.
What happens when you want to fire another shot?
Do you reel it back in and reload?
Would be a bit of a bitch to reel it back in over rough terrain.

[SEAKING9006]

No, it won't be reeled in. The breech (either a union or a threaded plug) will be removed. The entire reel assembly is removable. You just pick up another round/reel, slip the sabot into the breech, close the breech, and pressurize the tank. It will be cumbersome, but it's not meant to be used as a combat weapon is airsoft or something. THAT launcher will come later.

[jrrdw]

I don't think you will be able to stop the air leak where the string enters the pilot chamber. Air leaks in pilot chambers can cause a miss fires.

I would mount the spool of string/thin wire underneath the mussel and feed the atched down the barrel on top off the loaded ammo. Might yank when the slack takes up out of the string, but if your broad casting your ammo, that might make the yank a plus, I don't know.

[SEAKING9006]

It won't leak, because the valve isn't there. That's not the pilot. That's the breach.

[MaxuS the 2nd]

The Tee gives the impression of a piston valve. I think that's what Jrrdw is referring to.

[SEAKING9006]

Yeah, me too. It's just a tee so I can mount the reel assembly behind the breach.

[jrrdw]

Ok, I want to see what valve your going to use. Are we to understand that the main/firing valve is placed below the tee?

[SEAKING9006]

Most likely a modded sprinkler. And yes. That a bad thing?

[MaxuS the 2nd]

I'd agree with Jrrdw on this one. If you mount the reel underneath the muzzle then it'll both be easier to reload and also the pressurised gas won't vent out the back through the string hole instead of down the barrel.

You will also need to account for the amount of friction. There will be more friction on the twine if it were coming through the back rather than be set underneath the muzzle.

Thats how the pro's do it.
http://www.antennalaunchers.com/csv19/index.html

[SEAKING9006]

I was planning to reduce friction by rounding the edges of the hole. Also, I placed it behind the breech to avoid the -yank- that occurs on types with muzzle mounted spools. If that happened with this ammo, it could cause it to burst early. And also to reduce friction, I was planning on using heavy fishing line.

[D_Hall]

Your string is going to break. As the projectile begins to move forward the string will pull taught. The inertia of the reel trying to spin up will be too much for the string. SNAP.

How to fix?

Don't use a reel. Use a spool. Set it up such that the string is pulled off the top of the spool (so that the spool doesn't have to spin to let string out).

You may still find yourself snapping strings though.

Best bet? Incorporate the spool into the projectile; not into the gun.

[SEAKING9006]

How's that going to happen? As long as I use strong enough fishing line, it should work.