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

Unread postAuthor: Leonard » Sat Aug 16, 2008 12:20 pm

Hey guys!

First of all, here's a link to the design i am currently making :

Image


I'v been working for the past months to achieve a semi/full-auto pneumatic 6mm launcher design that would not require any springs nor special tools. I have'nt posted a lot since after seven different protoypes, only one worked relatively well (http://www.spudfiles.com/forums/6mm-sem ... 15353.html)

But i am having surprisingly good results with the protoype in the making. Out of the whole design i have completed the upper and lower tube setup and the twin pistons (separated by a shaft). The reason why i have not finnished the whole thing (i am missing the bolt in front of the piston and the magazine, wich i am sure it will work as i have done it in the past) is because my main priority was to try this double piston and see how it works.

And it works! And much better that what i was expecting, in fact, i was able to go full auto by using a simple pop-off safety valve as the pilot and simply putting constant air flow into the chamber.

A few other details : the pop-off goes off at 110 PSI, the burst of air that is shot would feel like a sting if my hand is about 4 inch or closer to output of air. I am estimating 10 burst of air per second, but i would need to record it to be sure. Long story short : Satisfing design, at last. Coupling the piston with a loading bolt will result in a full auto 6mm launcher.

I'll probably be able to trow in a video and a few pics of the prototype if anyone is interested.

Before going through with the rest of the design, i need to rebuid the whole thing. The epoxy was not applied correcly at many places and some tweaking in the internals could have made the whole thing faster/more powerful.

I'll get back to you as soon as i go through significant progress.
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Last edited by Leonard on Fri Aug 29, 2008 12:22 pm, edited 1 time in total.
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Unread postAuthor: Mr.Sandman » Sat Aug 16, 2008 12:22 pm

what does ggdt say about velocity?
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Yeah, it's that important.
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Unread postAuthor: trollhameran » Sat Aug 16, 2008 12:31 pm

Do you have holes in the back piston to allow it to pilot quicker, or have you put the pilot in a different position on the actual gun?
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Unread postAuthor: al-xg » Sat Aug 16, 2008 2:02 pm

Ah good to see you got it working.
I would quite like to see a video :)
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Unread postAuthor: Leonard » Sat Aug 16, 2008 3:06 pm

I unfortunatly dont know how to use GGDT well enough to calculate the performance of this launcher.

There is no holes in the back piston, no springs behind it and the exhaust is exaclty like pictured. The piston dont seem to have any problem piloting (even with a slightly pressed blowgun) as there are 2 piston being pushed by 115 psi each.

I'll get a video of it tonight. Thanks for the comments.
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Unread postAuthor: trollhameran » Sun Aug 17, 2008 2:23 am

I just wondered if the pressurized space behind the second piston sloed down the piloting, but I suppose there is more force pushing back from the chamber side than there is pushing forward from the second piston.
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Unread postAuthor: jackssmirkingrevenge » Sun Aug 17, 2008 3:48 am

looking forward to seeing this completed, good luck ;)
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Unread postAuthor: the unit » Sun Aug 17, 2008 11:30 pm

the space between the pistons negates each other as there is equal force applied to both faces
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Unread postAuthor: Brian the brain » Mon Aug 18, 2008 10:45 am

looking forward to seeing this completed, good luck



Knowing the trouble you and I went though to try and build full auto mechanisms...that almost sounds sarcastic... :D
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Unread postAuthor: Leonard » Mon Aug 18, 2008 12:34 pm

the unit wrote:the space between the pistons negates each other as there is equal force applied to both faces


Hum... then i am a liar i guess!

No.

Actually, When Exhaust opens, the space between the left piston and the exhaust is exhausted. Then, the face on the inside of the piston negates each other BUT the right face of the right piston is pushed by air that is located in firing chamber. Firing is completed.

Then when the exhaust closes, the very small space between exhaust and the left face of the left piston quickly gets filled by incomming air leaking around the piston. The left face of the right piston gets pushes by the air trying to go through the firing chamber, sealing the chamber.

This design works. It uses a lot of air and need a pop-off valve, but it works.
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Unread postAuthor: Leonard » Fri Aug 22, 2008 3:28 pm

The prototype as been completely rebuilt from scratch, it now look a little better and is more compact than the previous one. Next step is building the bolt in front of the piston, wich i will work on next week.

I'll try to get a pic of the prototype and the double piston somewhere this weekend.
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Unread postAuthor: Sticky_Tape » Fri Aug 22, 2008 4:29 pm

How does the forward part of the piston seal the barrel or whatever?
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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
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Unread postAuthor: Leonard » Sat Aug 23, 2008 10:41 am

It does not seal the barrel, it seal a tube just slightly larger than the barrel in wich the bolt slide. The bolt is the same size as the barrel (and could have be en the actual barrel in wich the projectile travels) but it is cut and the remaining barrel is glued 3 centimeter away (i dind wanted a barrel that would move when shooting).
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Unread postAuthor: Leonard » Sun Aug 24, 2008 1:22 pm

Here they are :

Full view

Image

Fill and exhaust

Image

Canon-cover and firing chamber

Image

Inside chamber from exhaust

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Piston

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Piston again

Image


And a quick little video :

Image
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Unread postAuthor: elitesniper » Sun Aug 24, 2008 1:27 pm

You held it with your foot? :lol:, nice work with jb weld. :D
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