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PSA / Warning: This Can Happen To You
3643 25 2015-4-12
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ianwood
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I didn't think they were real. I thought they only happened to people who didn't pay attention to the details. They weren't really flyaways. Well, not any more.



Today, I had a flyaway. It was a perfectly normal flight for 11 minutes. I was reshooting a location I had shot two weeks ago. I had the P2 in a static hover about 10m off the ground (15m from me) while I figured out my last few shots.

It then took off at ~25 degrees down angle at full speed and smashed into the street. Both gimbal and Lightbridge ripped clear off and tumbled across the street. It was over in two seconds. The battery had half-way dislodged and was still on (1 solid, 1 blinking). All four props were destroyed, two right at the hub.

Infographic

Infographic


I gathered all the pieces, cursing profusely and took them home. I then checked everything out in detail.

• The battery is fine. 22 cycles. Balanced. Test flight on my backup P2 was 14.5 minutes.
• IMU, no calibration needed as per the Phantom Assistant. Had advanced calibrated 2 weeks ago.
• Compass MOD is 1403.
• I had checked the props prior to flight and they were fine. Not so much now.
• I ran stress tests on the ESCs / motors. Totally fine. No unusual noise. Balanced bell housings.
• RC calibration is perfect.
• I went back to the site, looked for any magnetic, EMI, RF sources. Nothing.

So that leaves really one maybe two possibilities:

• Lightbridge commanded the movement (no idea if that's even possible).
• More likely, the IMU and / or Naza locked up or received bad IMU data.

With bad data or a frozen IMU, the Naza would get bad reference data for where gravity is and then would command the motors to correct for it. That would create an unrecoverable situation.

Either way... It was a flyaway. They're real. And they can happen to you. Fortunately, it happened in an area where it was recoverable. Gimbal is bent beyond repair. The GoPro somehow took the brunt of the impact. It's gone as are the last 20 seconds of the video so no crash.

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oakspi
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I think that is a pretty good guess about what failed.  I have a friend that had that happen with a 3DR Iris Plus and confirmed by the factory.
2015-4-12
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johnwarr
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Couple of things that spring to my mind,
1st, you must live in the only city in the world with no Wi-Fi, magnetic interference or radio broadcasts.
2nd, in the video of the phantom held down you can see the rapid green LED's indicating a transmitter input. Presumably this was to give the effect of it flying away ?

I am not saying flyway's don't happen, but if you follow DJI flight recommendations the risk will be greatly reduced.


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oakspi
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Why does the video fail 20 seconds before a crash?
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i_anderson
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oakspi Posted at 2015-4-13 01:36
Why does the video fail 20 seconds before a crash?

I mentioned that this seems to be something of a common theme in a similar thread a while back.

As someone noted, it almost suggests a complete, if only momentary, shutdown prior to the thing going crazy.

Is it all units with GoPros? (I could be wrong, but seems these latest tales of woe were all GP (?)

Certainly "concerning" no matter what.

Seems even "due diligence" can't prevent it sometimes.

At least nobody/thing was hurt. (Apart from your wallet of course )
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paul
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Sometimes when I drive near tall buildings, I've had my dashboard Garmin suddenly think I'm 300-500 feet away from where I really am, and then 30 seconds later it will correct itself.  Anyone seen that before?  I assume it has to do with satellite signals either bouncing or being blocked by buildings.  

So I wonder if something similar happened here.  That is, it suddenly thought it was somewhere it wasn't, and tried to abruptly correct?

I know DJI has improved the GPS antenna in the P3.  I hope this makes a difference.
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CapitAn
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Thanks for sharing your experience.
As a new and still overly-cautious owner, l try to keep it in the forefront of my mind what l'm going to do at the first sign of trouble. You say you had 2 seconds. Did you try ATTI in that time, did you throttle up? Did you see any response from the copter at all or are they unresponsive while in a dive or a fly-away?
Thanks in advance.
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ianwood
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johnwarr@live.c Posted at 2015-4-13 01:35
Couple of things that spring to my mind,
1st, you must live in the only city in the world with no Wi ...

It's a common misconception that RF interference and poor GPS cause flyaways. They don't.
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ianwood
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oakspi Posted at 2015-4-13 01:36
Why does the video fail 20 seconds before a crash?

The GoPro was destroyed in the crash leaving the video file incomplete. The only way to recover the file is put it in another GoPro, let it repair the file which cuts off the incomplete last x seconds from the end of the video.
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i_anderson
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ianwood Posted at 2015-4-13 02:57
The GoPro was destroyed in the crash leaving the video file incomplete. The only way to recover the ...

