Flies ok, then dips motor #4. Every Time.

I thought i would try autotune, but that uncovered deeper issues. now my copter takes off ok, flies around ok (with non-tuned stock PIDS), but then drops its motor number 4. Not a complete motor stop, but definitely a loss of power. (still a failure with respect to a flying machine)

this behavior is repeatable, and i have captured it in a short log file. I had imu and motors turned on, and I can see the number 4 motor goes to max. this tells me that the control is working, but the motor is not. (or maybe the esc?)

Sounds like a hardware issue, huh? I have checked power dist. continuity, no apparent shorts, esc and motor dont get hot, and pwm wires are intact all the way. How should I go about finding the source of the problem? Where should I start? and how can i really test it to find the faulty component? Can anyone with quadcopter wisdom share some of that?

2013-11-30 16-32 2.log

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  • I have made three posts in regards to my situation without a single response. What is the trick?

  • I am experiencing similar problems, but my problem is on motor 6 on a octocopter. Motor is the last one to start spinning on throttle up and since it is on the back side of the copter I have to add forward pitch to keep level. I ahve changed motors, new motors, swapped motors, and esc. This is a default setup with no mods to PIDS.

  • Have you checked your ESC settings? You may have accidentally set a high battery cutoff voltage for ESC #4, so when your batteries start to run low, that ESC is doing a soft cutoff (to try to prevent damaging the battery).

  • leonard:

    sorry, the one posted in OP is a short flight, but it captures the failure nicely. I didnt try autotune in the log posted in OP.

    The attached one here is my latest attempt at autotune. it completed, but i must have screwed up the saving procedure. Since it completed, and produced a tighter control, im pretty sure the autotune is working, and I am seeing a mechanical/electrical issue of some kind

    2013-11-30 16-08 1.log

  • Switch the motor to another position. If problem moves with motor, it's the motor. If not, next switch the ESC with another, and while you do that have a look at the ESC to power distribution board connections (maybe solder joints), if one of those is high resistance it could be making the ESC cut out. If switching the motor and then the ESC doesn't change anything, then the problem is further upstream somewhere.

  • Developer

    Hi Ted,

    There was no Autotune in that log so I can't tell you why it didn't save. Do you want to post the Autotune log?

    This definitely looks like a problem with your rear right motor/prop/esc. Maybe overheating or low voltage cutoff. It is hard to tell because you don't seem to have a current/voltage sensor.

  • Check the bearings on that motor.  If they are loose, "gritty" or noisy, replace them.  Brushless motors are very simple, but the bearings are definitely a weak link.

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