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Motor (ESC) failure in flight!

Discussion in 'Cinestar 8' started by Steve Maller, Sep 18, 2013.

  1. Steve Maller

    Steve Maller UAV Grief Counselor

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    Beautiful morning here, and I wanted to capture a few still photos of the coastline. Took the Cinestar down to the beach, and, after my customary preflight, took off from the cliff and headed out over the waves. As I climbed to about 60m (about 70m above sea level), Frau Graupner implored "Motor Failure", something which I'd never heard. And sure enough, I could sort of make out motor #3 slowly spinning to a halt. As my heart sank and all my body hair all of a sudden stood at attention rather abruptly, I slowly inventoried the situation.
    1. I still seemed to have control of the copter, which was perfectly stable (AH was on).
    2. I was nose in, so I slowly brought her back over the sand first (haven't perfected ocean landings yet) making sure I didn't do anything abrupt.
    3. Once I was safely back over land, I started descending and heading back toward my takeoff spot, appealing to all deities who I could recall from Comparative Religions 117.
    4. I finally turned off AH, not wanting to land with anything automatic running.
    5. Turned her around, and landed uneventfully, with one prop dead still. AMAZING.
    So what happened? I'm not sure how, but Brushless controller #3 bit the dust. I unplugged everything after it landed, then reconnected one of the LiPos, and sure enough, got a loud POP from BL #3. My theory is that something got onto the PDB and shorted something out, but maybe one of the caps just bit the dust. I'm not sure. I'll know more when I disassemble everything.
    But man, I am singing the praises of redundant motors and a well-programmed Flight Control board. Thank you, Holger. o_O
    GPX file attached for your entertainment. Empty your bladder before replaying it.
    Parallels Desktop-snap001.jpg
     

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  2. Brad Meier

    Brad Meier Active Member
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    Ive had that happen also, a few times, both due to MK controllers. First was with my CS8 3axis with 7D on it. Took off and a motor shut down. Never got above 5 ft and never noticed and change in flight... just had a motor not spinning. Landed and restarted fine. Haven't had a problem since.

    Second time was with an older hexa that lost a motor in altitude hold. I only had a GoPro mounted so it was fairly light. This is where you got lucky. Mine immediately went into a slow spin. It was trying to maintain altitude while coping with the loss of a motor. Spinning was a result of not enough power from the other 2 working motors to counteract the opposite spinning 3 motors and be able to maintain altitude.

    I think your CS8 handled it ok because you had 7 motors vs my 5. Lesson is... turn off automation if things aren't going well for you. Chances are, as in my case, automation is working against you.
     
  3. Steve Maller

    Steve Maller UAV Grief Counselor

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    FYI, here are the stills that the GH3 took during the flight. Still shaking a bit (me, not the camera). :confused:

     
  4. Tyler Olson

    Tyler Olson Member

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    I had a motor drop out the other day as well flying with the 5D. I also had a poor compass calibration so it was a bit hard to control but managed to bring it back home and land it OK. Agreed- well designed machine and I was very thankful for the redundancy.
     
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  5. Casey Van Nyhuis

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    Are you planning to replace the whole BL or are you going to try just replacing the caps first?
     
  6. Scott Stemm

    Scott Stemm Member

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    Sounds like he's going to change something first but I don't think it's on the octa :)
     
  7. Steve Maller

    Steve Maller UAV Grief Counselor

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    Casey, I think after hearing and seeing the minor explosion on the board, I'd feel better replacing the whole BL. How hard is that? I'd rate my soldering skill a 'B' or so.
     
  8. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    A cap blowing can make a very loud noise, Steve. I'd suggest you replace the caps and ground test the BL #3 while it is still on the PDB. If you get a solid green LED on the BL-Ctrl, then try a low-altitude hover -- or just run up the engines with the props removed. If you don't get the green light, then you're out the cap and the time to replace it, but you will, of course, have to strip the bird and do the BL-Ctrl replacement thing....

