RPM Sensor Based Dynamic Notch Setup¶
Setup an RPM sensor.
Set INS_HNTCH_MODE and/or INS_HNTC2_MODE = 2 or 5 to use an RPM sensor to set the harmonic notch frequency.
Set INS_HNTCH_ENABLE and/or INS_HNTC2_ENABLE = 1 to enable the harmonic notch
Set INS_HNTCH_REF and/or INS_HNTC2_REF = 1 to set the harmonic notch reference value to unscaled, unless the RPM sensor is reporting a fraction of the actual rotor speed. This might occur in a geared drive train setup. If the reported RPM is 1/3 the actual, for example, set this to 0.33.
Set INS_HNTCH_FREQ and/or INS_HNTC2_FREQ = below the hover frequency. In the RPM based dynamic notch, this parameter sets the lower frequency limit of the notch. So even if the RPM sensor reads a lower value, the notch’s center frequency will remained constrainded to the value of this parameter. You can easily determine the hover frequency by performing a hover and looking at the RPM sensor log data (e.g. RPM.rpm1).
Set INS_HNTCH_BW and/or INS_HNTC2_BW = half of INS_HNTCH_FREQ
Checking Harmonic Notch Effectiveness¶
Once the notch filter(s) are setup, the effectiveness of them can be checked by again measuring the frequency spectrum of the output of the filters (which are the new inputs to the IMU sensors). Refer back to the Measuring Vibration with IMU Batch Sampler page for this.
While the log analysis of noise frequencies is not absolutely required prior to notch setup for RPM based mode, the logging and analysis done for the Confirmation flight using that method can be done in order to confirm the noise elimination, if desired.