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

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.



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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  • Cutting the throttle will command the Solo to descend at the maximum rate (PILOT_VELZ_MAX). If this rate is set too high the descent will become unstable - which can happen pretty quick.

    I don't own a Solo, just a homemade Copter with Arducopter so I tuned my descent rate myself. You should expect correct rates from a 3DR made copter

  • 3702106052?profile=original

    Hi Eric,

    from my point of view you panicked ;(

    The magenta line shows the RC Input on channel 3 which should be the "Thrust" - it looks like you actively pulled it full down. You can see the yellow "RC out" fighting this command as you are in ALT HOLD mode. This mode just holds the altitude but does nothing to position.

    A bit strange is the fact that channel 3 went from 1000 precisely up to 1450 and stayed on this value. After this jump the Solo went wild - you did not switch the remote off?


    Num of sats dropped a bit and HDOP went up but still quite fine figures. Because you did not use a GPS related flight mode the channel 3 drop might be the biggest cause of the accident.



  • The simple truth, Eric, is that you are right - it is fixable and shouldn't do that.

    All the other stuff is fluff. 

    When they will fix it and how is another story. 

  • I also agree with comments about safe flying and knowing how to fly in non-GPS/barometer flight modes (stabilize or full manual). I have a Husban and two built-from-scratch quads (APM and Naze32) that I also fly.

    That said, most of us (all?) are flying in these assisted modes and need to both know their limitations and help improve them. I believe that the current response of Solo to losing GPS satellites is inadequate and potentially dangerous and that the Pause button on the Solo controller gives a false sense of security in this situation. How can it be improved?

    For starters, I'll personally be following the suggestion to program the A or B button to Manual or Stabilize and will practice this transition.

    However, I think 3DR can improve the Solo by adding additional logic to the Pause button by selectively switching into AltHold or Stabilize depending on one or more criteria such as GPS health. I think this would lead to more predictable behavior for the pilot.


    • I too have been beating that drum since the introduction of the Solo. Every chance I get I tell new owners to program A or B to at least manual. This whole 'Pause' button as a security blanket thing is not working. When many of these new owners to MRs get in trouble, it is often in the yard of their home with limited view of the sky at altitudes under 10'. We have all seen the reports of 'it was flying fine then all of a sudden went crazy and flew in to ___! I was hitting Pause but it wouldn't respond!". Well, Doh.. If 'Fly' mode is not working for you, then pause isn't going to do anything either since it is the same mode!

      I like Eric's idea of trying to add some logic to the pause button. If GPS status is not equal or better than what is required to arm, then go to manual mode. I think this could save a lot of problems new pilots are having and blaming everything but themselves.

  • Bottom line is relying on GPS modes is only as good as the GPS data.

    My A button is set for Stabilize/Attitude mode for the case where GPS fails, I'm in control.

    Practicing going from FLY to FLY:Manual or Stabilize/Attitude is a really good thing to know.

  • Wow, almost the same exact scenario happened to me. Had an incident with a flight prior where I thought Solo was going to overshoot its home position on a RTL. Hard to tell when its 100FT up. Anyway, I panicked and hit FLY:Manual which I have programmed to a button. Well, momentum took it over some trees and I lost sight but was able to get her down safely. Never used the Pause button. Didn't even think about using it. Lesson learned... Well, until the next flight. This time I was ready to hit Pause if I got into trouble except the trouble I encountered was a reduction in satellites/HDOP after I interrupted a RTL about 5 feet off the ground using the PAUSE button so I could manually land. I was near some trees so Solo started to drift under them and started going down my block due to loss of some GPS. What do I do? I hit PAUSE again of course! Wrong! Should have went with Fly:Manual and that minor crash could have been avoided. Luckily I was able to sort of steer the Solo over some grass but it touched and flipped. No damage but god damn Solo in my opinion takes too long to cut the motors. It should know its upside down immediately no? Why not cut motors sooner? Not like I was in Acro mode or anything.

    I dont think you should map Stabilize. Use Fly:Manual instead so that the Solo will hold its altitude. Regarding the statement you made regarding ALT-HOLD its true that Solo would control throttle to keep altitude constant but I dont think that implies that you couldn't drop the throttle on the sticks and affect Solo.

    • my general tip for save flying,

       * NEVER NEVER NEVER trust gps and barometer!!

       * never fly take-of ore land in some auto mode if you can not do this also for sure manually. you must stay tuned to recover the vehicle in each situation while auto take of or landing. so imo this modes are only to use for very experienced pilots

       * first learn to fly the vehicle, in (stabilise or acro mode), for sure in each orientation! in acro you learn also how this vehicle feels to fly and how different moves will work and which aerodynamic affect they have.

      start flying with auto modes only if you can recover, in manual mode, your vehicle from each position.

      this is important!! not so much for your vehicle. more to secure the environment against flying mistakes. i see many videos on youtube where people fly straight into other people, cars, trees and buildings because they lost control or better they never really control their vehicle. especially the phantom pilots:). most of them can not fly an rc vehicle and also do not know anything from the kinetic energy which is inside this 1-2kg mass. 

      hopefully this sounds not to much like a senior teacher. but since the period of phantom pilots starts out in the wild, company's like dji and now also 3d robotics try to sell there products as easy to fly for everybody. and for sure everybody can ride a skateboard in a big pipe. but to do this everybody have to learn this. even if the new skateboards have an autopilot inside. for sure it need a lot of experience to use autopilot systems in a secure way. this require a lot of knowledge which a pilot have to learn. imo this is more difficult than simple learn to fly an vehicle in complete manual mode.  

      so IMO, fly only gps and barometer dependent modes if you are higher plus an secure hight from around 10 meters over the top level from buildings or trees.

      if you fly near groundlever, 2-10 meters over ground while using some auto-mode which use barometer for altitude stay tuned on flight mode switch that is possible to switch immediately back to stabilise or acro mode.

      over water:

      if you change the ground. for example you plan to fly early in the morning from shore over an lake. and you think i will fly only a few meters over ground lever(lover 10 meters), do this in stabilised mode!! if you change the ground from land to water sometimes barometer dependent altitude can drop dramatically.



    • I dont think anyone should be practicing flying their $1000 Solo in Acro mode. I would suggest buying a toy quadcopter like a Hubsan or Nano or something and practice. That's what I did. My Solo sat in the case for 3 weeks after it arrived while I read everything I could. I practiced with the toy drones every day for a month until I my piloting skills were solid. 

  • 3702101249?profile=original

    This is my attempt at analysing the log. This graph shows the 3 events that happened in this sequence:

    1. Mode switched from Loiter to Alt Hold. At this point all was still good, except that the quad's position is now controlled by the pilot and not the controller / GPS anymore. Not sure if you switched to alt hold manually or if it was a result of losing GPS lock. 

    2. The red line shows a full throttle cut. 

    3. Lack of thrust on motors caused it to loose control and it started to tumble soon afterwards as shown in the roll and pitch graphs.

    It looks like the sharp right roll (your left) only followed after the throttle cut.

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