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Robertson AP45 Autopilot
Design and theory of operation
Simrad Robertson AS
Egersund - Norway
Page 3-3
The rudder feedback unit transmits rudder angle information to the control unit
and rudder angle indicators. It is mounted close to the rudder stock and
mechanically connected to the rudder tiller arm by a transmission link.
The RF45X contains a circular PCB carrying all the electronics and a long life
potentiometer connected to the PCB by three wires. The unit is repairable in that
the electronics and the potentiometer can be replaced.
The electronics have two output circuits. One circuit outputs frequency of 3400Hz
as midposition reference. It varies at a rate of 20Hz/degree, increasing when the
rudder moves to port and vice versa.
The other circuit outputs a current (0.1-1.1mA), to the rudder angel indicator(s)
(RI35 and RI9).
The RF45X is supplied with a fixed 4-wire, screened cable of 2 m (6 ft.). This cable
is meant to be spliced in the enclosed splash-proof junction box.
The shaft of the feedback unit is free to travel 360 degrees, but only ±70 degrees
from midposition are used for signal control.
The transmission link mechanically connects the feedback unit to the rudder tiller
arm. It is made of stainless steel and has standard length of 450 mm.
Fig. 3-4
RF45X principle
The RF14XU Rudder Feedback Unit consists of a glass-reinforced fire inhibiting
polyester housing with a mounting plate of seawater resistant aluminium.
Potentiometer, limit switches and an electronic drive module are also contained in
the unit. The electronic drive module comprises a voltage section and a frequency
section.
The voltage section outputs a voltage to the rudder angle indicator(s) which is
proportional to the rudder angle. The voltage varies ±9V with half of the supply
voltage as reference. The voltage should read zero volts with the rudder in
midposition.
The frequency section outputs a signal to the control unit with 3400 Hz as
midposition reference. It varies at a rate of 20 Hz/degree, increasing when the
rudder moves to port and vice versa.
The shaft of the Feedback Unit is free to travel 360 degrees, but only ±90 degrees
from midposition are used for signal control.
Rudder Feedback
Units
RF45X Rudder
Feedback Unit
RF14XU Rudder
Feedback Unit
(optional)