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Motor or ESC failure - Inspire1 meets lake

Discussion in 'Inspire 1 Discussion' started by Ferdi, Jul 8, 2015.

  1. Ferdi

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    Hey guys, I'd like some feedback on this incident and the events leading up to it. Just curious as to what your opinions are and how you would've handled the situation.

    History:
    On 16 June we experienced a compass error and fly away. (I couldn't attend the shoot as I had other pressing work, so my business partner did the piloting. All MOD values were good at take-off so I advised against doing a compass cal.) Anyway, when he could not get the craft back he landed in a field. The landing was soft but the craft tipped over. The pilot did a CSC and stopped the motors. No visible damage anywhere.
    He then moved to the next location for the day. Here he did a fresh compass calibration, but upon take-off the the right rear motor stopped (or never started, pilot wasn't sure) and the craft tipped over.
    The following day the craft was inspected by a DJI supplier and all motors were running fine, even when applying resistance to the motors.
    On 24 June we did a test flight, flying very low for 17mins, then immediately measured the temperature of each motor using a laser temperature gauge. All motors were the same temp. We flew 3 more successful missions with no incident.
    (I've heard reports of pilots recovering their crashed Inspires with motors smoking and not having problems with the motors afterwards.)

    Incident:
    Then on Sunday morning 5 July 2015 I was flying over a lake when our Inspire 1 suddenly, and without warning fell out of the sky like a stone.
    From the footage it appears to pitch back and to the right, so I suspect that either the right rear motor or ESC failed.
    I was about 22m above my take-off spot (which was about 6m above the lake), flying west against the wind when the incident happened.
    I was able to recover the craft from the lake, but it had spent about 3 hour in approximately 3m of fresh water.
    All the props were still attached, but the gimbal had been torn off. We recovered that as well.


    Password: tmc2015

    Followup:
    With the Inspire dead, I decided to take it apart and have a "peek under the hood". I must confess I rather enjoyed taking the old girl apart. When opening the motors I found something interesting. The motors on the left side of the craft looks perfect, but the ones on the right both have blackened copper wiring, as if it had burnt (see attached photos). I wonder what could've caused the blackened copper wiring?

    Looking forward to your constructive comments and opinions. ;)

    Left Front Motor.jpg
    Left Rear Motor.jpg Right Front Motor.jpg Right Rear Motor.jpg
     
  2. mad in nc

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    Cant see the video....

    My guess motor is burned due to the result of to much current which burned coating off wire, again a "guess" but thats a lot of current to scorch the wires on the motor...

    Cause - FET overload on/ from ESC's? To much current? What version is yours?
     
  3. Ferdi

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    Thanks for that. To view the video copy the password tmc2015 and paste it in the video window and press watch. Should work.

    Not sure what FET overload is or what version you're referring to?

    Thanks!
     
  4. ajohnsonlaird

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    I have been doing some bench testing of some non-DJI motors and as part of that testing, I successfully burned out a couple of motors. They have exactly the same appearance -- the insulating lacquer on the wires has "toasted" (in every sense of the word). In my case, it was because the Arduino controller was commanding a higher throttle setting for the size of prop I was testing with -- resulting in the motor consuming too much power, getting too hot and then "the smoke came out of the wires." :)

    I think mad in nc is referring to "field effect transistors" (FET) that are used in the electronic speed controllers -- basically the speed controllers were commanding the motors to spin so hard/fast that they pulled so much current that the coils melted their insulation, and that caused the crash.

    The larger mystery, which I'm not experienced enough with the I1 to comment on, is what would have caused that "FET overload." Could it be that there was some damage done to those motors when your colleague had the tip over if he/she wasn't quite quick enough to execute the CSC to shut the motors down -- the motors would have been "stalled" because the props were against the ground? I defer to others with superior knowledge of the I1 on this.
     
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  5. Ferdi

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    Thanks for the detailed response ajohnsonaird! I appreciate it!

    I've never seen one, so it's good to know what a burnt-out motor looks like :oops:

    It's possible the motors were damaged by the tip-over (I wasn't there so I can't definitively say that the motors were shut down quickly after the tip-over). I'm curious though, cause they ran fine for 4 full flights. During 3 of those 4 flights I did occasionally run the motors at or near 100% throttle with no problems.
     
  6. Ferdi

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    I've heard that if the ESC fails a huge amount of current hits the motor. Does anyone know if that's true, and if so, could that have caused the burnt-out motors?
     
  7. Geoelectro

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    Yes. The FETs turn on and off at a high frequency. There are three "channels" timed in such a way to move the motor. Usually they are never always on, but pulsed on and off. If one shorts, then full power goes to the coils that FET is controlling. You will notice in the pictures that not all the coils are burned. It appears two of the three channels failed.

    You could put a replacement motor in and test it to see if it runs. A brief power up shouldn't damage the motor winding. However, this should be a very quick test. If you have a shorted FET, powering it up you can try turning the prop by hand. A shorted FET will make turning the prop harder than a normal working ESC/motor.

    Geo
     
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  8. ajohnsonlaird

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    Yeah -- I'd not toasted a motor before. As Geoelectro says, you can see that the coil sets (of which there are three) have burned symmetrically.

