©2008 Skookum Robotics, Ltd
21
16 Tuning Troubleshooting Guide
Symptom
Problem & Solution
Heli 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
using the Swash Mixing setup values,
or increase servo travel.
After a sharp elevator or aileron
command is released, the heli
oscillates slowly.
Hiller gain is too high.
While in high-speed forward flight,
the heli pitches up or down
momentarily.
Elevator damping gain is too low.
Heli 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.
Heli 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. Decrease it slightly, or
increase Control Rates.
Responds too sharply to aileron or
elevator.
Bell gain is too high.
Heli precesses in hover (a motion
like a child’s spinning top as it
slows down). Gets worse with
higher Hiller gains.
Interaction between the Elevator,
Aileron, and Yaw axes. Check that
the SK360 gyro and the yaw gyro are
both mounted correctly. Also check
phase angle.
©2008 Skookum Robotics, Ltd
22
Symptom
Problem & Solution
Random jitter or jumps in roll
and pitch.
Vibration effects on the gyro. Make sure
it is mounted on good damping tape,
and doesn’t contact the frame. Also
check for tail vibration.
Can’t set Hiller high enough
without causing oscillation,
especially with high head
speeds.
Lack of servo speed, precision, or the
frame rate is too slow. 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 slightly.
Aileron or Elevator give roll and
pitch rates that are too fast.
Decrease Control Rate gains, and then
decrease the Bell gains slightly.
Cyclic feels mushy in the centre.
Reduce dead-band.
Not perfectly locked in hover.
Try higher dead-band.
Heli 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.
Heli 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.
Heli “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,
and tune swash servo throws and tail
drag compensation.
During yaw piros with collective
pitch changes, or piros during
forward flight, the heli wanders.
Damping gains are too low, servos are
not fast enough, swash moves
unevenly, or
tail drag compensation
needs tuning (see page 19)
.
