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B2TB: sawed-off 35 bar repeater

Built a pneumatic 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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Unread postAuthor: Zippster » Mon Dec 08, 2008 11:00 pm

Yes its a necro-post, and I'm sorry, but I had to ask:

How did you modify the QEV to fill from the chamber? I'm looking into a similar firing mechanism like this and I just can't get how it keeps refilling the pilot. I've got a 3/4" QEV with a rubber disk as a piston kind of like a diaphragm which I doubt is moddable, but its still worth a shot asking.
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Unread postAuthor: Lentamentalisk » Mon Dec 08, 2008 11:04 pm

just open it up, and punch a SMALL hole in the diaphragm/piston thing near the edge, in the part between the pilot and the chamber (NOT BETWEEN THE PILOT AND THE BARREL!), and add a very light spring behind the piston, so that it is normally closed.
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Unread postAuthor: Brian the brain » Tue Dec 09, 2008 4:00 pm

Thank you.
It's that simple.

I wonder when we'll start seeing this idea in other peoples launchers...


It's taking you guys a while to get with it...


It reseats with a blowgun as the pilot valve as well you know...
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Unread postAuthor: Zippster » Thu Dec 11, 2008 12:52 am

Wow. I tried the QEV mod just a moment ago and for once something actually works. Thanks for that one, but theres one more piece to the puzzle - the pilot. What did you use to pilot this beast?

Lastly, does the time spent open for the valve affect the power of the shot? That is, to get more power, should one design a pilot that reseats slower to use more air and vice versa, or am I way off?

PS: And at 35 BAR, how strong of a hammer do you use to pilot the thing?
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Unread postAuthor: Brian the brain » Fri Dec 12, 2008 2:31 pm

You answered your own question: hammer valve

I needed a brass ( heavy)hammer and a pretty strong spring to speed it up.The last bit comes down to just mementum, the spring can;t keep pushing the hammer valve open, so the last bit of hammer swing is not powered by the spring if you get what I mean.

Longer opening of the pilot dumps more gas into the barrel.That is obvious.
But you don't need that much time because after a split second the ammo is out and you are just wasting power.

Imagine your ammo reaching 200 m/s.
That means an average of 100 m/s ( from 0 to 200)
If your barrel is 1 meter long, it will take 1/100th of a second for the ammo to leave.
that's still just 10 milliseconds.
Add another 10 for the valve reaction time ( overestimation!!) and you'd be safe to say you only need a short tap.
If your good with a blowgun you could still get repeatative shots without the effort of building a hammer and hammer valve.


Great news you tried it!!
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Unread postAuthor: psycix » Fri Dec 12, 2008 6:10 pm

Hehe...
Eindelijk iemand overgehaald zen QEV te modden :D
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Re: B2TB: sawed-off 35 bar repeater

Unread postAuthor: air soft fan » Thu Sep 08, 2016 2:54 pm

jongens, It looks great, works great meaby it is just great. Man BTB way are you so damm good in this stuf.
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Re: B2TB: sawed-off 35 bar repeater

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Re: B2TB: sawed-off 35 bar repeater

Unread postAuthor: Brian the brain » Thu Sep 22, 2016 12:29 pm

Without this forum I'd never gotten this far. We all feed off each other. But thanks...you have seen this one right?
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