Posted: 07/09/2010 18:41 PM Post subject: selectable semi/full auto, non-electrical
Lieutenant Colonel
Joined: 05 Oct 2008 Posts: 416 787.14 Spud Bux
Hey guys so Ive been thinking about a mechanical way to achieve efficient full auto, I really like the reliability in the feeding and firing of the dcv and pneumatic cylinder type design. So I decided I would use that as the base, I know poland spud managed to do some full auto but I believe it used electronics and solenoid valves, which is great but I want a purely mechanical and pneumatic system.
I was thinking of trying to use some cam to selectively trigger my mead 3 way lever valve. But when I was looking through the bins at my local ReStore I found clippard 3way switch valve (50 cents) which I think will work even better, I will have a rod design (similar to tech's qdv rod) so when the pneumatic cylinder extends all the way after loading a bb it triggers this valve piloting the qev. The lack of pressure then makes cylinder retract, when it retracts all the way, after letting a bb fall in the breach it then pushes the valve the other way filling the chamber and starting the process over.
This will all be triggered by a blowgun feeding air into the system. To have selcetive fire I plan to have a way to bypass the rod, hold the blowgun trigger down, so I can trigger the switch manually with a spring loaded trigger, one shot per pull.
heres a vid of my test setup, I will use some elbows to reorintate every thing so the switch is in the right direction to be triggered by the cylinder.
it is possible to build a fully mechanical system, but it isn't as simple as you think.... the valve has to switch not only when the air cylinder extends but also switch back when it returns to the original position... it sounds more complicated than it really is - pic included for clarity
haha polandspud, thats exactly what Im trying to do with this design, the switch is bistable. But there are two contacts on the cylinders rod instead of the on the switch.
ohh ok... in theory it is simple but it will be a bit tricky to put everything together since both parts are usually attached to the opposite sides of the QEV
The pneumatic system is better in this respect and it is adjustable, but it requires an air piloted valve and a flow restricting valve...
On the other hand, the mechanical system will achieve the highest ROF possible.
The disadvantage is that it triggers the gun not when the max pressure is reached but when the air cylinder reaches a given position (but it don't think this will be a problem on a gun this size.... most likely the pressure will reach the maximum before the air cylinder extends fully (due to inertia))
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