My current (just for fun) project is a small, 5’’, sub-250g quad with a Raspberry Pi Zero and a camera on board for mapping, equipped with a mro PixRacer.
After some manual tuning and a Autotune flight it was flying reasonably well in AltHold and Loiter modes (maybe reacting a bit slow when stopping in Loiter). Vibration values also look good, below 14 on all axes.
However, when flying a test mission in Auto, after a bit of steady and nice flying the Copter suddenly jerked violently and lost altitude rapidly. It caught itself after some meters of falling and I was able to fly it back using RTL and land it safely. After that, tried flying it in Loiter some more and everything behaved normally again.
Looking at the log, I see the following:
- Arming checks should be full - I forgot to add GPS back in after testing it indoors. But GPS reception looks good throughout the flight, with a single GPS glitch after landing.
- Vibrations look ok up until the incident. Only during/after the violent descent there is increased vibration/clipping
- the Power Supply for the Pixracer looks poor, with Vcc going down to 4.86v. But I don’t see a correlation with the problems during automatic flight. I will try to find a better solution for powering the Pixracer (and still keeping the copter lightweight)
- Just before the descent the Pressure drops rapidly/Barometric altitude rises from 50 to 100 m and then oscillates at an extreme amplitude (GPS altitude is representative of the Copters actual behaviour)
It should be noted that the Pixracer is uncovered on top of the Copter. Can this be the reason for this sudden drop in pressure? It’s strange because it behaved well during the manual/loiter tests.
I’m a bit puzzled because of the very extreme and sudden reaction of an otherwise well-flying copter.