Hi All,

This is the first miss behaviour I have had from my Quad in almost a year.  I was tuning the quad though ch6.  Rate P was what I was interested in.


I landed the quad and heard the motors fire then stop.  I was just about to take off again when the quad took off on its own.  Reviewing the logs as it did so was a mode change to RTL.  I don't have RTL setup.


The quad is pretty stuffed and requires a complete rebuild including a replacement frame, landing gear and gimbal.


Could someone look at the logs attached and let me know why it decided RTL was a good idea?


CH5 is my mode change by the way.


Quad always flown on Stabilize.




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     Craig and I had a look at your logs and we've found the problem.   It appears that the THR_FS_VALUE parameter was set very high and dangerously close to your RC3_MIN.  Normally the THR_FS_VALUE parameter is set to about 975 and when your throttle drops below this value, the APM2 will register a failsafe event and move into RTL mode.


     In this case, this THR_FS_VALUE was set to 1045 but that is only 2 PWM values below you throttle minimum throttle.  PWM values can certainly move around a few points so in this case when you held your throttle low it momentarily dropped to 1043 and the failsafe was triggered and the APM when into RTL mode.

Hi Guys,

I woke up this morning and realised that I had not full understood the failsafe setup.  Your post confirms my suspicion.


Thanks Guys,


Hi Guys,


I was able to duplicate the fault last night.  Well, not actually a fault, ebkak or ID10T.  Anyway, I spent the whole of last night rebuilding my quad.  I got it tuned to the point of stabilize and Alt hold, so a little further, however I had another failure.


I suspect that a motor mount failed, which was perhaps already fractured.  Nothing obvious in the rebuild cropped up though.  I am a veteran rc heli pilot so have the methodical nature to touch and put pressure on all parts all the time to check that everything is in order.


Please see the attached log file and let me know if it looks like the front left motor mount failed.  It litterally just snapped off.


One final note that might assist you is the quadcopter had a slow yaw drift.  I figured it was just settling in as it has done in the past.






     Something very bad happens but it's hard to be sure what.  below you can see a graph of the output of the 4 motors on the right side go very high, two on the left go very low.  If you hadn't said it was a motor mount that failed on teh front left..I'd say it was more likely a failure on one of the right side engines (motors 1 or 4).

     But you know..if you've got a piece of broken motor mount in your hands, I'm going with that as the cause of your troubles. :-).

     By the way, what I'm doing is actually possible for anyone to do:

      1. open mission planner's flight data screen

      2. at the bottom left select the Telemetry Logs tab

      3. click "Tlog > Kml or Graph"

      4. when the "log" window pops up select "Graph Log" and Open the tlog file that you attached above

      5. after it loads, a massive list of possible fields will appear..select "servo1_raw", "servo2_raw", "servo3_raw" and "servo4_raw" to graph the pwms being sent to each motor.

Hey Randy,

Its very plausible. I appreciate the tip on the log graph, I hate other people doing the work for me.  MUCH appriciation on your rapid responses.


Have a great day!


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