Crash after uncontrollable yaw- please help

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

  1. Manuel Frauendorf

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    Hey guys,

    I had a rather nasty experience with my CS 8. In the middle of a flight, the copter started to yaw fast and in a way which made it impossible for me to hold against with stick. Kept spinning, I believe to the right and did not stop again.
    Was not able to control the beast and had to try and land it spinning fast around it's own axle . It crashed with a 5 D mounted.

    Fortunately despite propellers and a broken landing gear leg of the 360 Gimbal nothing obvious was broken.
    More than the parts broken I'm a bit devastaded because I got no idea why it happened and will not be easy again on future flights with that copter until I find the reason and solve the problem.

    It was realy dangerous as it is almost impossible to make a controllable descent with the machine spinning like crazy. Luckily noone was in the way!

    Here some facts:

    CS 8 45mm booms
    MK electronics, during flight no gps or height control
    Compass value/ influence in MK toll set to ZERO
    Xoar 14x 6 props
    2x 5000, 4s lipos
    3 Axis Gimbal w/ radians
    5D mounted
    BL temperatures below 60 Celsius

    Would be thankful for any thoughts on what might have caused this weird behaviour.

    Manuel
     
  2. Tyler Olson

    Tyler Olson Member

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    scary stuff! Nothing like a flying guillotine to get the blood pumping. Hope someone can help
     
  3. Howard Dapp

    Howard Dapp Active Member

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    Sorry to hear and thankfully no major damage. Early on I've found that flight control is still influenced even if the compass and gps is turned off. I do not have the gps and compass boards installed at all...I don't trust them, one day they work great then the next day they have a mind of their own. Remove them and fly with confidence, you don't want some unexplained uncontrolled episode while on a gig in front of a client. Upload your gpx file and let someone try and offer a guess as to what happened.
     
  4. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Glad to hear that nobody was hurt and the damage was limited. As Howard says if you can upload your GPX file we might be able to analyze what happened. From what I have heard, with the CS8, even if you lose a prop/motor/BL controller, while there is yaw, you still have sufficient control authority to fly the aircraft -- therefore it sounds like something pretty serious (and more serious than a single motor out) has happened.

    Did you see any kind of odd behavior before this sudden yawing?
    Had you re-calibrated your compass recently? (I do not mean do imply that you should have -- just trying to understand.)
    Can you tell us anything about the environment in which you were flying? Were there any Wifi nodes, cell phone towers, power lines, etc. in the immediate area?

    I'm sure other folks will have other questions, but many of those get answered by the GPX file.

    Thanks
    Andy.
     
  5. Manuel Frauendorf

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    Unfortunately I have not logged the flight as I had the card in another system which I test- wish I would have logged!!!!

    To give some more deatail anyways:
    I was descending from about 50 m it occured at about 15 m above ground. Wind: It was a calm day day even though flying at a corner of a building it was more wind than at the place I was standing.

    Wifi or phone towers: There was indeed a mobile phone tower near by, but not really close: about 200-300 m away.
    Strange thing is, that my cameraoperator noticed a picture signal drop at a previous flight at exactly the place where yaw problem occured. But when testing the signal later after the crash by hand (took the copter and walked to the same place) it did not occur.

    Compass callibration: Due to frequent magnet error warnings days before, calibration was done before flight according to Holger Busses "New Method" in the open field.

    Another strange thing I noticed while watching-listening- to the crash video. The sound of the copter changed at point of yaw to a somehow squeeling high pitch noise among the usual bees nest humming which also seemed a bit "nervous" (as always the case when doing a faster descent).

    I'm on an assignment trip this week , as soon as I get back home I will upload the video for you. Due to the automatic pan one can not see the yaw in the video at all, as the pan radian effectively kept the frame even though the multirotor above was doing crazy stuff.
     
