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CRASH! Graupner MC-20 with WKM

Discussion in 'Electronics' started by Bryan Harvey, Feb 13, 2013.

  1. Bryan Harvey

    Bryan Harvey Member

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    250-300 yards out C8 started drifting away and not responding to control inputs.
    I initiated a return-to-home. C8 responded and returned directly to takeoff position at altitude, but I was unable to cancel the failsafe or re-establish any radio control whatsoever.
    C8 started counter-clockwise toilet bowl on descent and started drifting away from takeoff position. Just watched in horror as it kept coming down, toilet bowling, and eventually slammed into the side of a trailer with speed.
    Three broken booms, 3 motors, 8 props. Coulda been worse. Luckily no damage to gimbal or camera.

    I would deduce a combo of factors leading to this crash. Firstly, clearly a range issue with my Graupner system, and secondly a GPS issue with the WKM (attributed to the toilet-bowling as it seems GPS was seeking but not finding exact position). Then the failsafe lockout issue (WKM?) combined with pilot error - panic. There are some things I should have tried to reestablish radio control, like switching between flight modes, but I was expecting a nice autoland as I had experienced during tests, and when it started toilet-bowling there was not much time to react.

    I have been flying this machine without issue for two months. On initial flights I tested the failsafe return-to-home and it worked perfectly all the way to landing.

    What's new:
    New location...kind of. I normally live and fly in North Carolina. This crash occurred in Utah. However I have had over 20 successful flights here in Utah prior to this crash. I did not recalibrate my compass/GPS upon arrival in Utah, so this could be a factor.

    I checked internet for solar flares on that day and there was one - but not particularly significant.

    The relatively short range that started the chain of events is most puzzling. It was about as far as I typically feel comfortable flying so I have not pushed beyond that, but obviously should be well below the range limits. I am pulling the Graupner data this morning to see what it shows.

    I think the toilet bowling was my fault as I did not do the recalibration for magnetic deviations in Utah. This was a procedure I just honestly did not think about when I came out to Utah.

    Question: What is the recommended failsafe setting within a Graupner MX (or MC) 20 in combo with the WKM failsafe?
     
  2. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Hi Bryan:
    Sorry to hear of your incident. Does the WKM record the equivalent of the MK's GPX log file?

    As to the MX-20 failsafe, I may have this wrong, but I think the failsafe just puts it into "deer in headlights" mode -- that is, it just locks the controls at particular settings, so I'm not sure what I would want those to be other than 65% - 80% throttle, all other sticks at their neutral position -- the hope being that it would execute a vertical descent.

    Andy.
     
  3. Ben Hall

    Ben Hall New Member

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    sorry about your crash . if you had traveled away from the point that the compass was last calibrated i would certainly have re calibrated in the new flight location . when you said you tried to cancel the RTH how did you try to do that ?
     
  4. Brandon Loeser

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    Sorry to hear about your .... um... c-word. I too have gone into Return to Home on purpose and on accident. To Cancel it.. just switch your flight mode from GPS to ATTI or MANUAL. That should do it. Also there's an update to the WKM software and firmware. Limiting Height and Distance. Haven't tested those features yet though.
     
  5. Bryan Harvey

    Bryan Harvey Member

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    Something weird going on with my Graupner. Rebuilt my machine and all ground range tests were good. Tried a hover at three feet and all was fine for about 2-2.5 minutes then suddenly simultaneous Rx voice warning and power cut to all motors and my C8 dropped instantly to the ground. No real damage, but a real mystery to me.

    Yes, back on crash day I should have tried switching flight modes, hence the mention of "panic" above. I kept toggling the RTH switch, (which during testing had cancelled it.) There wasn't much time to think/troubleshoot. It was not until the last few seconds that I could see it was not going to autoland as it had done perfectly in testing. An expensive lesson for sure, but I sure learned it.
     
  6. Bryan Harvey

    Bryan Harvey Member

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    I think I found my problem, (or A problem) - a bad XT60 connector. During extended motor balancing and testing yesterday I experienced another power out for a fraction of a second. I run dual packs and have a splitter cable running to a single connector that powers my machine. I rarely have a reason to touch the single connector, as always just plugging in the dual packs. Anyway, I started prodding, touching, moving, wires which revealed a short circuit at the bad connecting point. I pulled the connector and sure enough it looked bad - pitted or oxidized especially on the black wire side.
     
  7. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Bryan:

    Could it have been electrical arcing? Don't know whether you still have the connector with wire attached by it would interesting to see an image, if you have the time.

    Andy.
     
  8. Bryan Harvey

    Bryan Harvey Member

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    Andy, I already attempted to scrape off most of the oxidation, so the evidence is gone. The connection is still unreliable so I'm going to replace the Xt60. What would the product of arcing look like?
     
  9. Andy Johnson-Laird

    Andy Johnson-Laird Administrator
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    Arcing would produce intense heat, so the pitting you described would be one possible indication, along with any other signs of melting. The bigger question is why was it arcing (if it indeed was)? Cold solder joint?

    Andy.
     
  10. Thijm

    Thijm Member

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    Just exchanged the Ec5 for Xt90 and arcing is tremendous. Had to use an resistor cable to power up the copter.
    Btw. last week some Co-flyers also experienced an fly away. But with Epic and prime lens. To be never found!

    Very sad if this happens!
    Thijm
     
  11. Bryan Harvey

    Bryan Harvey Member

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    There was indeed evidence of melting at the base of the XT60. The guy who did the soldering is a 20 year RC guy with lots of experience soldering, but I suppose it could still be a cold solder joint. Could there be any other possibilities to consider? What about just old age of that main connection point where all the high powered juice flows?
     
  12. Bryan Harvey

    Bryan Harvey Member

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    Thijm, are you saying the XT connectors are prone to arcing? Why would that be the case? I chose them because they form a very solid connection and when disconnected you don't have to worry about accidentally touching terminals together in transit.
     
  13. Thijm

    Thijm Member

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    indeed they are well made and solid. The reason for using them. But with high capacitor esc they can really spark.
    The ec5 are in case of arcing better connectors.

    Thijm
     

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