APM 2.6 / S550 Sudden Crash

Hello, I am running an S550 frame with APM 2.6 with external compass/GPS which has been flying without any real problems for a few months now. Yesterday I took it out and had a flight around the field behind my house, no problems and everything stable even though it was a little windy. Later on that evening I decided to take it out again as the wind had dropped, just basic stuff, hovering and flying slowly around the field. After approx 9 mins I was about to call it a day (low battery had not sounded yet) and come in to land when it suddenly flipped over and tumbled to the ground from around 30m totally destroying the frame. Unfortunately as I had only nipped out for a quick flight I didn't have my ground station running so no telemetry logs. I did however manage to download the log directly off the AMP. Most of the flight was in loiter mode, wind was fairly calm apart for the odd little gust, I wasn't pushing it anywhere near its limits and the battery voltage when I recovered it was 15.2v, also all the wiring was intact. So I cannot understand why this would happen but a similar thing happened a couple off weeks ago almost in the same place but at a much lower altitude resulting in a broken arm and prop.

Here is a link to the video https://youtu.be/fRwoSVDlyEI

Does anyone have any suggestions as to what could be casing it? I have just ordered a new frame but I am reluctant to fly it again until I get to the cause. 

Log files are also attached. 


S550 Hexacopter Frame
EMAX 2216 810kv Motors with 1045 props
Hobbywing XRotor 40A ESC's
Zippy 4s 5000mA 35C Lipo
APM 2.6 with GPS and AMP Power Module 
FlySky TH9X 9 Channel Radio
433Mhz MavLink Telemetry Radio
SJ4000 Wifi Camera 
Sony 1/3 CCD Flight Camera
5.8Ghz 600mW Boscam FPV Transmitter with circular polarised antenna
Turnigy Aircraft LED kit

2015-05-17 20-57-32.log

2015-05-17 20-57-32.bin

2015-05-17 20-57-32.kmz

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  • All you had to do was analyze your log data.  Right before it flipped at around 9 minutes mark in your log, you had RAD:RSSI spiked to over 120, RAD:RemNoise spiked to 60, RAD:RxErrors = 1, CURR:CurrTot dropped to zero and CURR:ThrInt dropped to zero.  Obvious sign of Radio communication lost.  So check your parameters....  Why would you disable your Failsafe?  In your PARM, FS_THR_ENABLE= 0 which is clearly disabled.  If it was enabled, RTL would have kicked in and you had good GPS locking so it would have come back to you.  Sorry for your lost, but that's clearly your own fault.

    • Yes, I don't know what I was thinking! No signal no input to the APM. Now I will definitely be using a preflight checklist in future and much further reading on the Arducopter site. Thanks for the info, at least now I know what happened and more importantly why. The good thing about DIY build is even in a crash like that which totally destroyed the frame it's only £30-40 to repair and I'll put this down to a learning experience.
    • Thanks Vinnie, I am still fairly new to this and not familiar with reading the log files, i will now read up on the full parm list! and yes it seems your right, i just plugged the AMP back in to mission planner and radio failsafe is indeed disabled. Don't know how thats happened as it was set up correctly when i last checked maybe I have changed it by mistake. A costly mistake I don't intend to make again... One question though... if i was in loiter mode and the radio signal failed for whatever reason would the GPS loiter not keep the copter stable? 

    • This is the tricky part.  APM will do only what it was instructed to do.  In Loiter, you still need throttle PWM to hold, but since the lost of radio resulted in throttle PWM dropping to zero, below the mid throttle threshold, APM would not do anything to compensate and that is why we need the failsafe.  Read up on how Alt Hold works.  In Loiter mode, Alt Hold functionality is shared to keep it stable.  Pay attention the half way down the page "Control" and understand the threshold of 40~60% throttle and outside the threshold means you want to descend. http://copter.ardupilot.com/wiki/flying-arducopter/flight-modes/alt...

  • It looked like all the motors on one side of the craft quit at the same time.

    Not trying to overthink this, but could have the motor / servo leads come off during flight?

  • Are you using a Go-pro to record the video?  I had an issue were the Go pro 2.4 wireless signal interfered with the 2.4 RC receiver.  If you are using a Go-pro make sure you turn off the WiFi.   I also had an issue with the latest code and went back to 3.15 so that I can use the terminal mode to reset my APM.  I had crazy issues with the latest build as the quad had a mind of its own.  3.15 seems were I will stay since the 2.6 is end of life.  Will upgrade to pixhawk in the future.  

    • I am using an SJ4000 Wifi but I did not have the wifi active during flight and also the first time it did this was before I had the camera. Thanks for the info I will remember never to use the wifi. 

    • Do you have fail safe setup for lost of signal?  I have it setup to RTL. 

    • Yes radio failsafe is set to RTL and there is a geofence set at Alt 100m Radius 500m. When this happened the copter was only maybe 30m direct line of sight to me and the transmitter batteries were new that day. Its just really weird the first time was puzzling but just thought I had done something wrong, but each time there has been no warning signs and it was after it had already been flying without issue. 

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