Hi i am using 4.5.7 version arducopter , here we have commanded the velocity and the vz velocity where ever exceeds 4m/s one of my motors i.e 4th motor will be very low , iam consfused is the weight distribution not correct (C.G) or any issue with the PID tuning, at low speeds i.e below 10m/s (vxy) the drone performs good but at high speeds 15m/s (vxy) 4th motor goes very low,Logfilehere is the log
It looks to me like there’s either a C of G issue, or there is a twist in the airframe. When hovering the motor outputs should be close (they’ll never be perfect), but servo 4 (Motor 3) is much lower. I would try to fix that before you go and chase higher speed runs.
This is likely a mechanical/physical issue, not a configuration problem.