Crash after uncontrollable yaw- please help

Discussion in 'Cinestar 8' started by Manuel Frauendorf, Jul 3, 2013.

  1. Gary Haynes

    Gary Haynes Administrator
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    Manuel getting closer. Do you have an Xbee wireless setup so that we could use MKTool while the copter is in flight? If so you can go into the 3D screens and see the actual balance of the copter. Might be that it is out of balance and one motor is working harder to compensate.

    Also I notice that your max battery voltage was only 15.3v. Doesn't look like the batteries were fully charged.

    Other things that could be checked are the bearings on the number 4 motor, swap number 4 with number 6 or 8 to see if it is a motor issue (would also help isolate the balance issue if you don't have a wireless setup).

    You didn't mention your total copter weight but you are seeing the effects of high ambient temps. Lots of hovering flight will also drive up temps since there is reduced airflow over the BL's.
     
  2. William Johnston

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    Once an ESC temperature gets to 100C it starts throttling back on the power to it's motor in order to save itself. If you have altitude hold on when this happens your copter will start to fly off in the direction of the over heating ESC. If you have only position hold on it will do a nice job of landing itself.

    Anyway, it looks like your CS8 is heavy towards motor 4. Try balancing the CS8. You should be able to pick it up by any two opposite booms and not have it tilt.

    Also, it looks to me like your CS8 has a clockwise moment to it that makes your counter-clockwise motors work harder to make up for. (Either that or you were spinning the CS8) Make sure all your motors axes are orthogonal to the hub plane.

    It the combination of the two things that makes motor 4's average current be 15.0 amps while Motor 7's average current is only 5.0 amps.
     
  3. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    [Sorry -- my posting somewhat duplicates other responses -- sorry -- they didn't show up on my screen until I posted my response. Odd.]

    Manuel: Try swapping the "hot" motor to a different brushless controller -- swap it with a similar odd or even motor to avoid rotation direction issues.

    If you now see the motor in the new position making the BL-Ctrl run hot, then the problem is with the motor. If the "hot" motor stays in the same position, then the problem is with the BL-Ctrl. You might want to "re-flow" the solder joints on the BL-Control where the pig-tail wires with the bullet connectors attach to the BL-Ctrl board.

    Andy.
     
  4. Manuel Frauendorf

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    Thanks,
    Before I swap engines and check the bearings again I really wonder how it is possible that the clockwise turning engines need to work much harder than the counterclockwise motors. Means every other engine is hotter than its "neighbor"

    Seems the KW8 engines have lots of problems with their bearings. On engine 4 I already changed them. On my AXI engines I never had to change a bearing yet!

    Total weight was 7kg.
    The batteries were fully charged, just the flight was split in to parts. Uploaded only the second flight, when the batteries were a bit drained already.

    The balance of the system seems fine!
     
  5. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Usually that asymmetry of power between all the Odds and all the Evens (motors, that is) is as a result of having to provide constant yaw correction -- and the most likely cause for that would be motors whose prop shafts are not vertical as far as I can tell.

    One technique I use to assess how well the motors are aligned is to hover the copter at eye level about two meters in front of me, put it on Position Hold, and then yaw the copter around slowly -- then I can see each "disc" formed by the props. It's surprisingly easy to see if one such disc is canted over with respect to the horizontal.

    Hope this helps
    Andy.
     
  6. Manuel Frauendorf

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    Ok, thanks for the hint, all engines seem straight but obviously are not :)
    I'll try some other way: hang the copter by a rope and single run each engine with mk tool. If its perfectly vertical there should not remain any side movement of the copter lets see if that helps
     
  7. Manuel Frauendorf

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    It helped!
    So it is not a problem withthe engine or bl. But i stillsee a very big temperature gap of up to 40 deg. Celsius. Do you experience the same?
     
  8. Gary Haynes

    Gary Haynes Administrator
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    Manuel you might have a motor that is just not up to spec. I would shoot a message to Kopterworx and see if they will exchange it for you.
     

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