How to understand the copter INS_xx_FILTER

ArduCopter Copter 4.0
1

Hello guys!
right now we are tuning a 13kg big copter with:

  • AC 4.0.4
  • CUAV X7
  • 12S 10P NCR18650GA
  • Hobbywing X6 with 2388 props
    we are following the tuning and first take off guide, and the copter is oscillation both pitch and roll axis, so we decide lower the pitch and roll’s P term and I term, after lower the P and I, the copter is not oscillation anymore, So we continue follow the guide we put the copter into altitude hold mode, It’s work pretty well.
    The problem is, when we put copter into loiter and pos hold mode, the copter is little wobble, we have a nmea RTK GPS on it, and we have the rtk fixed. the PID is still not very good.
    But when I read the tuning doc, the INS_ACCEL_FILTER should be 10Hz to 20Hz, I know the big copter should set lower, but how to determine it?
    here’s the log
2

Enable FFT and batch logging. That will allow you to inspect the FFT graphs and set your filter appropriately. It might be a good idea to also set the dynamic notch filters.