RC input and output
ArduSub is designed around two independent concepts of RC Input and RC Output. RC Input is an array of control channels representing pilot inputs like forward and yaw commands. RC Output is an array of channels representing the pulse widths to write to individual servo output pins. Although ArduSub does not support the use of RC receivers, the logic is the same and is applied to joystick inputs instead. Joystick input and RC Input are synonymous in ArduSub.
These are the default channel mappings for RC input:
|9||Lights 1 Level|
|10||Lights 2 Level|
On the Pixhawk, there are 8 main outputs and 6 auxillary outputs. The main outputs are updated at 200Hz by default (configured via the RC_SPEED parameter), and the auxillary outputs are always updated at 50Hz. It is important not to connect analog servos to the main outputs, because the very fast update rate can cause the servo to burn itself out.
By default, aux outputs 5 and 6 (SERVO13 and SERVO14) are reserved as GPIO pins to be used for relays, and will not output a pwm signal for other functions. This is configured with the BRD_PWM_COUNT parameter, which determines how many of the auxillary outputs to configure as PWM outputs (default is 4).