The FFT tune switch tried to set the notch filter from a hover
What ArduPilot says:
- FFT: Notch frequency N.NHz and ref N.N selected
- FFT: Selected N.NHz
- FFT: Unable to start FFT averaging
- FFT: Found peaks at N.N/N.N/N.NHz
- FFT: Unable to set throttle notch with N.NHz/N.N
- FFT: Unable to calculate notch: need stable hover
A switch set to “FFT Tune” (RCn_OPTION 162) averages the gyro noise while it is high and, when moved back, works out a throttle-based notch filter from it. “Found peaks” lists the noise peaks, “Selected” the lowest one that the others are multiples of. “Notch frequency … and ref … selected” is success: frequency, hover throttle and harmonics were written to the notch and saved. “need stable hover” means no peak or no hover throttle was found. “Unable to set throttle notch” means no notch is in throttle mode. “Unable to start FFT averaging” means the analyser could not begin.
What to do, most likely first
The switch was moved back on the ground, or after a few seconds of manoeuvring instead of a steady hover.
FixHover steadily in a mode that holds height, switch high, wait 20 to 30 s without touching the sticks, switch back, then land.
No harmonic notch is set to follow throttle, so there is nothing for the result to be written to.
CheckThe message is “Unable to set throttle notch”;
INS_HNTCH_MODEis not 1.FixSet
INS_HNTCH_MODEto 1 (throttle), reboot and repeat the hover. With ESC telemetry the notch is better driven by motor RPM, and this switch is not needed at all.The analyser itself is not running.
Check
FFT_ENABLEis 0, or an FFT memory or self-test message appeared at start-up.FixSet
FFT_ENABLEto 1 and reboot; solve any FFT message from start-up first.
The result is saved straight into the notch parameters. Compare them with a log of the hover before trusting them: a wrong notch frequency adds delay and filters nothing.
Parameters to look at
| Parameter | What it is |
|---|---|
FFT_ENABLE | Enable |
INS_HNTCH_MODE | Harmonic Notch Filter dynamic frequency tracking mode |
INS_HNTCH_FREQ | Harmonic Notch Filter base frequency |
INS_HNTCH_REF | Harmonic Notch Filter reference value |
INS_HNTCH_HMNCS | Harmonic Notch Filter harmonics |
FFT_MINHZ | Minimum Frequency |
FFT_HMNC_FIT | FFT harmonic fit frequency threshold |
Where to do it:Setup & Tuning GuideSetup & Tuning Guide
The code that sends it
FFT: Notch frequency N.NHz and ref N.N selected
libraries/AP_GyroFFT/AP_GyroFFT.cpp AP_GyroFFT::stop_notch_tune() · Open in ArduPilot Copter-4.7.1
FFT: Selected N.NHz
libraries/AP_GyroFFT/AP_GyroFFT.cpp AP_GyroFFT::stop_notch_tune() · Open in ArduPilot Copter-4.7.1
FFT: Unable to start FFT averaging
libraries/AP_GyroFFT/AP_GyroFFT.cpp AP_GyroFFT::start_notch_tune() · Open in ArduPilot Copter-4.7.1
FFT: Found peaks at N.N/N.N/N.NHz
libraries/AP_GyroFFT/AP_GyroFFT.cpp AP_GyroFFT::stop_notch_tune() · Open in ArduPilot Copter-4.7.1
And 2 more messages, sent from the same places.