I wanted to post on this thread because I would like to show a plot from a recent log that occurred on a drone running two Here4 units. I know that it was mentioned that flight with Dual Here4 is acceptable, but based on this, I’m not sure I can agree. I have seen multiple Here4 failures and all have generally developed in the same way. First, the values of one or multiple magnetometer axes start to get noisy and grow very large, which does cause lots of EKF switching during flight, especially if it happens to the primary compass. Usually, after this failure happens in flight, the subsequent power cycle of the drone results in the compass being “offline” (i.e. the mag data is not showing anymore on the DroneCAN node). If it were such a rare occurrence, I would agree that a failure mode is predictable and can generally be handled without too much issue by having a backup. However, this particular log shows that there is a failing Z axis magnetometer on the secondary mag (MAG[1]) and towards the end of the flight, the Z axis of the primary mag (MAG[0]) starts to show this same failure mode:
The next attempt to power up after this log resulted in MAG[1] missing, but MAG[0] still failing.
I’ve also seen this post, which is presumably related (at least the part about the missing mag data): Here 4 Compass Error RM3100: BIST failed 0xBF - #2 by Dawid_Zielonka
One person there mentions at least 15 of them having failed, which seems extreme. With multiple reports of this type of failure, I also can’t imagine we are all doing something fundamentally wrong with the installation or build.
Mostly I am simply hoping to gain some understanding about what is going on here. I have sent multiple failed units to our reseller who communicates that they’ve been sent to CubePilot, but I have so far not been able to gain any insight into the mode of failure.
Please let me know if this information is helpful, or if there have been additional learnings about this issue.
Thank you.