Coaxial copter Servos are not moving


I built the coaxial copter. Motors is working but servos not moving.
And while I moved roll and pitch stick, motor RPM is varying.

Hardware set up:
I am using pixhawk 1.
servo 1 and 2 are plugged in output 1 and 2.
motor 1 and 2 are plugged in output 5 and 6.

Parameter setup : using latest firmware.
servo output1: RC1
servo output2: RC2
servo output3: not use
servo output4: not use
servo output5: motor1
servo output6: motor 2

I spent the whole day to figure it this but failed.

What is the problem?