    I wonder whether the tipover started the problem by burning off the insulating lacquer on some of the turns of the coils and, when they shorted out, the problem got progressively worse? The odd aspect to all of this is that it's two motors on the same side of the aircraft that burned out. You mentioned that one day the right rear motor failed to start. Do you happen to know whether the original tip over stalled the motors on the right hand side? If that was the case, there may be a trail of evidence that connects things together.

    But the contradictory evidence is that the motors seemed to work OK without getting hotter than usual.

    I had a tip-over on my I1, and I've inspected the coils on all of the motors but (fortunately) do not see any "toasting." It's easy to shine a flashlight (that's torch for the Brits) into the motor bell and see the upper end of the coils.

    Have there been other incidents of electronic speed controlller (ESC) / Metal Oxide Field Effect Transistors (MOSFET) failures on the I1? I can see from other threads there has been the suspicion of such failures, but nothing definitive.

    Andy.
     
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  9. The Editor

    The Editor Moderator
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    Hi Andy, (sorry, still not had a chance to get over to Freefly!)

    There are VERY few reported incidents of motor and/or ESC failures on the Inspire platform.
    When the aircraft was designed DJI completely engineered a new propulsion system from the ground up.
    It is the first time (to my knowledge) that reverse emf braking has been used on a multi rotor - and boy do we know that works! :p
    From memory, I think the escs are running at about 800hz which is another first.
    I'm with you in that I think the tip over caused the initial high current draw whilst the motors were stalled, which burnt off the insulation. The rest was only a matter of time.

    As an aside the OP asked whether full throttle for long periods of time would cause an issue. The answer to that on the Inspires/E800 propulsion system would be no. It is over engineered for the platform and the AC has a payload capability of 3.4kg. It is only spinning 13 by 4.5 props on 3510 kv350's on a 6S so things are not exactly stretched.

    I genuinely believe in this case the damage was done at the tipover with time then not being on the motors side. :(
     
    #9 The Editor, Jul 9, 2015
    Last edited: Jul 9, 2015
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  10. Wormwood

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    I'll stick my neck out on this one with the Inspire falling as it did I believe you lost power to one side of the craft the side without the burnt copper. The burnt copper is from the thermal shock of the motors hitting the water causing the konformal coating to delaminate off the wire & then begin corroding. Furthermore 3hours in fresh water with electrolysis going on using the the motor wiring at the anode/cathode, would create the same effects. If you look at the particular windings you see they're all on the opposite sides, that's particular phase the motor was current at when it came to rest in the water. Other words, why didn't half the side of the motor windings corrode? Only the windings that were being excited where the ones that were corroded. The side that has no corrosion obviously has no power either, or nothing that would be electrically common to the other motors on the other side of the craft. Or you might In reference to the clean motors, there was no physical connection to close the circuit & began electrolysis on those motors, so I have to assume the electrical connection had to be broken before it entered the water.

    Any which way you look at the culprit for everything lies in the fact one side having corrosion & the other not.
     
  11. mdomeny

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    isn't this a warranty case???
    are you sending it in to have it checked??
     
  12. Ferdi

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    I'm not sure wether or not it classifies as a warranty case. To find out I have submitted all the details / video / reports to DJI for analysis. I've got my own suspicions as to what happened, but at this stage I wont say what those are as I'm curious as to what the community's (and DJI's) opinions are. ;)

    If she went down on land I would've sent her in, but since she went into the water, and DJI (quite rightly) does not repair water damage, I'm not planning on sending her in at this stage. I'll keep her for parts for my next bird once/if insurance pays out. In the mean time the P3 will have to step into the breach.
     
  13. Ferdi

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    Yes, if it was a faulty component I would expect DJI to treat it as a warranty case and replace the bird. That's up to them to determine though. If they need me to send her in I will. I'll just have to wait to hear what our friends at DJI has to say.
     
  14. sirnikolas

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    Good luck mate! I can't wait to hear what Dji say.
     
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  15. Ferdi

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    Me too! :D I'll let you guys know when I hear from them...
     
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  16. IIIDaemon

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    ...1st thing i'd check (and suspect) are the bearing(s)... even after a short time under water.. but checking them days later wont tell you much, they look at least 'Shielded' if Not 'Sealed', but... hey, good luck on finding replacements (mtr, esc.....)...
    .
    IIIDaemon
    www.GasRecovery.net
     
  17. The Editor

    The Editor Moderator
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    No problem getting bearings whatsoever - available anywhere.
    They are standard sized 6852Z Metal Shielded bearings available pretty much anywhere on the planet! They can also be known as 685ZZ or 6852ZR
    Standard dia: 5/11/5 (Bore 5mm, OD 11mm Width 5mm).
     
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  18. IIIDaemon

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    ...replacements (mtr, esc...)... who replace bearings in a burnt motor??? ( pssst... the original post was trying to determine the Cause of Failure or the what Might Have caused the craft to suddenly tumble out of the sky.. i was mearly wishing him Luck on finding 'Trustworthy, Reliable' Motor or ESC replacements, and YES i am also aware of Ebay)
    .
    IIIDaemon
    www.GasRecovery.net

    UNTITLED.jpg
     
    #18 IIIDaemon, Jul 11, 2015
    Last edited: Jul 11, 2015
  19. Ferdi

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    Any and all info is greatly appreciated. The more I can learn about the I1 the happier I am :D
    Losing a bird can be a lonely experience, so the good wishes of fellow pilots are also much appreciated.
    Thanks you lot!
     
  20. The Editor

    The Editor Moderator
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    Silly me!