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Micro repeater success

Built a miniature 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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Micro repeater success

Unread postAuthor: inonickname » Mon Apr 06, 2009 4:09 am

The goal?
To produce a small scale, high pressure cannon to rival the pengun series.

The twist?
Supply similar power, but with a 5+ round capacity!

Well after a lot of tinkering, blood, sweat and tears it's complete!

Construction is stainless steel, brass and epoxy with small amounts of plastic, spring steel and aluminum. On this scale, the most feasible way to give five consecutive shots was to use a hammer valve. And what better pre-made, low flow hammer valve that is cheap and available anywhere than the schrader? That said, it needs extensive modification..

The first adaption was to use a saw to cut down the top part of the valve, just above where the inside threads start then to smooth it off. At this point it's worth mentioning the variety of core I used. It's the longer type that has a long exterior spring. Easy to cut down, modify whatever..I completely cut it off. High pressure air easily closes the port.

Last of all, the part which is hardest to explain without photos.. the schrader was made to port directly up, rather than waste the tiny volume of air re-cocking the hammer.

The hammer is a stainless steel shaft, with a smooth plastic outer to reduce friction. The spring is simply a pen spring..nothing more to it. It's fairly soft, allowing for multiple shots.

On to the first test. The compressor was turned on (shock pump is broken, should get a new one..) and the chamber was filled to 70 psi and left for 20 minutes with not even 1 psi of leakage. Then the chamber was pressurized to 100 psi and the hammer actuated. It gave 6-7 full power shots then the power began to ebb away, eventually the pressure could not close the port and it leaked out slowly.

There's no barrel on it yet as I still need to make the persplex elbow (gah, why don't they make elbows in 3mm?)

If all goes well it will be encased in an epoxy stock then used with my (soon to get a new one-broken) shock pump for 400 psi shots.

As JSR would say, watch this space.

Image
Mechanism..Left-fill valve, right- hammer re-cocking mechanism. The brass bushing in the middle houses the modified schrader and porting.

Image
Mechanism and barrel, with Clide's cardapult for scale.

Future upgrades will include a trigger/sear, full automatic, a magazine, sights, a stock..the works.

Edit: gah..only just realized the pictures aren't to great. I'll do the barrel then shoot some with the canon.

Edit2: I just had a thought, flip the barrel towards the hammer end and use the hammer lever similar to a pump action or keep a traditional trigger/sear setup and face the barrel towards the fill valve?
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 06, 2009 6:23 am

Very interesting. It would be cool to see what sort of power you get from such a setup.

Actually, I never tried my schrader hammer valve with a barrel attached to see what sort of power it could provide, was too fixated on getting good auto cycling to care. I'll give it a shot when I'm home. It might have failed as a full auto valve but I see the appeal of making a small semi.

Looking good, hope it works out :)

Future upgrades will include a trigger/sear, full automatic, a magazine, sights, a stock..the works.


So it's not going to fit into a pen then :roll: how did you plan on achieving full auto? And why not a piston grip instead of a stock?
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Unread postAuthor: inonickname » Mon Apr 06, 2009 6:54 am

jackssmirkingrevenge wrote:And why not a piston grip instead of a stock?


:roll:

I guess it hardly matters. Anything I put in there that's even close to scale will be unusable for it's purpose.

I hooked up a short barrel and it will put sections of steel shaft through thin cardboard (that's at 70 psi, 70 psi is rubbish..), velocity/power seems to be close to my pengun of the same bore. No doubts 400+ psi will give enough power..If the design were to be reinforced unregged CO2 is an option 8) .

At the moment, without streamlining it more it would fit within the standard marker. Given it's not co-axial, it would be hard to pass off as a pen..

Full automatic probably wont be done, you wont even get half a second of firing like that. Plus with this much size to work with it would be hard to adjust the cyclic rate to a usable level. A lot of power would also be wasted re-cocking the bolt, whereas with this design it uses no energy re-cocking, just vents it all to the barrel.

I'm going to buy a new shock pump while we're in Albany for Easter holidays.

The power may not match that of the pen gun, but 5 shots at only slightly decreased velocity is nice. I'll get a video tomorrow..I just hope the format my cheap camera uses wont be rejected by YT.
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Unread postAuthor: spudtyrrant » Mon Apr 06, 2009 7:10 am

b-e-a-utiful that is the coolest thing i have seen since jsm's full auto. its one thing to make a simple gun of that size but to make a repeater that is truly astounding :P
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Unread postAuthor: jackssmirkingrevenge » Mon Apr 06, 2009 8:24 am

I'll give mine a go with 400 psi and 3mm BBs to see how it compares to the pengun and get back to you ;)

edit: tried it out and no contest. The pen gun goes through both sides of a pellet tin, the hammer valve won't even dent one side. I'm guessing it would have to be a closed system like in commercial airguns as too much air is wasted pushing the hammer back.
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Unread postAuthor: clide » Tue Apr 07, 2009 9:24 pm

That's really cool. I'm looking forward to the video.
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<a href="http://gbcannon.com" target="_blank"><img src="http://gbcannon.com/pics/misc/pixel.png" border="0"></a>latest update - debut of the cardapult

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Unread postAuthor: inonickname » Tue Apr 07, 2009 10:22 pm

Here's a movie (very dark..crud camera) of the mechanism unloaded. note the gauge in the background (small length of black tube is making up part of the chamber, that's why it got so many shots..Still gets several disconnected though).

Edit: d'oh

[youtube]http://www.youtube.com/watch?v=Wy6uZcNHGTg[/youtube]

Power is alright at 110, though it's nothing amazing. 400 will no doubt yield better results.

No sound either. Worlds crappiest camera.

Edit: Didn't use persplex for the elbow, just decided to make it out of delrin. Easier to work and stronger to boot. Hopefully I can get a video with the good camera (canon) firing some shots off before we go up to Albany. (down).

Anyways, 400+ psi coming soon
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