Filter Attenuation (dB) and Phase Delay Thresholds in Ardupilot

ArduCopter Copter 4.5
1

Hello, everyone. I’m currently tunning a four-rotor drone. In the filtering process, I’m using online FFT filtering. The only aspects that trouble me regarding filtering are as follows:

By using Ardupilot filter review tool

  1. Judging from the curve, generally, at what negative value in decibels (dB) of attenuation can we consider that it doesn’t affect the system?

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  2. Adding a filter will inevitably cause a delay. So, looking at the phase curve in the Ardupilot web tool (filter review tool), what magnitude of phase delay can be regarded as reasonable?

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I’ve read many articles in the Ardupilot wiki, but this threshold value has never been mentioned. I sincerely hope that someone who knows about this can offer me some help.

Thereby enabling the configuration of better filters while controlling the delay.

I’m uploading a LOG file which adopts online FFT filtering. I hope it can be used as an example to illustrate the setting of the entire filtering threshold.

2

-50dB is the value you seek

1 Like
3

ok, Thanks,Does anyone know the threshold of phase lag?

4

@amilcarlucas
An improvement suggestion: Do you think you could add that guidance to section 8.1 of your tuning guide located here: How to methodically tune any ArduCopter | MethodicConfigurator

I remember having the same questions about how to know when the notch filter tuning is done with regards to the decibels and phase lag.

5

done: docs(tunning guide): add note about -50dB noise level · ArduPilot/MethodicConfigurator@5e5b914 · GitHub

1 Like
6

Get the -180° crossing point frequency as high as possible.