  6. Dave King

    Dave King Well-Known Member

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    Manuel

    Sorry to hear about this. I'm not sure if this will help but I will share my somewhat similar experience I had. I was in the middle of filming one day and some how in between flights I had a situation where the copter was yawing slowly but was controllable if I had used the stick with a hard right. I landed and checked everything, everything seemed good. Then I hooked up MK tools to the kopter and looked at the channels tab where I saw my yaw channel was about 25% higher than where it should be at the center position. I tried to recalibrate the stick position through the MX20 but it didn't help. The only thing that worked was for me to start a new program on the MX20 and load all my settings into the program one at a a time. This fixed it for me.
     
  7. Manuel Frauendorf

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    Thanx dave for your comment, I think this is not my problem. On flights with different copters after that the problem did not occur.
    Also my yaw was quite fast. Good that you had enough stick travel available to yaw against when it happened:)
     
  8. William Johnston

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    It sounds like the gyro on flight controller failed. Is your CS8 still doing this or was it a one time event?
     
  9. Dave King

    Dave King Well-Known Member

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    HI Manuel

    You might want to verify that the yaw channel in MK tools is 0 in the center position just to eliminate that element.
     
  10. Manuel Frauendorf

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    Yaw channel in MK tool: can check that as soon as I get back to berlin and the copter (on monday)then I could also check if it still does the yaw...
     
  11. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    I'm wondering what that high pitched alarm sound was, Manuel. That is something that might be worth investigating. Was it the buzzer on the copter beeping or sounding continuously?

    Andy.
     
  12. Manuel Frauendorf

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    The hight pitch sound was not the buzzer, think it was coming from an engine..
     
  13. Stefan Hunziker

    Stefan Hunziker New Member

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    hello manuel
    i had a similar problem 2 years ago with one of my copters (NOT A CINESTAR...) . the reason was that one of the propeller screws was not tightened enough and the prop was slipping on the motor axis. as the thrust of this motor is then not strong enough, the rpm rise which causes this high pitch engine noise and the copter spins around its axis. i was able to land with no damage, but that was more luck than control.... hope this helps
    stefan

    p.s. since that incident, i check the props before every flight......
     
  14. Manuel Frauendorf

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    Just wanted to share some findings:

    - changed bearings in 3 engines KW8
    - New FC 2.2 as i suspected that the ACC might be damaged, latest Software-updates on FC and NC
    - props balanced again
    - ACC calibrated
    - compass value on zero
    - checked yaw stick input setting- no expo or anything
    - mounted FC much higher, NC and GPS is mounted on one boom

    Result:still yaws to the left upon liftoff no control, hard to land

    Any ideas???
     
  15. Manuel Frauendorf

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    By the way, checked the gyro stick, it is at zero!
     
  16. Manuel Frauendorf

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    Sorry, mean the yaw- stick
     
  17. Gary Haynes

    Gary Haynes Administrator
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    Manuel I would carefully check each motor and prop for proper rotation and prop type (CW/CCW). You can check motor rotation using the motor control function in the MKTool where you can run each motor individually. Just don't run the throttle up very high? Also have you checked that the the motors are all vertical? This is just a shot in the dark since it sounds like it had been flying ok and something changed.
     
  18. Dave King

    Dave King Well-Known Member

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    Gary has good ideas. Did you check the Yaw channel in MK tool?
     
  19. William Johnston

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    Did you replace the whole flight controller or just upgrade the accelerometer?
     
  20. Manuel Frauendorf

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    @gary: yes, checked the yaw channel-is zero when stick is in the middle AND: on engine was not perfectly vertical, fixed that and the slow yaw is gone, in addition I activated the compass again and set the value to 60--THANK YOU !;)
    @william: yes replaced the entire FC, did not want to do any soldering little pins myself

    BUT: Now I have a different issue:
    as you can see in gpx file one MK BL 2.0 is running very hot above 90 Degrees Celsius.
    It was a hot day at about 30 celsius but still it seems strange that only that one is having the temp. issue.

    How far can I go without damaging it or risking a crash?
     

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