Specifications

at x degrees per second" and the heading hold gyro will automatically use the correct amount
of tail pitch to create this tail motion and compensate for wind and other external factors which
affect the tail.
Note that the revo mixing MUST be disabled for the heading hold gyro to work properly. If the
revo mixing is enabled, then the heading hold gyro will interpret it as a signal to turn the heli-
copter.
30.1.7.4. The difference between yaw rate and heading hold gyros
Imagine we have a helicopter with a properly configured yaw rate gyro and the motor is discon-
nected and it is on the ground where it cannot turn. If we hold left rudder on the transmitter for
one second and then center the stick, the servo will move to one extreme servo position for
one second and then center.
Now, imagine we have the same helicopter with a properly configured heading hold gyro, and
the motor is disconnected and it is on the ground where it cannot turn. Imagine that the setting
for this heading hold gyro is full left stick is 180 degreees per second.
If we hold left rudder on the transmitter for one second and then center the stick, the heading
hold gyro will know the helicopter should turn counterclockwise 180 degrees.However, since
the helicopter is on the ground and cannot turn, the tail servo will stick at one extreme and stay
there - the heading hold gyro will keep trying to turn the helicopter. If we manually pick up the
helicopter and turn it counterclockwise 180 degrees, the servo will finally center.
Note that both types of gyros only stabilize YAW. Neither type of gyro will stabilize roll or pitch.
Technically speaking, a helicopter gyro contains an angular acceleration sensor for only one
axis.
30.1.8. GY-series gyro technical info
30.1.8.1. GY401 setup
There are six adjustments on the GY401: direction, DS, delay, limit, gain and pirouette rate.
The delay and limit are controlled by trimmers on the gyro itself. The gain adjustment is con-
trolled at the transmitter by setting the value of the gyro channel, and the pirouette rate is set
by adjusting the endpoints of the rudder channel.
30.1.8.1.1. GY401 direction switch
For a heli with a tail servo, the GY401 direction switch configures the direction the gyro moves
the servo for clockwise and counterclockwise movement.
For a heli with a tail motor ESC, the GY401 direction switch configures whether the gyro
moves the throttle up or down to turn the heli clockwise or counterclockwise.
For both heli types, If this switch is set incorrectly, the heli will pirouette wildly and out of con-
trol.
30.1.8.1.2. GY401 DS (digital servo) switch
The GY401 DS switch allows the gyro to update a digital servo about 4x faster then a normal
servo.
Do not set this switch unless you are using a servo which supports a 270 hz frame rate, such
as the S9253, S9254, or Volz Speed-Maxx.
Technical Appendix
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