Semi Auto Nerf Gun

Ragnarok · Tue Oct 28, 2008 11:04 am

judgment_arms wrote:there goes efficiency and ROF will be limited

Not at all. I would reckon given that it's using energy that's left over after the dart is already gone, there's no efficiency loss at all. Dropping the chamber volume by the amount the cylinder adds is all you need.

ROF is also peachy, as it starts reloading as the chamber empties, and is fully reloaded before the chamber's even full again. To me, that says it's no slower than the rate at which the chamber is cycled, and in that sense, is not a limiting factor in ROF.

there's a lot of timing to get this thing singing

Not really - as long as the return force on the cylinder is in the right sort of region, that's all it needs.
It will handle it's own timing after that.

by the way, is the new LRC done yet?

Actually...

...No.

Lentamentalisk · Tue Oct 28, 2008 3:19 pm

from what I understand, there is no "extra volume" that needs to be dumped. That "extra volume" is actually the chamber, and as long as you have the ratios right, should waste next to nothing.

judgment_arms · Tue Oct 28, 2008 8:34 pm

Lentamentalisk wrote:from what I understand, there is no "extra volume" that needs to be dumped. That "extra volume" is actually the chamber, and as long as you have the ratios right, should waste next to nothing.

what I'm getting at is, the valve does not need to stay open the entire time the projectile is in the barrel.
there's a cut off point, a proverbial "windmill" or point of no return, were once the projectile has passed this point any excess gas will not be used efficiently or not at all.

if the valve closes or the dump chamber empties at the ideal time, there will still be pressure in the barrel.
the breach will either not open, or open to soon.

POLAND_SPUD · Wed Oct 29, 2008 12:33 am

the breach will either not open, or open to soon

I am more than sure that inertia will do the job...

judgment_arms · Wed Oct 29, 2008 11:10 am

POLAND_SPUD wrote:
the breach will either not open, or open to soon
I am more than sure that inertia will do the job...

what inertia?
we are talking about a FASOR ram, or Forward Air Spring Operated Return, correct?
there are forces acting on both sides of the ram; the spring pushing it back, and the air pushing if forward.
as the ram moves back towards the air source the volume decreases and pressure increases, slowing down the ram and eventually stopping it.

if the dump chamber empties (which would be required for the gun to cycle) before projectile leaves the barrel, there will still be pressure in the barrel, and there will be blow-by up out the magazine: wasted gas and potential feeding issues.

if the valve closes before dump chamber empties (as it should for proper efficiency and to eliminate blow-by): the ram will not move, or not go all the way back.

Ragnarok · Wed Oct 29, 2008 12:44 pm

judgment_arms wrote:if the valve closes before dump chamber empties (as it should for proper efficiency and to eliminate blow-by)

I seriously doubt most, or for that matter, any of us fiddle with our piloting mechs so that they pinch the QEV shut the instant the projectile is gone.
It's a whole kettle of fish that adds extra complication. Trying to stop your chamber cycling to zero after firing is a waste of effort, IMO.

As such, the pressure falls to zero, and the ram cycles. Given that this runs off that spare air, it's much more air efficent than any other air-operated loader design I can think of. Blowback, blow forward, gas operated - they all waste air and harm power in much great quantities that this will.

I'm not saying I haven't considered similar ideas - indeed, it would halve air usage on something like HEAL - but HEAL's piston valve is designed to open quickly and dump huge amounts of air - trying to close it quickly would be hard and fast destroy it.

judgment_arms · Wed Oct 29, 2008 1:43 pm

yeah, I'm starting to think that I'm stressing the milliseconds just a bit to much...
but efficiency is only half my point, the blow-by generated by the bolt opening as the valve is draining the dump chamber could cause feeding problems, particularly with gravity feed of light projectiles, I.E. paintballs.

Ragnarok · Wed Oct 29, 2008 1:56 pm

judgment_arms wrote:the blow-by generated by the bolt opening as the valve is draining the dump chamber could cause feeding problems

The prevalence of that effect can be countered by design.

Air dumps fast. Some kind of damping, or extra mass in the bolt system (perhaps a bolt that's a little longer than it has to be could be an option) could slow the reload enough to allow a full air dump.
It might need tuning to get the best ROF and reliability combination, but all you'd need to do is increase that delay or damping until the reliability was all pukka, then just leave it at that.

judgment_arms · Wed Oct 29, 2008 2:05 pm

on that note, why not use a flow control valve between the dump chamber and the ram?

high flow = quicker cyclic rate
low flow = slower cyclic rate

Ragnarok · Wed Oct 29, 2008 2:18 pm

judgment_arms wrote:on that note, why not use a flow control valve between the dump chamber and the ram?

Mostly because the chamber is the ram on this design. Although, that is something I have considered for 3vo, to try and get the adjustments right.

judgment_arms · Wed Oct 29, 2008 2:29 pm

Ragnarok wrote: Mostly because the chamber is the ram on this design.

yeah, I kind of forgot the original post...

PVC Arsenal 17 · Mon Nov 03, 2008 7:06 pm

Oh sh*t I haven't been on here in a while!

Well there isn't a whole lot of progress on my gun. That's mainly because I'm thinking that the cylinder-above-barrel design is too inefficient/diffucult to build. The main problem with it is that the piston-bolt connection will be difficult to make strong, and would require an additional groove cut into the barrel. Since air was to flow through the bolt, it's also an air restriction.

I'm trying to figure out the best way to set the cylinder inline with the barrel. That seems to be the easiest, strongest way to build the moving parts of the gun. The problem I'm facing with that though is where and how to channel the air into the barrel for firing.

I started to build the gun with the inline configuration and I'm almost finished with the breech opening.

Here are some pics/videos:

http://s237.photobucket.com/albums/ff15 ... IM0762.flv

http://s237.photobucket.com/albums/ff15 ... IM0763.flv

In the first video, bolt seems to be retracting slow- it is. I was trying to work the slide check with only one finger and I wasn't able to close it completely. The cylinder can actually extend and retract extremely fast, especially with a QEV.

VH_man · Mon Nov 03, 2008 7:13 pm

Very Sweet. I have actually Used your Design in a paintball gun. It works AMAZINGLY. Not in a state where i want to post it though.

Congrats on making a simple method of Semi-Auto.

PVC Arsenal 17 · Mon Nov 03, 2008 7:16 pm

Nice! But I can't take credit for this design. I may have thought of it on my own but I wasn't the first one!

VH_man · Mon Nov 03, 2008 7:22 pm

Whatever.

And i like the Inline design. Looks quite effective.

As for a method of getting the air in, Do what people do for Airguns and Just drill a hole that lines up with the rear of the projectile when the breech is closed. Get your QEV to blow air throgh that hole to fire. You could even set this whole thing up to be EXTREMELY compact....