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Phantom fell from the sky

Discussion in 'General Discussion' started by TickTock, Apr 10, 2013.

  1. TickTock

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    Had an odd experience yesterday. Was goofing off in atti mode at a fairly high altitude aggressively diving (as much as it will let you) and swooping back up. After a high speed dive/climb combo, I lost control of the Phantom. It was still under power, but it dropped. It was as if I had the throttle all the way down. It stayed level and and just dropped. Nothing I could do with the transmitter could change it's behavior. Would have hit the ground hard if not for the good fortune of it hitting a cottonwood tree first and getting hung up in the leaves. When I climbed the tree to get it, it looked off. No LED. But as I fished it out of the tree it came back on and started the GPS lock & sensor warmup sequence. Battery was still solidly connected. No GoPro attached so no chance the Wifi came on and interfered. Phantom still seems to work fine (leaves&branches buffered the fall nicely) but I have lost a bit of confidence in my flying not knowing what happened since I got lucky that time. Any ideas what could cause it to fall like that?
     
  2. Sac D

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    No idea.

    And that's the kind of thing that should make every Phantom pilot a little nervous. It seems like every now and then they just go crazy for no reason.
     
  3. Audaciter

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    Does anyone know if all the Phantoms that develop control issues are still using the DJI radio system, or if it happens
    with any and all controllers.
     
  4. auck

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    could you have over taxed the battery with the power dives and climbs? there has been reports of the LED flashing red with aggressive altitude climbs due to the draw of voltage on the battery to perform such climbs. you said it "was as if I had the throttle all the way down". In the low voltage second stage scenario, "the center point of throttle stick will move up slowly to 90% of endpoint" & "When the center point is at 90% of endpoint, aircraft will still ascend slowly if you continue to pull the throttle stick, and the control of Pitch, Roll and Yaw are the same as before". Basically this means that you pretty much loose all throttle if the throttle stick is below 90% (causing the "as if throttle all the way down" feeling), but you are still able to rotate and turn the craft.
     
  5. BadWolf

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    Vortex Ring State.
    http://en.wikipedia.org/wiki/Vortex_ring_state



    .
     
  6. Sac D

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  7. BadWolf

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  8. TickTock

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    Interesting. I suppose it is possible VRS explains it but I could see the craft well enough to see that it was maintaining attitude (stayed flat and I don't think it was yawing) just not altitude. Sounds like VRS is accompanied by attitude instability. However, maybe the NAZA is quick enough to function well enough to stay flat even under these conditions... It happened pretty fast - I only had about 2 seconds from the time I realized I was no longer in control to it landing in the tree and I spent most of it trying to push the throttle further than it can go :). Maybe I should have tried the right stick sooner.

    One thought I had was could I have gotten inverted? Has anyone done this in manual or other? How does the NAZA behave in this condition?
     
  9. BadWolf

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    The 2 main causes of VRS.

    1. Descending at more than 300 feet per minute.

    2. Hovering in a stationary position at an altitude above 10 feet.

    I also think that prop design can contribute to this phenomenon.
     
  10. jdawson

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    The more then 300 ' per min is a scale issue on a heli. So it could be quite a bit less on a quad.
     
  11. davidharpe

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    I had one of these today - phantom fell out of the sky. After reading up on VRS I'm pretty confident that's what happened:

    [youtube]http://www.youtube.com/watch?v=WaqVfTofzSg[/youtube]

    I'd been hovering for awhile at altitude and was just starting to descend when it happened. Caused the quadrocopter to pitch vertical with a subsequent loss of altitude. Ran out of sky before recovery. Fortunately the ground was soft...no damage to copter or camera. Was up and flying again in a couple of minutes.

    I didn't know anything about VRS until this happened - a friend pointed me to the article once he saw the video. I've only been flying for a couple of weeks and to be honest I'm surprised it hasn't happened before. Up until now I would do some pretty rapid vertical descents and always thought the bumpy ride was just part of it. Didn't realize I was close to losing it completely...until today. :)
     
  12. FangsCPO

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    VRS???????

    Sent from my SCH-I535 using Tapatalk 4
     
  13. davidharpe

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  14. Audaciter

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    Is that condition effecting just one prop, or all 4 ? It seems unlikely for all 4 to experience the same phenomenon.
    also, it looked as if while descending, your quad was traveling forward, and not straight down, so at some point
    had perhaps broken free, but was not able to generate enough power to overcome its downward trajectory.

    Interesting topic for sure. Glad your Phantom was not badly damaged.
     
  15. edunwody

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    Got in one of those in the Ga Mountains filming Lance Armstrong. It ain't fun. He was leading the Tour de Georgia and we blew every leaf off a tree right in his face to recover. He was not a happy man.

    E

    Edit: Not a Quad. A Bell Jet Ranger 206.


    Sent from my iPhone using Tapatalk
     
  16. mikrob

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    I am sure those problems seem like the good old days for Lance now.
     
  17. edunwody

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    Yep, met him a few times before the leaf incident and he was pretty much a real jerk.

    E
     
  18. marcus_canada

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    I have a few worries about the low voltage cutout systems in the ESC's myself. I'm wondering if your ESC's were surging past their capacity and cutting off momentarily, ("LVC mode"), if you were hammering on the lipos.
     
  19. howardmaryon

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    The VRS solution is very interesting, I suppose the air around the props of a tiny (compared to a Chinook) multirotor is subject the same laws of fluid dynamics and aerodynamics. The battery issue is worth considering though. I loaded up my Phantom to the limit with camera, gimbal, accessories, brackets etc, and apart from unusably short battery life, I noticed that when hovering in windy conditions, I could get red battery warnings even a few seconds into a flight, by trying to draw too much current to the motors to stay in one place. It may be possible to trigger the battery fail condition under very high drain conditions, if the drain pulls the current down for long enough, or is that just electrical ignorance on my part? I changed to a more sensible loadout and dont get the problem anymore.