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Build log -- Full-auto 6mm - First Test Shots : FAILURE

Post questions and info about pneumatic (compressed gas) powered cannons here. This includes discussion about valves, pipe types, compressors, alternate gas setups, and anything else relevant.
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Unread postAuthor: Leonard » Mon Aug 25, 2008 4:17 pm

Thanks a lot for the comment guys, makes me feel that all that work was worth it.

Brian the brain wrote:And maybe maybe pay a little bit of attention to the look of the gun :D
T


The looks is realy not what interest's me. It's pretty easy to open up a toy gun and fit my prototype in it. It will look good, but it's not challenging nor inovative.

The gun is finnished and is in working order (shooting working order). Still a lot of tweaking needs to be done (and the ball stop) But it's working. I'll be sure to get videos and pics for you guys.

Also. Some have been comparing this to a QEV piloted by a pop-off. The result is similar, but the actual goal i had in this was to make a piston that would ALSO be the bolt, so only 1 moving part. A bolt could not be attach to the diaphram of a QEV, so a blow-forward mecanism would be necessary.

To answer some questions : The power of this prototype is surely greater than any battery powered BBMG, but the use of air is pretty high. I call it "inverted spool valve" as it is, in some way, a spool valve but piloted from the back. It is more simple (and it get rid of the need for a o-ring under sheer/compression duty) BUT, it is also more air hungry.

Finally, feel free to duplicate this idea and make it better. My goal was to design somethign efficient and easy to build with a minimum of tools, but if someone who has access to a lathe and other stuff like that, he could surely reproduce and make it better!

Thanks again, i'll get some vids for tommorow.
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Unread postAuthor: Leonard » Fri Aug 29, 2008 12:55 pm

Yup, that's right, it failed.

The finnished launcher as been laying around for a few until i could go out i do some test shots. Today was this day, i packed everything up and walked out of the city (i live downtown in a one room appartement :shock: ) into the wilderness to try it out.

Here's a pic of the finnished piston/bolt :
Image
Open Position :
Image
Closed Position :
Image

Oh! I almost forgot. I have made semi-auto shooting tests a few days ago, i worked pretty well, no ammo going out at the end as there was no more in the magazine, but it was a promising test, here's the video :
Image

So, with the positive results i had, i was pretty confident in the full-auto test i did today. I adjusted the reg to 125 psi and try some blank shots. The darn piston/bolt would not actuate. I greesed it a little, tryed again, it did actuated but the power was terrible. I figured something awful :

The bolt created too much friction to be piloted by a pop-off valve.

To solve this problem, i tried using a little more pressure, around 155 psi. Magic! The piston cycled pretty well at this pressure! I only did a few bursts to save air and i filled up the magazine for some real shooting...

I turned on the camera, stood in front of the cola cans and started shooting. BAM! The bolt ripped itself appart from the piston and went crash into paint can, the piston's sealing face broke off, the magazine went flying into the air, spreading the BBs around. I picked up the bolt on the ground.

Hours of sanding and polishing was to be trown to the garbage, the bolt is now useless.

I opened up the launcher (this is where i realised the epoxyed sealing face got ripped of) BUT the twin piston were intact! For the fun, i glued the sealing face back and tried blank shooting bursts of air, everything worked perfecly fine! (without the bolt, there was very few friction, so the piston would actuate easily).

Lesson learnt, this design is pretty awesome in theory, but darn hard to make without machining parts. It DOES work (and is more powerfull that a blow-forward bolt) on semi-auto with a reasonably efficient pilot (Ball valve). But for full auto, it needs a bolt without friction, a very sturdy one piece bolt/piston and a spring loaded magazine.

Good luck to the ones who will possibly duplicate this, i'd be very happy to see someone make this design work.

Next step : combining the full auto twin piston with a perfecly made blow-forward bolt.
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Unread postAuthor: Brian the brain » Fri Aug 29, 2008 4:02 pm

So you have stumbled upon the age old dilemma.
It nearly broke me and JSR.
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Unread postAuthor: jackssmirkingrevenge » Sat Aug 30, 2008 2:46 am

Brian the brain wrote:It nearly broke me and JSR.


Indeed, the Fullauto Club looks something like this:

Image

:?

Perseverance is the key however. The theory is sound, all you need is the will to follow it through and make it work. On that note, Brian seems on the verge of achieving success, looking forward to some decent performance :)
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Unread postAuthor: daberno123 » Sat Aug 30, 2008 8:43 am

Hopefully you did nothing to cause the sirens in the beginning of the vid... :wink:

It's really to bad that this didn't work, It was a design that I thought had some true potential. JSR summed it up, just persevere and success will come. Good luck!
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Unread postAuthor: Leonard » Sat Aug 30, 2008 12:58 pm

daberno123 wrote:Hopefully you did nothing to cause the sirens in the beginning of the vid... :wink:


Haha! i live downtown city, so siren sound is becomming a constant background music...

Thanks for the comments. Im sure that this design could work, it just need to be made REALY well. Im ordering more brass tubing and other materials wich will let me build a piston/bolt that would be just one piece, so no risk that it would break again. i also need a 1/4" ball valve to bleed the air slower into the chamber to get a lower ROF (So that a normal spring loaded tube magazine can keep up with the ROF). And get good grease and a lighter piston.

I feel a little discouraged by this failure, but i might try my luck at another prototype sometime soon ^_^
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Unread postAuthor: Sticky_Tape » Sat Aug 30, 2008 3:15 pm

You do know that there are special flow valves that regulate flow right? I think they are called needle valves.
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You can tell how awesome a cannon is by the pressure used.
http://www.spudfiles.com/forums/high-pr ... 12803.html
xnt rnm ne z ahtbg
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