I had a bit of a scare testing Loiter on a flat hex powered by KDE 3520-400kv and KDE 55A ESC’s.
After working through the fixed 1100-1900us PWM range, finally changing the PWM output from the throttle channel on the Taranis, I went out for a test flight. The props do not turn when armed, I’m guessing I still need to adjust that. I also have not adjusted the throttle midpoint, as I know that has an impact on hover for any mode using the alt hold subsystem.
The issue is that I saw it climb while in Loiter, so I decreased throttle. It continued to climb so I moved throttle even lower, and even down to 0, yet it climbed even further and faster. I finally switched to Stabilize and obviously in the heat of the moment didn’t think through how much throttle I would need. So it fell out of the sky and I caught it at the last minute to soften the crash with some lateral velocity I could not compensate for quickly enough.
My question is, why did it not descend and in fact climb even with 0 throttle?
Conditions were clear skies with maybe 10mph wind, so definitely not a calm day. I believe that explains the z axis from the IMU’s.
The two “failures” of note in auto-analysis are IMU Mismatch and PM. The Pixhawk is isolated with two strips of Kyosho Zeal, so I will try 4 squares instead. I also may have some servo cable tension. However, I had one other short test flight with a pretty solid Loiter while I was tweaking the PWM range. I have heard the “PM = FAIL” tends to be a red herring with Copter 3.2.
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Here you can see just before the rapid climb that my throttle stick input is at 0. Altitude rapidly increases and throttle output becomes erratic. I recall the wind acted up right then as well, but it seems like the baro was working fine (to my untrained eye).
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Here the IMU’s appear to be fairly in sync with one another, with a lot of z-axis activity during the radical climb and obviously during the crash at the end. Is this indicative of vibration during wind, or something I can fix?
[attachment=1]Screen Shot 2015-07-19 at 7.26.23 AM.png[/attachment]
Here you can especially see my throttle input cut to 0, with a selected motor output becoming quite erratic (they all look essentially like this, so I just picked one as an example):
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What would you recommend I try before attempting another Loiter test flight? The full log is attached for review.