Low frequency noise using imu_cuttoff and

Pixhawk
1

I am working on a coaxial quad Drone production. For each drone, I set
IMU_GYRO_CUTOFF and IMU_DGYRO_CUTOFF to filter out noise. I generally see noise at 50Hz. Here is an example

Actuator FFT
Actuator FFT924×368 44.6 KB

Every drone has dampper installted to reduce the noise. Now in few drones I see low frequency noise 0-40Hz. Everything is the same Frame, Motor, Prop, Esc and same dammpers is install as the others Drone. I try to use static notch filters to cutoff low frequency
IMU_GYRO_NF_FREQ = 25Hz
IMU_GYRO_NF_BW = 15Hz
I see minor stability, but it is unsatisfying. Here is the log
Stabalize_Flight
Altitude_Flight
Actuator FFT
Actuator FFT924×368 44.7 KB

2

Everything under IMU_GYRO_CUTOFF will not be filtered.
If this is a drone with large motors and low KV it is likely the propeller passing frequency and the correct way to address is is dynamic notch filtering via e.g DSHOT or CAN telemetry data.

If that is not the case and your motor vibrations are >80Hz there is some frame resonance. Ensure legs etc are fastened correctly.

3

I am using the following
FC: CUAV X7+ Pro
Motor: MAD Swift CM4320 V1 KV380
ESC: Hobby Wing-60A
Prop: Gemfan 13X10 3-Blade
Drone Size: 775mm x 775mm x 184mm
Weight: 17 kG