Betaflight New Filter!

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Quadcopter

Starting with Betaflight (BF) 3.3.x there is a new filter introduced by BF developers that promises significant difference in flying characteristics of a quad. Unfortunately, to use it is not as simple as clicking a button. There are few steps that needs to be done to enable this new filter:

Before we go through all the steps required, below are the checklists if you have proper Flight Controller (FC) or not:

  1. at least FC with STM32F3 chip (F4 is recommended).
  2. please note type of gyro chip used on the FC.

Although the hype currently is regarding the use of Kalman Filter in flight controllers for smooth flight, the disadvantage using Fast Kalman Filter (FKF) is that it requires a minimum of STM32F4 chip on the FC.

BF developers came up with alternative optimized filtering method which uses less computing load on the flight controllers and not much juicy difference compared with FKF implementation. This means that Betaflight enables up more Flight Controllers that can utilized this new filter.

To utilize the new filter, there are steps you will need to follow (credit to fujin BF developer):

  1. Open Betaflight Configurater (BFC), go to CLI tab and type in these two commands.
    • set cpu_overclock = 192MHZ (only for FC with F4)
    • set gyro_stage2_lowpass_hz = 250
    • type save
    • CLI command settings

  2. Reconnect BFC and go to Configuration tab and enable these functions:
    • if you are using MPU6000:
      • it is recommended to use 8k/8k gyro and PID loop.
    • if your FC uses ICM-series gyros, eg. ICM20602:
      • you should try 32kHz mode
      • click Enable gyro 32kHz sampling mode
      • choose 32k/16k gyro and PID loop
      • enable DYNAMIC_FILTER
    • Configuration tab

  3. And finally, go to PID Tuning tab
    • in Filter Settings, for D-Term Lowpass Filter select FIR.
    • under Profile independent Filter Settings:
      • disable Gyro Notch Filter 1
      • disable Gyro Notch Filter 2
      • disable D Term Notch Filter
    • for FC with MPU6000 only (credit to Sifu Steven & Kogi):
      • set Gyro Soft Lowpass Frequency [Hz] to 0
    • Filter settings

Aaaaaaaaand done… well, just make sure your CPU load is not over 80% (recommended ~50%) and you are ready to experience juiciness!

A good practise to test this (thanks to Sifu Steven) so that you don’t burn your motors:

  • change Gyro Notch Filter 1 only.
  • hover 30 seconds, then check your motors temperature.
  • if motors are not hot, continue fly for a minute, then again check your motors temperature.
  • continue test fly again until remaining of your battery.
  • repeat for Gyro Notch Filter 2 and D Term Notch Filter.

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