©2010 Skookum Robotics, Ltd
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20 Trouble Shooting Guide
Symptom
Problem & Solution
The SK720 stays in initialization
mode (LED stays red, won’t go
green).
The heli must be stationary and not
vibrating for the unit to initialize. This
symptom can also be caused by large
amounts of electrical noise.
Helicopter tends to drift (feel
loose) in elevator and/or aileron.
Hiller gain is too low.
Hiller gain isn’t high enough, even
at 100%.
Increase cyclic blade-pitch range
After a sharp elevator or aileron
command is released, the
helicopter oscillates slowly.
Hiller gain is too high.
While in high-speed forward flight,
the helicopter pitches up or down
momentarily.
Elevator damping gain is too low.
Helicopter tends to oscillate
rapidly. (Test by giving a sharp
elevator or aileron command, and
then release of the stick)
Damping gain is too high.
While in high-speed forward flight,
the heli sometimes oscillates in
aileron.
Aileron damping gain is too low
(Warning: too-high damping gain is
hard on servos), or Hiller is too high.
Helicopter hesitates in elevator
and aileron, and continues to
move for a bit when the stick is
released.
Bell gain is too low relative to Control
Rates. Increase Bell gain slightly, or
decrease Control Rates.
After an elevator or aileron change
the rotor disk springs-back after
the stick is released.
Bell gain is too high relative to Control
Rates.
Responds too sharply to aileron or
elevator.
Bell gain is too high.
©2010 Skookum Robotics, Ltd
52
Symptom
Problem & Solution
Random jitter or jumps in roll
and pitch, or tilts at one
particular rpm.
Vibration effects on the gyro. Make sure
it is mounted on good damping tape
and doesn’t contact the frame. Also
check for tail rotor vibration.
Can not set Hiller very high
without causing oscillation,
especially with high head
speeds.
Lack of servo speed and/or precision.
Rotor head mechanics should use full
servo throw for desired cyclic pitch
range.
Aileron or Elevator don’t give
fast enough roll and pitch rates.
Increase Control Rate gains. You will
then likely have to increase the Bell
gains by a proportional amount.
Aileron or Elevator give roll and
pitch rates that are too fast.
Decrease Control Rate gains, and then
decrease the Bell gains.
Cyclic feels mushy in the centre.
Reduce control dead-band.
Not perfectly locked in hover.
Try higher control dead-band.
Helicopter drifts slowly in
elevator or aileron with cyclic
stick centered soon after take
off.
Radio receiver centering drift. Many
receivers’ center points drift with
temperature, up to 3 ticks of trim. Use
transmitter trims to correct.
Helicopter drifts slowly in
elevator or aileron with cyclic
stick centered after several
minutes of flight.
Gyro temperature changing too quickly,
or receiver drift. Make sure the gyro and
receiver aren’t mounted near heat
sources, and let it acclimatize to field
temperature.
Helicopter “jumps” in pitch or roll
after hard changes between
positive and negative collective.
Check that the heli’s centre of gravity
(CG) is directly under the main shaft,
equalize swash servo throws, and
check tail drag compensation.
During piros with collective pitch
changes, or piros during forward
flight, the helicopter wanders.
Servos are not fast enough, or heli
needs to be better tuned for 3D. See
section 17.
