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P3P suddenly fell from the sky

Discussion in 'General Discussion' started by Buddy Moran, Apr 20, 2017 at 9:48 PM.

  1. Buddy Moran

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    Has this ever happened to you? Is there any reason DJI wouldn't honor the warranty?* The AC was flying smoothly using the AutoPilot Waypoint mode of a 9 hole mission. The AC suddenly fell from the sky at the halfway point of the mission with 60% of battery life left, at about the 11th minute, from an elevation of about 40 meters during the peace of dawn. I can see no apparent cause of the crash. Attached are (1) a screen capture of the completed flight route when the crash happened, and (2) a compressed zip file with the log data of the flight. This YouTube video shows the flight up to the crash:
    Please forgive the soft and grainy quality of the video. It is from my iPhone which videoed computer screen running the recovered video. The video file was truncated because the recording wasn't properly turned off as a result of the crash. The recovered, but unstable, h265 file format video can only be viewed with VLC. There doesn't seem to be any other way to convert it. Most of the (iPhone-recorded) video is sped up 2x. The video speed is then back to normal just before the crash, which actually happens at about 10:44 (mm:ss) of the raw video. In this sped up version it happens at about 5:28. (I'm still trying to fully recover the video. The lighting was perfect for post processing.)
    Music: Clouds by audionautix.com
    *DJI Thailand says it needs to be sent to Hong Kong to analyze. It could take 2 months before any decision on what my options are.
     

    Attached Files:

  2. msinger

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    Were all of the props attached when you found your Phantom?
     
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  3. jwmcgrath

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    Bird strike? That last second of video sure looked like something sudden and catastrophic, and hard enough to immediately jam the camera out of position...
     
  4. Buddy Moran

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    No. Unfortunately, it had fallen into a creek. When retrieved, one prop was missing. I can swear I tightened them properly. I have also been reviewing the video several times for any clue of instability that might result from a loose prop. I couldn't find any. If the crash was a result of the prop flying off, what could have caused that to happen?
     
  5. Buddy Moran

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    JWM, these are three frames when the AC starts descending. I can't see any hint of something coming into contact with the it.
     

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  6. sar104

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    Unfortunately, if the entire prop, including the hub, was missing then that is most likely the cause of the failure. The sudden rotating fall is exactly what losing one motor will produce. The front arm that drops first (front right, as seen in the video) would be the motor that I would expect to be missing its prop.
     
  7. JWhitaker

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    Bird Attack.. Or it got smacked by something. X-Files.
     
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  8. Buddy Moran

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    That sounds likely, SAR104. But what would cause that to suddenly happen after flying smoothly for about 11 minutes? Would't you expect to see some destabilization in the video just before a prop flies off?
     
  9. sar104

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    I would not expect to see much in the way of precursor destabilization because the prop is either on the motor, via self-tightening under load, or it is off, pretty quickly, on motor deceleration. There is no point at which it is going to be on, but wobbly, for more than a few rotations.

    I've never lost a prop, but having watched videos of such events, they look very similar to yours.

    Was the front right (from camera view) the missing prop?
     
  10. Buddy Moran

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    sar104, Yes, it was the front right. I've also studied at videos of props flying off the past couple of days. I notice those that just drop down, like mine did, didn't stay up for more than a minute. Those that managed to stay up longer would start to wobble or spin around, and then spin while falling. I didn't see any video showing a P2 or P3 where the props stayed on for up to 5 minutes.
     
  11. sar104

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    OK - well I think that is very strong evidence that it was front right prop loss, although why it stayed on for as long as it did is certainly a good question.
     
  12. jwmcgrath

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    I certainly think prop loss needs to be considered suspect, but there are two factors that lead me to think bird strike;

    1- the sudden nature of the destabilization. It was quick and violent and there was no warning

    But even more so;

    2- the immediate repositioning of the camera on such an extreme angle.

    While I can understand a prop loss, and the one that's missing being the one that was suspect, I can't see that having caused the camera to go so suddenly askew.

    You wouldn't see the bird strike if it happened from behind or the side, out of camera range.
     
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  13. sar104

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    Can't be ruled out, but if you look at the video frame by frame it appears that the gimbal is simply trying to keep the camera pointed in the forward direction while the front right of the aircraft suddenly drops. Are you suggesting that a bird knocked the prop off? If not, the aircraft would have recovered, presumably, rather than crashing with a prop missing.

    I also can't imagine how a bird could be so situationally unaware that it would collide with a noisy, slow-moving Phantom, but that's a different issue.
     
  14. jwmcgrath

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    In a scenario involving the aircraft striking something like a bird, then yes I'd say that the strike itself caused the prop loss because of course you're right, the aircraft likely would have otherwise recovered.

    I agree about the bird's situational awareness, but strangely enough it does seem to happen!

    I'll try watching the video on a proper device, everything I've seen has been by phone so far. I didn't think the camera could view so much of the arm without an external force applied to it but I could be wrong on that.
     
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  15. syotr

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    I don't think a bird strike would make a prop spin off. It might shatter a prop leaving the hub intact. Any impact with a spinning prop would tighten it, not loosen it. An ESC failure can make a prop spin off even if it was on pretty tight. A motor wire could have come loose from a bad solder joint. This will throw a prop as well.
     
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  16. Multicoptertec

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    Since a prop is missing, you can be 99% sure that's what caused the crash. How tight do you normally tighten your props? Were they left in place in a case? Did you find the missing prop, and how far was it from the crash site? Any bird blood or feathers on the plastic? Lastly, what is the extent of the damage to the P3P? Unless you have the DJI protection plan, they most likely won't repair this under warranty.
     
  17. macoman

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    I am suspecting that the prop were installed incorrectly, in the wrong colors?
     
  18. sar104

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    I've seen reports of large birds attacking UAVs, but have there been confirmed cases of accidental collisions?
     
  19. sar104

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    No - if that happened, which would be difficult since they are oppositely threaded, it would not be able to take off and fly.
     
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  20. syotr

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    I did a test some time back to see if suddenly slowing a motor (active braking) could make a prop fly off. I installed a prop as loose as possible and manually grabbed the motor bell at different speeds. I found that it was nearly impossible to make this happen. Just starting the motors would snug up a loose prop pretty well. Only at the very highest speeds, with a completely loose prop was I able to make one fly off. I also tested the effect of losing one motor phase as would happen with a disconnected wire or ESC glitch. In this case the prop would fly off instantly and consistently even if it had been installed pretty snug. I think this is more likely the cause of many of the prop loss crashes that were blamed on props not being installed tight enough.
    At times in this video, the prop looks like it is moving slowly but it is just turning at a rate near the camera's frame rate. At the end of the video, you can see what happens if you disconnect a wire and lose one motor phase. Obviously, this was not a P3 but the physics should be the same.
     
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