©2008 Skookum Robotics, Ltd
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Helicopter Airframe Setup
Good mechanical setup is critical to the gyro performing correctly. Please read this
section fully.
The gyro should not be used in addition to a flybar, as the results could be
unpredictable. It is intended for use where the swashplate alone drives blade pitch.
Blades:
Flat bottomed rotor blades are not recommended. They have a pitch-down moment
about their axis of rotation that could put heavy loads on the swashplate servos. The
ideal rotor blades will have a symmetrical airfoil, be torsionally stiff but a bit
flexible spanwise, and balanced both spanwise and chordwise.
Servos:
The best performance will be achieved if the swashplate servo’s full normal range of
movement is used. For good “3D” performance, you will need servos that are fast,
and if possible digital. For analog servos, check their specification, and drive them
at 6v (if they are rated for it). Stronger, faster servos will let you use higher damping
gains (see Section 15), which is important for maneuvers such as piro-flips.
Try to have 90-degree angles between servo and blade grip arms and linkage rods,
for even movement. The gyro’s USB setup interface will allow fine-tuning of servo
centers to achieve this.
Rotorhead:
When setting up the mechanics originally designed for helis with a flybar, just
removing the flybar but keeping normal servo arm length will likely give too much
blade pitch action. Either servo travel or servo arm length will then need to be
reduced. For example, on the Align
tm
TREX, you can adapt the flybar mixing arms
as travel-reduction arms on the rotorhead, to reduce the effect of swashplate slop
and reduce servo load. This will allow higher gains, and better performance.
Some kind of anti-rotation or “follower” mechanism will be needed, to keep the top
of the swashplate from rotating relative to the blade grips.
©2008 Skookum Robotics, Ltd
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If the swashplate is not held so the linkage to the blade grips is at 90 degrees to the
blades (for 2-bladed rotors), the phase angle will need to be set to compensate. See
the diagram below.
For initial flights, the phase angle should be adjusted so that when the blades are
lined up with the heli’s tail boom, they do not move with elevator input, but do
move with aileron input (for 2-bladed rotors). This can be set either mechanically, or
through the USB setup software.
It is important that the linkages and swash have little slop and the lowest friction
possible.
How stiff the rubber rotor head dampers are will have an effect on tuning the gyro
and flight performance. Performance will be better with the teeter damping a stiffer
than normal, but too stiff can cause vibration, which is hard on the airframe, gyros,
and servos.
Tail:
Because the axis of the tail rotor disk is lined up with the elevator axis of the heli,
it’s important that you minimize tail rotor vibration. Also, if you have a belt-driven
tail, be sure that your tail boom is electrically grounded to the heli’s frame or motor
case, to prevent static electricity buildup.
Balance:
The gyro will perform best with the CG directly under the mainshaft, or very
slightly nose heavy. This is especially important for maneuvers that use fast
collective pitch changes combined with yaw, such as piros.