    Then thank the assorted deities to which you refer for giving you the wisdom to choose an octocopter.....there is, as you discovered for us, sufficient control authority with seven motors to still maintain controlled flight. You may wish to also thank the deities that only your underwear and your ego were affected by this "character-building" moment.....

    Andy.
     
  9. Steve Maller

    Steve Maller UAV Grief Counselor

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    The caps looked ok, but one of the mosfets (?) looks busted, and the board has some noticeable scarring.
    image.jpg image.jpg
     
  10. Gary Haynes

    Gary Haynes Administrator
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    That should be an easy repair if it is only the MOSFET. I don't see anything else that looks damaged.
     
  11. Gustavo Rios

    Gustavo Rios Member

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    Steve, you also have a burned smd.
     

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  12. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    That ain't a cap that blew. New BL-Ctril. No contest. (Nolo contendere for Latin speakers).
    Wonder why that MOSFET decided it didn't want to be a MOSFET?

    Andy.
     
  13. Steve Maller

    Steve Maller UAV Grief Counselor

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    It also appears as though my PDB in general is quite dirty. Any thoughts as to how I could clean it periodically? I fly in pretty dirty surroundings (I guess most of us do), and I know the rotors are kicking up all kinds of debris. I suspect that something conductive was possibly the cause of a short (?) that resulted in the BL frying.
     
  14. Casey Van Nyhuis

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    Ya i'd say without a doubt replace it completely. Even if you do replace all the things that look toasty there is no telling what else is damaged. It's certainly not fun to replace a BL though. JUST TAKE YOUR TIME AND DON"T FORCE IT!!! Usually people try to rip it off to fast and tear the solder pad off of the distribution ring and then you have to replace the whole ring....it's not fun! Somebody jump in and confirm but my young eyes spot a small strand of copper wire in the second picture around where the mounting hole is. That would be plenty to cause the issues you saw. If your not totally confident doing it yourself you can always send it in to Riley here at QC.
     
  15. Steve Maller

    Steve Maller UAV Grief Counselor

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    I went ahead and ordered a couple of spare BL-CTRLs, but after removing the busted one from my PDB, I think I may go ahead and send it in to Riley with the new BL and let him do it. Looks like I may not have the skills and correct soldering tip to do this, and it's not worth ruining my PDB ring. Thanks!

    Any thoughts as to the cleaning of a PDB?
     
  16. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I would use isopropyl alcohol sparingly to clean it. But test a small patch first with a Q-Tip -- it may remove the conformal coating. If all is well, I'd use a small paint brush rather than a Q-Tip -- the Q-Tip sheds lots of little white fibers.

    Was that a small wire around the mounting hole or are you moulting again, Steve? :)

    Casey's words are spot on when it comes to BL-Ctrl replacement. The problem is that the capacitor leads are used as the structural mounting too and it takes some patience, a solder sucker, and some desoldering braid, to get the solder off to release the defunct BL-Ctrl. Rush it/force it/fail to use enough desoldering foreplay, and you'll trash the PDB.

    It's more tedious and requiring patience than it is difficult. I believe Dave King has replaced a BL-Ctrl too. Comments, Dave?

    Andy
     
  17. Elliott Dunwody

    Elliott Dunwody New Member

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    Can't reply on the tech stuff but congratulations on bringing her in with a broken wing.
    That's some mighty cold water to be swimming in.

    E
     
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  18. Steve Maller

    Steve Maller UAV Grief Counselor

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    Yeah, I've watched a lot of old war movies.
    Imagining bringing in a B-17 with engine #1 on fire.
    But that's my imagination.
    It wasn't at all that exciting. :rolleyes:
     
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  19. Dave King

    Dave King Well-Known Member

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    Sorry to hear. I"m actually doing to do a video on replacing a BL next week. It's not as hard as you think. You just have to take your time.
     
  20. Steve Maller

    Steve Maller UAV Grief Counselor

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    I have a replacement PDB arriving any day now, so I'll give the soldering a shot with my current one.
    Dave, let me know when your video is up. I look forward to it...thank you for doing it!!!
     

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