Rudder feedback is useful to prevent the drive motor from stalling. It also provides nmea output of the rudder angle which can be displayed in opencpn.
A typical rudder feedback sensor has 3 wires. These wires go to a potentiometer which changes resistance with rudder angle.
It is possible to use rudder feedback with only 2 wires. In this case, the correct resistor needs to be placed in series with the rudder indicator.
The resistors on the motor controller can be replaced depending on the resistance of the rudder feedback used. Typically a potentiometer from 1k to 20k resistance is used, but if the resistance is higher or lower, different resistor values are needed.
The rudder feedback can be calibrated using either openplotter interface, or pypilot plugin for opencpn.