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Mid flight motor failure

Discussion in 'Phantom 1 Help' started by zaheed, Sep 1, 2013.

  1. zaheed

    Aug 31, 2013
    Likes Received:

    The front right motor (M1) of my phantom stopped working barely 30 secs into my first flight for today, and made it crash. Fortunately it was just couple of meters above grassy field so there were no damages except the Zenmuse gimbal dampers came off and the first prop to hit the ground got some scratches. I'm using carbon fiber 8x4.5 props, I should probably throw away that prop, or is it okay to use props with slightly rough/scratchy edges? The problem is I've another set of same-spec/kind of props but from a different source. They look the same but I don't feel comfortable combining them, just in case they've slightly different properties.

    Anyway coming back to the main issue, I should mention I had replaced the stock motors with T-Motor upgrades. But I've had several 7+ mins of successful flights after the replacement without any issues. Also, now the motor in question isn't completely dead. When I arm the motors, while the other 3 motors start running smoothly, this one keeps oscillating back and forth a bit, and does a full rotation every now and then. It seems as if the ESC don't get the feedback or can't compute the direction of the motor correctly. The ESC (red) light stays off but every 10-15 seconds it lights up and goes off quickly. I've tried swapping the ESC connection with M2 port on Naza and the result is the same - motor on M1 works fine, but this one now connected to M2 still only oscillates rather than spinning. Then I used my multimeter to compare the resistances between various points in the ESC of this motor and the other ESCs. I found at least one discrepancy where the resistance was 5 times less (~550 ohm vs ~100 ohm) in this one (FYI, polarity of leads were same when comparing). I also checked the obvious things like ESC connections to power supply and motor connections. At least as per the multimeter they are connected, but of course I can't test if the connections are good enough for required power draw during operation.

    So my conclusion thus far is the ESC is definitely misbehaving. This really worries me because it couldn't have got overheated in 30 secs of flight. It doesn't look fried - no visible difference with other ESCs. Even the led lights up once in a while. It shouldn't have got damaged because of higher current draw because T-motors are more efficient, if anything. I've ordered a replacement ESC, it's cheap so that doesn't worry me.

    BUT, what if this happened when I was at 50 meters over a concrete surface or river/lake? Are these ESCs expected to fail just like that for no good reason? This was probably my 20 something flight so it couldn't have come faulty from factory. Then how do I know the same failure won't happen to my replacement ESC?

    Also, is there anything else I should be testing before putting on the replacement so that I know the problem isn't somewhere else and I don't end up damaging the replacement too.

    Any input regarding this is highly appreciated, thanks in advance!
  2. bumper

    Aug 6, 2013
    Likes Received:
    I'm betting the problem is a bad ESC.

    I had one fail, though not with the same symptoms - my M1 motor intermittently would not run at all. Swapping plugs on NAZA had problem staying w/ same motor. ESC's are available on eBay in "red" and "green" for about $18 IIRC.