I attempted a risky 3DR Solo flight over water yesterday (whole flight in Fly/Loiter mode). Launched from the shore with some tree cover with sufficient satellites (11 or 12 I think). The flight over the open water with a clear view of the sky went fine. Everything — including beautiful footage — went as expected.All was well…until I turned back to land.

Bringing the Solo back to the landing site in between two trees (flying toward me, so reverse controls), it suddenly beeped and drifted to my left heading into a nearby, convenient tree. I say convenient because it kept the Solo from landing in the water instead. It struggled and then tumbled down the trunk about 10 feet to the ground. Besides a couple of broken props, I think all’s well (haven’t tested the gimbal yet).

So, what happened? I’ve downloaded the datalogs to Mission Planner and reviewed in the log viewer (still learning how to use this tool). Here’s the GPS data (num sats and HDOP) near the end of the flight:

solo gps

The number of satellites dropped from 12 to 9 and then to 8. The HDOP went from 1.6 to 2.3 (at its worst). As I recall, when the Solo drifted (fast) to my left, I hit the “Pause” button on the controller which the AltHode mode marker seems to indicate. I may have then tried to manually correct with the flight stick and, likely in a panic, pushed the wrong direction. But, I think this — if it happened — was after the Solo had gravitated well on its own toward that tree.

My questions:

  1. Did I do something wrong (besides the exceedingly obvious choice of launch site)?
  2. What is the threshold HDOP for “safe” flight of Solo? Is it 2.0? How can we assess marginal launch sites before taking off?
  3. What is the default behavior when HDOP rises above 2.0? …I’m assuming that the Solo got an incorrect location (likely to my right, so the Loiter mode, thinking it was drifting in the wind, moved it to the left) and headed in the “wrong” direction.
  4. It appears that the “Pause” button is useless if the GPS readings are off. Is that correct? I’m assuming that only a switch to full manual would have kept me from crashing.

So, my take home lesson — no flights under trees or other marginal GPS conditions in Fly/Loiter mode; only attempt in full manual flight.

Thoughts?Please feel free to leave your comments below.

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