I’ve broken Phoebe’s wrist twice in the last few days.  I had spares from when I swapped her default red arms for black, but still…

I was baffled why; her code intends for a 1.5m take-off over 3s, hover for 3s, and land over 5s (to guarantee touchdown), and she’d been doing that beautifully.  And then suddenly she wasn’t – she was rising to 3 or 4 meters, and continuing to rise when she’s supposed to be hovering.  That’s when I hit the kill switch she broke her wrist falling from 4m onto the kids play slide / swings – twice.

Finally thank heavens, it dawned on me.  As part of rebuilding her legs, I took them off completely, which allowed me to swap the breadboard with the smaller one with neoprene rubber padding for noise suppression – and critically a new (identical) MPU6050 breakout.  Except it wasn’t identical, and it needed gravity to be recalibrated as the stored values related to the old sensor.  Because I hadn’t, even when she was flat on the ground, she was read -1.1g instead of -1.0g on the vertical axis – that meant that throughout the run there was an additional 0.1g vertical power being applied to meet the +1g target.  0.1g might not sound much, but that means 0.1 * 9.81m/s/s, meaning actually she climbed faster in takeoff and continued climbing but slower in hover.  I suspect had I not hit the kill switch, she’d not have started descending in landing mode, but hovered at best or continued to climb gently at worst leading to an even more damaging landing.  So anyway, lesson learnt – recalibrate gravity if you swap identical brand sensors over.

Tomorrow’s weather is looking better so I hope to get some safe flights done and see the effect on my noise filtering, and hopefully from there, get back to drift management / non-horizontal ground take-offs.

Wish me luck!

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