There are some things about PCM radios you should know.
PCM uses Frequency Modulation to transmit its signal, so it is still susceptible to interference. The difference, though,
is that a standard analog FM radio will respond to any signal - good or bad. The result is the familiar “chatter”
the servos make as they wildly try to follow meaningless signals. If a PCM receiver gets a bad signal, it ignores it. It remembers
the last good signal it received and simply holds that servo position until it gets the next good signal. Normally that happens
within a fraction of a second. If you are making the usual smooth and gradual control inputs common to pattern flying, you
will never even know you had a “glitch”. The end result is that you can be getting slight interference with a
PCM radio and never know it. And, of course, this is both good and bad. Good because PCM appears to “burn through”
much of the interference you get with standard FM radios, so your pattern sequence stays glassy smooth. Bad because you have
a serious problem by the time you finally do notice it.
So, how do you know if you are getting interference with PCM? There are a couple ways. If the plane does not respond to
abrupt inputs - like a snap roll - exactly when you command it, you were likely “hit“. Also, if the plane does
not exit a maneuver - like a spin - when you command it, that is a another sign of a “hit”. In either event, land
and accomplish a range check on your radio.
Another feature unique to PCM is the “failsafe” function. This gives you the ability to select a specific position
for each servo to assume, should the receiver lose its signal for more than a second. Although you can set a position for
all the servos, you will not be able to save a plane with failsafe. We have taken great effort to make our pattern planes
aerodynamically neutral…so they will not fly by themselves like the old free-flight designs could. The failsafe feature
CAN enhance safety, though. A runaway 150cc engine at full throttle will chew through just about anything it hits. For safety
sake it makes sense to at least set the throttle failsafe to no more than idle. That small detail could save your, or someone
else’s, life one day.
PCM coding gives you 512, 1024, or 2048 precise points for positioning each servo, depending on the radio you choose. Of
course, the 2048 radios are new and very pricey right now, the 512 systems are dated, so the 1024 systems currently remain
the best value. A 1024 system gives you 1024 precise points of servo position. A normal servo turns 120 degrees from stop
to stop, so a 1024 radio gives you 120 degrees divided by 1024 steps, or .12 degrees per step. That is pretty accurate.