Solo crash -- GPS issue or...pilot error?

Posted by Eric Compas on September 27, 2015 at 2:31pm

Before you reply with...geez...that was dumb: Ya, I know it was, just trying to better learn from my mistake.

I attempted a risky flight over water yesterday (whole flight in Fly/Loiter mode). Launched from the shore with some tree cover (ya, not good, I know) 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. Even got over the the anxiety I was feeling over flying $2k worth of gear over certain ruin. 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 (over Mavlink -- slow!!) 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:

3691246049?profile=originalThe 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?

Eric

P.S. I've attached the flight log (7-zipped to get under size limit) if anyone's interested.

2015-09-26 10-37-11.7z

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Replies

    • Eric Compas > Jack September 30, 2015 at 6:55pm

      Jack, thanks for looking. Hmmm...I have no idea why the throttle dropped like that. I'm *almost* positive I didn't pull back (on the Solo controller) on the throttle. On further study, I just discovered the "map" option in the log browser:

      3702596493?profile=original

      Here's my interpretation:

      1. As I entered tree cover (blue path on the right in the map), I lost 2-3 satellites (heavier vertical bar at 2827 seconds).
      2. The map shows that the Solo thought it was drifting to the east (my right as I stood under the trees), so it compensated by drifting west (to my left) from 2827 on.
      3. I hit the pause button on the Solo controller initiating the AltHold flight mode. The map shows that Solo still thought it was drifting to my right. In AltHold, the throttle is automatically controlled by the flight controller, so it must have thought it was climbing (and therefore cut the throttle?). Perhaps a result of the rapid loss and gain of satellites under the tree cover?
      4. By this time, neither I or the Pixhawk know what's going on, and tree gravity takes over.

      I still think this crash wasn't my fault (besides flying under tree cover!) and that the Solo could have a better response to losing GPS satellites -- perhaps switch to Stabilize mode?

      I live in a land of trees, so I'll need to develop a procedure that allows me to take off and land with some level of tree cover (as Corbin mentioned, trees were 30' away) and with some level of confidence. I think I'll program either the A or B button to Stabilize and use that mode to take off and land near trees. Other suggestions?

      Thanks,

      Eric

    • Ray Brothers > Eric Compas October 1, 2015 at 3:44pm

      That's a good option. I have my B button programmed for Manual Fly.

  • Gregg September 28, 2015 at 9:54pm

    My iris did the same thing..looses sats, than comes down like a brick. Sold it and bought a Phantom 3 pro. When it loses GPS it goes into ATTI mode..still flyable! Good luck with the world smartest drone!!

    • Eric Compas > Gregg September 30, 2015 at 5:51pm

      I'll stick the Solo -- I'm committed to the open source approach. But, I think this is a fixable problem.

  • Corbin Hambrick September 28, 2015 at 9:07am

    4.  I think that is corrects based on how I read the manual.

    1.  From my experience with 3DR support, they will say it is your fault for flying too close to objects (trees).

    I had to replace a motor because mine started veering towards my trees and the pause button didn't do anything.  Ultimately ended up upside down and burned out motor 4 before I could get it shut down.

    I was flying in my street with tall pine trees nearby but nothing closer than 30 feet.

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