Adding servo to control


How do I add servos to control? For example, I am using AP_MotorsCoax. In AP_MotorsCoax.h I see

SRV_Channel         *_servo1;
SRV_Channel         *_servo2;
SRV_Channel         *_servo3;
SRV_Channel         *_servo4;

Do I just add another line with *_servo5? Do I need to modify anything elsewhere except for AP_MotorsCoax.h and also adding _servo5 in AP_MotorsCoax.cpp? What would be the pins for _servo5? I tried to add _servo5, but it kept giving an error. Therefore, I want to ask if I need to add lines elsewhere.

Thanks in advance