SpudFiles

Hello all. So I'm Mimikool, a french member from the patator forum. I' could see some monsters in this forum and i'm happy to come with you.

I post here to present quickly my pneumatic cannons, and show you a new QDV design.

My first cannon, with a jack for the compressed air, and a simple QEV system no optimized at all. There is an hammer valve to strigger the shoot. I can shoot at différent caliber 6mm, 8, 12, 13.5 and soon 16mm for marbles. The service pressure is between 10 and 12bar (about 15psi)
The qev system will be replaced by the QDV that i'll speak about later.


Video :
[youtube][/youtube]


This winter, i'm builting a new cannon, more powerful:
The caliber of baril: internal diameter: 26mm and 28mm external.
The caliber of chamber : 26mm internal with 1" galva steel.
Baril lengt: 1m30.
Chamber lenght: 1m
Pressure : 150 psi for now, and 600maxi when i had my freege compressor.
Qev : 1" 1/2 tee, and a simple vavle for the exhaust.
Total lenght: 165cm

It miss le piston an the internal baril in the qev.

Pictures:




I've built a simple pen gun, for shoot bbs (pipes are glued with araldite (epoxy)):


Now i'll presnt you the QDV system, the theory say that the recul of piston is really fast but it hadn't a great acceleration, because a the begining juste a little bit of air can pass in front of the piston.

So i think this system witch give the acceleration that the piston don't have, when the projectil is light for exemple.



Both piston are in link, when we press the trigger, le right piston no longer sealing and the second toric seal, larger, do the sealing, so the diameter is larger at right than at left, le piston recul and after it's a tradditional QDV.

The difficult is the built problem, requieres that the piston is screwed in the other after that system is mounted.

I hope can install this system on my first cannon.

Thanks for reading !

Apologies my bad english, i try to don't use google translate because it give not very good things, and allows me to learn english too

Nice cannon. Shame about the sound. If you upload a video with out music Youtube will leave it alone then we can hear the cannon shooting.

Welcome to Spudfiles.

It's edited with the sound.

And when you reply, i felt the end of the post was not published...

So thanks !

To deal with the initial piston speed on the QDV, I used a short low mass piston and the trigger is not directly attached to the piston. This allows the trigger to gain considerable velocity before it contacts the piston. The piston then starts motion at a fairly high velocity. For lightweight projectiles, and dry fire, it has worked very well. Spliting open soda cans with marshmallows is trivial.

The long piston assembly and added length for the additional sholders and extra ring may add mass that will degrade the advantages of the steped piston.

Video of the tests are here;
http://www.youtube.com/user/Technician1002#p/u

Yes, i agree, the piston will be thin, in inoxydable steel, or aluminium. So it will be light enought i think. And thanks for the idea, i'll think to draw a simple design to make an independent trigger, with a slide may be.

But in this system, i wanted to deal with the initial piston speed with a pneumatic system, that give a constant power. I thought at springs but it's cumbersome.

It's my father who machining workpieces, and if that makes him less work, i think choosing your idea.

I found initial speed is not too much of a performance limiter. The pressure that moves the projectile also moves the piston. Regardless of the initial speed, the pressure that moves the projectile a couple times it's diameter also moves the piston a couple times it's diameter if the mass of both is close. Once things start to move, it does not stay slow for very far. Generally for apples, spuds, oranges and the like the valve fully opens before the projectile has moved it's own length. Lightweight projectiles such as marshmallows and empty pop cans tend to move a little farther, but still not far enough to have an adverse impact on overall performance.

Be sure the piston is low friction so the force works on the mass mostly instead of high friction.

For example here is what a fast valve can do with a lightweight projectile. This empty can was launched at a steel plate from a few feet away.

Ok, i didn't think the acceleration was so unimportant. I thought that's change considerably performances.

For the frictions, workpièces will be adjusted to a 0.01mm with the toric so the frictions will be minimized.

It's a good new for my father

J' aime bien ton QDV design mimikool! C'est trés cool et innovant!
I don't have as much experience with QDV's as Tech has (I think no one has.. ) but I think your Design could work well.

But I think I found a flaw: If the large O-Ring on the right is completely airtight, you will have a air cushion between the larger and the smaller O-ring while closing the valve, that will in the worst case prevent the valve from closing completely and lead to uncontrolled opening.
Or when closed and airtight, it will be hard to press the trigger because you are "sucking vacuum between the O-rings (you enlarge the volume there...).

But I think you could just leave the large O-ring not completely airtight, (or leave it completely if the piston is a tight fit) and your design could still work as proposed, the air loss would be very small me thinks...

Did you understand what I meant???

Or just go tech's proved way and reduce weight and friction to a minimum, but I personally am very interested in your own design!

Oh another thing! I think you can get rid of the left shoulder in the piston, because you have the right one, which prevents the piston to go too far, when it is closed. That would make it possible to machine the piston out of one piece, and could just inserted into the T from the rear, nothing has to be screwed together, if I understood your mounting problems right.

I speak a bit french as well, so don't bother to ask if you didn't understand something.

Oh Yes, i understood ! very good suggestion, for the shoulder, such it's simple, i'd never think. Thanks !

Yes, for the right piston, added at frictons, it will be difficult, mostly for 400psi. And with the machining center, i can have 0.02mm between the piston and the bore. The loss will be small in fact.

finely somone els who can desighn on graph paper.

you dont see manny of us lattely wonder what hapend
ah well at leasl it is easy to scale designs done on graph paper.
nice drawing live the micro pen gun been thinking about one but im preocupide with a m8ts demand.