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  1. #11
    Hostage Taker of Quads Craftydan's Avatar
    Join Date
    May 2013
    Location
    Middle Ga
    Posts
    7,464
    Quote Originally Posted by arslanwali View Post
    thanks gazoo for the elaborative answer.yup, calibrated the ESC.
    yeah, that's what I was wondering, that in case of a winding breakage the motor stutters (that's what I've read on different forms, pardon my limited knowledge if there's more to it), but this motor spins smoothly, the rpm seemed to have dropped significantly, hence the decrease in thrust. I checked, the shaft moves freely when it's powered on with a lipo or when I spin it with hand. It doesn't even get hot when it's powered on with a lipo. I was wondering, since it seems to be having a low rpm now, what would happen if I put on a much bigger prop, could be tried?
    how can I make sure that it's the magnet failure which is causing this problem?
    So from the symptoms . . .

    You're saying the heat is well managed, and the kv appears to have droped. That means the motor isn't overloaded with the current prop (which would be a good load for a stock beef on 3S). kV is inversly proportional to the number of windings, so shoring a coil would increase the motors kV -- either the motor would spin FASTER with a partially shorted coil, or would bog down under the new desire to spin the prop faster and overheat.

    Your coils are fine. Smooth run with no stutter means no break. No overheat and slower spin at WOT ( on different escs) means no shorts.

    You're left with

    - magnets loosing pull
    - lower voltage battery or excessive voltage sag at WOT
    - the escs are both being told something less than WOT from the radio gear when the trottle stic is all the way up.

    Without having something to compare it against (another beef motor) there aren't good measures of magnetic strength that would aid in troubleshooting. This is something you'd diagnose from the symptoms by eliminating everything else.
    Crafty Dan
    -<-' ~~~
    __________________________________________________
    What goes up, must be smashed into little pieces (eventually)

  2. #12
    Old and Bold RC PILOT
    Join Date
    Aug 2016
    Location
    Brisbane, Australia
    Posts
    1,811
    Just a note!

    A shorted turn in any electrical motor will not cause an increase in speed but rather a loss of efficiency and extra heat generated.

    In a sensorless brushless system the effect of a short is to produce eddy currents in the shorted turn/s which oppose the magnet field generated by the applied waveform from the speed controller. Where the maximum power available is limited, (overcurrent protection), the loss of power due to the eddy currents generated in the shorted turns can produce heating and or other effects.

    Most sensorless motor speed speed controllers use back EMF and inductance effects to determine the required waveform to be generated. Where the FEEDBACK mechanism, (back EMF and inductance) is effected the resultant effect upon the operation of the motor can range from complete failure to operate, through stuttering, to slow rotation, (effectively reduced Kv), rotational speed plateau, and even engine fire.

    The reference to shorted turn is used to generalise a series of different types of winding short and leakage conditions for simplicity. The types of shorts can be a single turn in a single pole through to phase to phase shorts and or leakage. The reference to a winding is to included all poles of the motor connected to a single phase from the motor speed controller.

    Simple fault finding would tell where the fault lays. If you substitute the ESC or Battery and it makes not difference then they are eliminated as a cause. If swapping out the motor fixes the problem then the motor is definitely the issue.

    If the motor is complete, (no missing parts including magnets) and it rotates freely under hand turning then there is only two remaining items to suspect. Either the windings have a fault or the magnets have either gained or lost magnetism. As for the appearance of the windings you are only able to examine a small percentage of the motor windings and most motor winding to winding problems occur where heat is at its highest and cooling air reach is least and this is in the middle section of the coli/s. Without resorting to some serious test equipment capable of measuring inductance and reluctance the generator test is the cheapest and most accurate method of measuring the efficiency, (relative - comparing the other windings), of the three windings in a permanent magnet 3 phase brushless motor.

    Where an ESC, (sensorless motor speed controller), has a current limiting or similar protection mechanism the only real method of protection apart from load disconnection is to reduce output current to avoid damage including from overheating. The reduction in current can take the form of even a reduction in throttle output, (and hence motor speed), in some Speed controllers in a similar manner to the "Soft" voltage cutoff on some motor speed controllers.

    Just as I was taught!

    Have fun!
    Hopefully making a difference!

  3. #13

    Join Date
    Mar 2016
    Location
    Pakistan
    Posts
    47
    checked with my friend, the beef went haywire after having a serious impact with the ground. he was flying the ft storch, 10*4.7 prop, 3s 2200 mAh lipo. he was flying at a low altitude, was trying some moves, lost control and the plane hit the ground nose first. it was a tarmack, not a soft ground. the additional prop adapter that comes with the beef bent slightly so it must've been a hard impact. the motor started giving problems right after this incident. visually the motor seemed fine at that time and wasn't hot hot. my guess, winding issue. I still need to check it with an ohm meter, have national holidays here, will do so in the coming week.

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