Polygon
How Drozd works
Drozd is a CO2 air gun – it mean that pellets accelerated by compressed CO2. In cylinder
CO2 stores in two phases – liquid and vapor. When a part of vapor phase exhausted for
shot, a part of liquid phase become vapor and pressure of vapor phase become very
constant, depending only of temperature. All it means, that ALL shots of CO2 gun have
equal power while CO2 cylinder contains liquid CO2. Count of equal shots is something from
55 to 90 per one 12 gram CO2 cylinder, depending of fire mode and temperature.
But CO2 pneumatic isn’t perfect – after each shot CO2 a bit cools down when vaporizing
and it’s pressure also become bit lower, until propellant’s temperature became equal
to temperature of environment. It results less power of each next shot when firing
rapidly. And, of course, a power of all CO2 guns heavy depended by temperature of
environment – at 30C vapor phase of CO2 have pressure of 75psi, at 20C – 55psi, at 5C
– only 35…
To make drozd fire bursts without heavy drop of shots power, designers install just above
CO2 cylinder a big pre-vaporizing chamber, that store vapor CO2 enough to power several
shots without intensive vaporizing liquid phase. With limitation of max burst length by
six, it results approximately equivalent power of all six shots.
Action of gun isn’t difficult. When the trigger pulled, chip-based square pulse
generator becomes producing short pulses of voltage opening a power MOSFET. MOSFET
connects two big capacitors charging directly from batteries to electromagnetic hammer
behind magazine slot. Hammer hits valve control pin installed into magazine top producing
doze of CO2. Top BB, stored in magazine, already positioned coaxial with barrel and CO2
pulls it forward. When the shot completed, next BB with power of spring comes to fire
position.
Boosting the fire rate
A construction of gun enables to boosts fire rate up to 900 RPM (15 shots per
second) with all drozd parts still works normal. To boost fire rate needed to do some easy
modifications with electronics. If you look at bottom side of PCB, you can see a 3 flat
resistors connected to pins of fire rate control switch. Using soldering iron add in
parallel a 50K resistor to resistor of middle switch pin (a switch position is 450 RPM).
It will result a 900 RPM fire rate, when drozd switched to “450”.
More materials will be added in future
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