gyro, there’s typically a menu step for adjusting
travel limits. The slider should stop a millimeter
or two short of the rotor hub at one end and
the shaft bearing at the other. A stalled servo
is going to get hot quickly, so make sure it’s
not just trying to travel too far. If your particular
helicopter doesn’t have this menu option,
you can adjust the travel endpoints on your
transmitter or simply move the ball link on the
servo arm to an inner hole. This is good practice
anyway; you should always use the innermost
hole on the servo arm that will still allow you a full
range of travel. With today’s sophisticated radios
and flybarless systems, it’s all too easy to forget
basic best practices.
If everything with your mechanical setup looks
right—no binding and slider travel not exceeding
its limits—it’s time to look at the electronics. The
first and easiest thing to check is the analog/
digital setting for the flybarless unit or tail gyro.
Running an analog servo with the stab unit
set to digital can cook the servo in seconds.
These days, with digital servos the norm for
helicopters, this is a less common mistake than
in the past, but just as Karl said in Sling Blade,
the first step is always to make sure the engine
has gas in it.
The next item to check is the tail-servo
frequency settings in the flybarless module.
Units like the popular BeastX MicroBeast have
menu settings for the tail servo’s pulse length
(usually 1520 or 760µsec) and servo frequency,
which can range from the default frame rate of
Many flybarless suppliers, like BeastX, maintain a database of recommended settings for all major makes and
models of servos. Al ways use the recommended pulse-length setting (typically 1520 or 760µsec), and never
exceed the recommended frequency. If a servo insists on running hot, try a lower frequency.
To check for binding in the control linkages, disconnect
the tail pushrod from the servo arm and slide the
pushrod back and forth manually. There should be
almost no friction. Remember that tail servos are
designed for speed, not for high torque, so even a little
excess friction is a bad thing.
50Hz all the way up to 560Hz for some servos.
Much like running an analog servo in digital
mode, selecting too high a servo frequency
can push the servo to the point of failure. Even
if you’re using the recommended settings for
your particular servo, you can always try a lower
frequency if the servo is running hot.
The final and most variable setting to check
is gain. For years, a widely accepted rule of
thumb has been to increase the gain setting
until the tail starts to wag and then to back
it off a few percent. The potential problem is