Better GERMS stats



Another day, another couple of indoor test flights, experimenting with the IMU accelerometer low pass filter, to see if that would help extract the GERMS info.  Previously, it was set to 2 (92Hz bandwidth); today I tried 4 (20Hz)

The good side is it clearly did – the acceleration and deceleration now stands out clearly at the 1.5, 3.5 and 5s points corresponds to the transitions to ascent, hover, and descent.

Also there was no horizontal drift – during yesterday’s flight, there was drift of half a meter or so. ¬†Clearly yesterday some of the noise on the accelerometer X and Y axes had contributed to the X and Y axis velocities leading to horizontal drift.

The down side is that the lower bandwidth also filtered out some of the Z-axis real acceleration, so during nominal “hover”, Phoebe actually continued to climb slightly- that’s why there’s no spike at 7.5s like yesterday’s graph; Phoebe was still in the air when the flight ended so the post-flight ground impact didn’t register in the stats.

The gyro does offer a dlpf setting for each axis in the MPU-9250; it’s a shame there’s only a single setting of the accelerometer covering all 3 axes.

At least it seems like my GERMS filter idea could work in principle, even if in practise the MPU-9250 can’t be configured to play nicely together with the GERMS filter.

I’ll try 3 (41Hz) accelerometer DLPF tomorrow to see whether this is the perfect comprise.


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