Hi,
What are the AP configuration parameters for a 4WD (direct drive) rover?
I am using 4x brushed motors and 4x ESC connecting to the power module, one of them powering the servo rail.
You do not need 4 ESCs for four brushed motors. One ESC for each side should be enough for a skid steering rover. If you plan to use mecanum wheels in the future, you will need 4 ESCs.
No matter how many ESCs you use, you must configure a matching number of servo outputs as “throttle left” and “throttle right” and connect the ESC signal cables accordingly.
And the parameter settings for skid steering are
SERVO1_FUNCTION = 73 (Throttle Left)
SERVO3_FUNCTION = 74 (Throttle Right)
as given here http://ardupilot.org/rover/docs/rover-motor-and-servo-configuration.html in the Skid Steering section.
Connect your left side ESC(s) to PWM output 1 and the right to PWM output 3.