Trio Avionics EZ Pilot - v 2.3 - Manual (Page 29)

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7.0
Servo
The servo unit incorporates two very important safety features:
• The internal gears are pulled into the engaged position by an electric solenoid. When the
gears are not engaged, the output crank arm rotates freely and the aileron controls can
be operated normally. When the servo is engaged, the solenoid pulls the gears into
place so the servo has control of the ailerons. Disengaging the servo allows free
movement of the aileron controls.
• The servo is engaged and disengaged by pressing the SERVO button on the EZ Pilot
control head. There is also a provision to accommodate a remote SERVO
DISCONNECT switch on the control stick (or other remote location). Installation of a
remote switch is highly recommended, as it allows a convenient and an immediate way to
disengage the servo - even in heavy turbulence, when it may be difficult to operate the
small SERVO button on the EZ Pilot control head.
• The servo also employs a clutch, which allows the pilot to override the servo by applying
moderate force to the control stick. Even though the solenoid will hold the gears in place,
the clutch will then slip and allow the control surfaces to move. In the event of strong
turbulence, or an autopilot anomaly, the pilot can thus override the servo to control the
airplane. In such an instance, the servo should be disengaged as soon as possible.
NOTE: The clutch function does not rely on a shear pin failure mechanism as is employed on
some other popular autopilot servos. Activation of the “clutch” function in no way damages the
servo drive system although prolonged operation in this condition should be avoided.
The entire job of the servo is to have the power driven crank arm, which is linked to your aircraft
aileron controls, push the stick left or right when the autopilot requests aileron adjustment. That’s
all. Further discussions simply relate to ways to do this, and to facilitate the installation.
7.1 Installing the Servo
Begin by looking for a point where pushing or pulling the aileron control linkage a distance of 1.5
to 2.4 inches will do the job. Then find a place to mount the servo nearby to accomplish this by
means of the pushrod. You will mount the servo and pushrod so that the ailerons are neutral
when the servo crank arm is at mid position. That’s it, aside from carefully checking that the
required range of aileron movement is transited within the limits of the servo travel range and that
no “over center” condition can exist.