Back on the wagon

I’ve flown my Mavic probably for 20 minutes over the course of 5 short flights simply to get familiar with the controls while dodging the rain showers of the last couple of days.  I’m back inside again trying to track down why Hermione has started throwing her I²C wobbly again.

Motion processing is working well, keeping processing close to the minimum 100Hz regardless of other sensor inputs – here 156 samples were processed in 1.724s.

Processing rate

Processing rate

Garmin’s height is running stably at the intended 20Hz and it’s well withing the accuracy possible for distances less than 1m

Garmin LiDAR v3

Garmin LiDAR v3

Here’s the problem though: the IMU is fine for 862 samples averaged into the 155 motion processing blocks, showing just gravity as Hermione sits on the ground, but suddenly the IMU values spike for no reason for the 156 sample average.  Note that this happens only when the Garmin is plugged in.  There are in fact two spikes: the first is shown, the second causes an I/O exception and the diagnostics are dumped:

IMU stats

IMU stats

I’ve tried power supplies up to 3.4A, both battery and mains powered; I’ve resoldered various critical PCB joins; I’ve added the 680uF capacitor as the Garmin spec suggests despite Zoe being fine without it, and I’ve used a newly flashed SD card, all to no avail.

I have two things left to try:

  • currently the Garmin is read every motion processing loop, despite being updated at 20Hz; the spec says there’s an interrupt, but as yet, I’ve not got it to work.  Must try harder!
  • Failing that, I’ll have to replace the MPU-9250 with another, and see if the current one is faulty.

Beyond these two, I’m out for ideas.

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