Please help verify cause of RTL

Hello All. First off, thank you to all who have worked so hard for this community!!

I am posting this here(as opposed to the main thread) on the advice of other members.

I just had an event happen with a new quad I assembled.

I know the setup was incomplete on this quad. I had intended to fly only in stabilize to test my camera gimble.

I had an RTL trigger with a resulting significant crash and would like to know why.

If someone could please help analyze my Flash log(no telemetry during this flight) for clues, I would greatly appreciate it.

My setup is as follows:

APM 2.5 with ublox and seperate external compass.

Dji 450 motors and arms and 10x4.5 props with a custom spider style frame.

30amp simon K flashed f30 speed controls from RCmanchild

Tarot Gopro gimbal with separate 1000mah 3s pack

Single 2800mah 3s main pack(incorrectly setup as a 5600mah dual pack in apm)

FRsky tfr4-b receiver with ppm single input to apm

Futaba T8FG transmitter

900mhz 3dr telemetry( Not connected during this flight)

The flight went like this. powered up quad, turned on Gopro(in wifi mode) and took off to get an aerial shot of a bus leaving an event. It was windy, but quad was quite stable. I got up to about 100 feet alt and about 100 feet away and quad did a piroette(spelling?) then stabilized momentarily, then pitch hard forward and away it went from 100' to the ground at about a 25degree angle. I know the logs show RTL triggered. Can someone tell me specifically why?

What I assume was a Radio failsafe. But it appears to me the roll in and pitch in are still registering my stick inputs.

******Attached Tlog is for reference only. It is from my only previous test flight. Exact same config as main event. There is outdoors hovering with GPS lock at about 70% in this Tlog*****

Here is a link to the onboard video from this event.

Onboard view of unexpected RTL


Thank you for any help on this,


2013-09-07 20-41 6.log

2013-09-07 11-07-52.tlog

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  • Developer


        I've had a look at your logs and there are three radio failsafe events so it looks like your tx and rx lost contact (and regained it) a few times.  There's also a compass error in there but that's that as it crashes so perhaps the external compass was ripped off.

    3692839133?profile=original    Your logs look very similar to Harry's in that it also shows the desired velocity and actual velocity diverging massively which is most likely a compass issue.  It looks like you did set your compass orientation to ROLL_180 which is the right value if you're using the 3dr gps+compass module.  If you're using the stand-alone compass then it depends how you mount it.

    3692838894?profile=original   The issue was not compass interference (at least according to the tlog of the previous flight).  The interference looks quite low vs throttle.  3692838996?profile=originalI see your point about more failsafes when things seem to be going horribly wrong.  We have GPS glitch protection coming in AC3.1 which will hopefully reduce the fly-aways caused by GPS problems but wouldn't help in your (or Harry's) case.  Some kind of check of the desired velocity vs actual velocity is possible so I'll look into that and chat about it with the dev team.  Thanks for the suggestion and sorry for your troubles.

  • Same thing appears to be happening to a lot of people...RTL and LOITER are making the aircraft pitch violently in one direction (mostly seems to the right and away from the pilot), go to high throttle, and fly into the ground at a steep angle.

    Happened to me 3 times today...last time in fatal crash.

  • So, after a lot more reading, I finally understand one important item I was missing.

    To recover from a failsafe RTL event, THE APM MUST SEE YOU SWITCH TO ANOTHER MODE. 

    Although I remember this now that I re-read it, I completely forgot about it until now.

    I believed I had a complete loss of control, but the fact is the copter ignored my inputs because it was doing what it was programmed to do. It was my lack of completing the setup that caused RTL to fail.

    So all that is a mystery now is why the radio failsafe to begin with. 

    I have rebuilt the quad and completed setup now. I also added the Rssi monitoring circuit for the rx.

    I flew today and had excellent loiter, auto, RTL, and stabilize modes. I tested radio failsafe by switching off transmitter and that worked well.

    I flew over 4 times farther away and my rxrssi signal never dropped below about 35% actual. I was able to get it down to about 25% by placing the transmitter behind my metal truck utility bed box. At what point does the FRsky receiver go in to failsafe?

    Any input is appreciated,


  • I've just had a crash that looks very similar to this: RTL went "crazy" resulting in full pitch and throttle being given resulting in the quad flying at top speed into the ground.

    I've posted about it here with my log. Here's the bit from your log that looks really similar to what happened to me. 

    3692828262?profile=originalYou say you hadn't finished setup. I've spent a lot of time setting mine up. The previous time I flew two days ago it was working brilliantly with good loiter even in strong wind. I didn't change anything from then until this final flight. I don't have any wifi things on board. So I'm not sure that any of those things are your problem either. 

    I don't know what is up though. It's depressing.


  • Also, can someone please look at my logs and tell me the exact "Home" Lat, Long, and Alt.

    When I first powered mission planner back on, it showed my home location as the crash site.

    I don't understand how it could have been saved as home.



  • So I hooked up the RSSI output to the apm via input A1. I used an rc lowpass filter per the FRsky documentation.

    The voltage from the FRsky is only a max of 3 volts with a full/strong signal(as expected).

    Mission planner "rxrssi" shows approx 60% at full signal(also as expected due to 0v to 5v scaling)

    I performed a range test to check the signal strength. Outdoors minimum obstructions.

    At about 50 feet away, my "rxrssi" drops to about 35% indicated (=approx 60%of full signal value) with the antenna pointed directly at the receiver. Somewhat higher with antenna point vertically.

    I then performed the same tests with the Gopro wifi on. No significant difference was noticed. I tried putting the gopro right next to the receiver with no noticable drop in RSSI.

    Still working on finding the cause of the failsafe.



  • Hello John.
    Simply put, I had no intentions of using any mode other than STABILIZE.
    Steps that where complete are limited to:
    Performed IMU calibration by placing copter in each of the 6 positions requested.
    Performed ESC calibrations
    Performed Radio Calibration

    Items not done:
    Did not perform Compassmot
    Did not perform compass auto declination
    I am not positive the external compass was mounted correctly. Althought it did match my cell phone compass reading reasonably well at rest.

    Stabilize was, well, Stable. It handled the wind with no issues.
    My biggest mistake other than flying it this way was the fact that I had Radio failsafe enabled for an RTL.
    Thanks for your input,
  • I see from your notes that Telemetry was not connected. You leave a lot to the imagination with the statement, "I know the setup was incomplete on this quad.".

    Could you elaborate on what setup or additional setup steps were yet to do?

    Doing so may yield more answers for you regarding the failure.


  • Any chance the GoPro WiFi signal interfered with your transmitter?
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