I just finished building my first quad using APM 2.6.
I did all the calibration process and when I planned to do the test flight and gave some throttle I noticed that motor #4 spins slower than the others.
It’s the first quad I built using APM 2.6. I completed all the setup procedure and when I tried to do the test flight and raised the throttle the motor started to work but very slowly (like 10% from the max power).