Yeah, "unfortunate" is one way of describing those prices lol! The gas one looked pretty impressive though, eh? I mean, yeah, the wind was behind it, but even so...
Anyway the principle is sound: the smoke generating fluid is heated to produce the effect.
Forget $70 aerosols, the
liquid comes in Litres for a fiver. You can get stuff that creates denser and/or more persistent smoke too for way less than $70. The trick then is to turn only as much as you need into smoke, on demand, and add it to the pressurised BB feed at some point...
I think pressurising it is the way forward. All we need is a gasketed seal on the reservoir's fill cap and a valve from the compressed gas/air tank. However controlling the outflow could be achieved in 2 ways: depend purely on the width of the out pipe and the restriction of a valve, or use a diaphragm regulator and valve, like those on red/blue propane/butane bottles, but the amount we would need to flow per second is something that could only be established by trial and error.
Another issue is that under
no circumstances can we have hot pressurised unvaporised smoke fluid coming out of the muzzle! I suggest that the vaporisation chamber needs to be a vertical tube heated from the bottom, with plenty of space above the heating element for expansion, but also with the outflow on the rear of the top, so that the wearer could still lie face down without any fluid being able to get out of the chamber. To counter any risk of fluid escape due to acrobatics (intentional or not), either a small coil, like on a still, would trap it and make it flow back into the chamber once vertical again, or a U-bend type trap after the vaporisation chamber should catch it, we'd just have to remember to clean it out if the unit got turned upside down or something similar.
Also it would be better if the smoke joined the BB's right at the muzzle, so it didn't flow through the same barrel/s as the BB's because it would almost certainly coat the inside with enough goo to cause feed problems.
As for the element itself, 1 or more dismantled car cigarette lighters and pretty much any AEG battery ought to do the trick.
Edit: A regulator would undoubtedly add an extra element of safety to the system, but it would also then require a a separate feed down to the muzzle, because the 2 systems would be at differing pressures then, and also the muzzle would need some kind of mix chamber to let the smoke and BB's out without pressure from the BB feed backing up the smoke. Something shaped like a simple jet engine ought to do it...
