Quadcopter flips on liftoff


I've seen multiple threads about this topic and have tried most (if not all) documented fixes for this problem.

I build a quadcopter using these parts:

Pixhawk Advanced AutopilotUblox Neo-7M GPS with Compass (not connected)DT750 Hextronic Outrunner 750kvRotorBits QuadCopter Kit With Modular Assembly SystemProps 2pc CW 2 pc CCW Rotation 12" 4.5 pitchCompact 4000mAh 3S 25C Lipo PackAfro ESC 20Amp Multi-rotor Motor Speed ControllerPPM encoder for PWM signal from the 5ch RC controller


From the threads i've gone through, i have:

  • Made sure that the proper motors are attached to pixhawk in the proper manner (shown in the picture).
  • Made sure that the propellers were spinning in the right direction.
  • Made sure that the clockwise and counter clockwise props are on the right motors (seen in the picture).
  • calibrated the accelerometer in mission planner. Values given when on flat ground is

Pitch: (±0.01 - 0.2). Roll: (±0.01-0.4).

  • Ran motor test to see if vibrations/battery affect accelerometer. They do not.
  • tested over grass and flat concrete.
  • Started with Arducopter 3.01, upgraded to 3.2 to see if the problem might be fixed.
  • Radio gives proper outputs and was calibrated.
  • ESC's are calibrated.
  • Made sure it was in + configuration.
  • Ran motor tests.

A couple of comments about the quad:

  • The pixhawk is not centered on the base, its a little off (towards the back towards motor #4).
  • The weight is pretty well distributed but not perfect.
  • starts flipping at about 50% throttle.
  • always flips towards the corner (between 2 arms, could this mean that there is extra pitch and roll?)
  • using 5 channel controller and a ppm encoder for rc. All channels work (1-5) properly.
  • I have logs, no idea how they work but i just downloaded them from the pixhawk using mavlink.

I've tried fixing this problem for 2 weeks but i cannot find anything wrong with the quad. I've looked at multiple forums and all the solutions were not applicable to my quad (usually configuration problem with props/motors). I'd love some help or any suggestions. 

Thank you.

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  • Need the logs for this problem.  It will tell us how the flight controller is responding to the takeoff.  It will tell us which motor is being powered and what the flight controller thinks is happening.


    • I don't know if these are the right files.

      2014-11-29 18-52-20 15.bin.log

      2014-11-29 18-52-19 14.bin.log

      • Both these files show motor 3 is running hot and that your RCIN are all at zero.  They should be at 1000-2000.

        For example at mid stick or Pitch and Roll at takeoff should be at 1500 for center.

        Don't know how your getting the unit to takeoff.




        • Here is a more recent log of this morning. RCIN values are looking normal now, i do not know why they weren't there before.

          2014-12-01 11-15-12 1.bin.log

          • I also noticed that the roll is off by 0.4 and pitch is off by 0.15. I tried to do the calibration multiple times but could not figured out how to do it perfectly.

        • I tried looking at the logs and the RCIN's are all 0 (don't know why). RCOUT has values that look like what my quad is receiving.

          The min for my rc controller is 975 and the max is 1980. I made sure to make sure all sticks were at their mid (except throttle which was at 975). I don't know why the RCIN values are all 0 as the quad was obviously responding to throttle.

          For motor 3 running hot, I did notice that one of the motors, when spun with the hand, had a little more resistance in its spin. When i start up all the engines, it looks like it spins the same speed as all the others.

  • Add-on to my previous post:

    If the PDB is wired correctly but facing 180 degrees in the wrong direction, you will get the same flip-over problem. (If 90 degrees off, severe instability and crash on take-off).


    • For the quad, we are using a simple breakout cable. I don't think this could cause the problem.

      As for controls, the flips occur with only throttle. Even after assuring that the sticks were centered with calibrating the rc inputs and calculating their median value and making sure not to change them.

      • Ok (no PDB);

        Though it wasn't actually the battery-to-ESC (power) connection I was worried about (your second picture).

        It's the Controller-to-ESC signal connections I'd still suspect first.

        I can't see those connections in your picture. How are you connecting the ESCs to the flight controller?

        To be sure everything's wired correctly, some people suggest holding the quad (very carefully) above your head and, with mid-power to motors, apply pitch and roll on the transmitter and see if the quad wants to tilt in the expected directions. If not (if opposite to expected directions), the output connections from the controller are going to the wrong ESCs/motors (or your transmitter controls are 'reversed', but unlikely since you're not touching pitch/roll during the flips).

        More safely (my choice), with quad on the ground as usual, don't give enough throttle to lift off - just 25% or so - and in short, quick bursts, apply extra pitch in one direction then the other, then the same for extra roll. If the quad 'tilts' in all four directions the way it should, it's not a wiring problem.

        My advice is don't assume it can't be a wiring problem - check.



        • I checked the Motor configuration but I did not do a hand test. I will check the motor configuration again and  perform the test on monday (Quad is not with me). Thank you.

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