Is that what you did? It seemed that you were saying you had a good, complete, video file that ended ~20seconds before the crash? If I'm correct, why did that one get completed? [Unless it was dumb luck that you stopped recording at that point of course?]
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HermosaDrones
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so now it won't lift the books?
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oakspi
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CapitAn Posted at 2015-4-13 02:47
Thanks for sharing your experience.
As a new and still overly-cautious owner, l try to keep it in th ...

I don't think 2 seconds is enough time to process what is happening, flip the correct switch and have the phantom correct the bad behavior.
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ianwood
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HermosaDrones Posted at 2015-4-13 06:09
so now it won't lift the books?

Yes, it won't lift books. But it did pass the ESC / motor stress test which is what you see in the video.
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ianwood
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oakspi Posted at 2015-4-13 06:17
I don't think 2 seconds is enough time to process what is happening, flip the correct switch and h ...

Exact timing is hard to estimate. I have manual mode set up a flip away and it happened so fast, it had slammed into the pavement before I even got my finger on the mode switch.
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Raybro
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Yes, common thread is video locks up prior to the dive of death. I doubt the phantom would respond to any input from the controller at that point. IMU, FCS , video Tx are locked up.
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oakspi
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Raybro Posted at 2015-4-13 06:51
Yes, common thread is video locks up prior to the dive of death. I doubt the phantom would respond t ...

I don't know much about the GoPro.  Does the camera lag 20 seconds to record the data to the card?  It does not seem probable that it would. It may need some time to end/finalize the recording process as has been suggested.
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Raybro
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I don't think it does. After landing mine, I usually turn off the Phantom first (which frees up the gimbal) then tap on the shutter button on the GoPro to stop recording. It beeps a couple of times and the led indicator turns off after a couple of seconds. Then I power down the camera.  
I have seen in other threads when folks have lost control of the bird, they lose video transmission several seconds prior to the bird going down or flying off.
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birdfolk5555
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It happened to me around flight 30.
It was flying normally approx 60 feet high. Then it stopped responding to the controls. It hovered for a few seconds... began to wobble violently.... then began a steep descent until crashing in the sand.
Hasn't happened since.
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droneflyers.com
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200 flights in urban area?
With that machine?

Lots of possibilities - almost too many since it's a GoPro quad and therefore we don't have stuff like knowing where the home point was actually set (with the DJI app and a goog map).

Poor GPS can definitely cause erratic behavior and so-called flyaways/crashes (I don't like the term flyaway), but if a bird is in GPS mode and things get screwy (telemetry, battery levels, etc.), it can attempt a RTH to a place far far away or above or below where it is.
1.5 bars on the battery - I'm landed by that point, but to each their own. It depends on the version(s) of the quad and apps and settings, etc.

If only one thing or two things caused crashes we'd be able to figure them out and we'd be golden. But I suspect it is often a combination of things - bad contact connections, bad telemetry, etc.....and maybe some bugs that don't show up until other certain things go bad.
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ianwood
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Poor GPS doesn't cause flyaways. It causes ATTI. Even GPS drift / multipath / low horizon SVs won't do it. Especially not with DGPS available. The so called RTH flyaway may exist, but I haven't seen one video that corroborates it. I've seen a ton of misinformation about it. Anyway, this wasn't RTH or poor GPS. I had 10-11 sats and DGPS the whole time. And the lights weren't flashing FS yellow when it happened. They were green.
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Yug
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From word go I have believed the Phantom has the capability of losing control. There have been many theories from members on this forum on whether it's pilot error or machine error.

I believe there is a flaw in the firmware that rears it's ugly head from time to time resulting in a crash or flyaway which is not human error. Only a true BlackBox connected to a Phantom that malfunctions will find the answer to this.

I still hold the belief that one can be as careful as humanly possible but that does not make one immune from the Phantom losing control.

One thing I have learned is if I do have the misfortune of losing control of the Phantom I will not post it on the forum. If I did do something stupid that caused it I wouldn't need to be told that but equally if it happened despite doing everything right I would not be able to stand the comments from the ones who it has not happened to yet who believe the fault lies with the pilot.

Yug
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ronnydsosa
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Flay away ?? More like a crash to me... Your phantom did not fly away to never be recovered.....
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ianwood
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"flyaway" is a catch-all for uncontrolled flight which is what happened. Cost me $1,200 in parts so far. DJI has offered to cover exact $0 so far.
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ianwood
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Yug Posted at 2015-4-13 19:39
From word go I have believed the Phantom has the capability of losing control. There have been many  ...

I actually have a "black box" style logger on my other P2. I was about to put one on this one as well. It logs all the raw sensor data as well as the computed data from the flight controller. If it happens again, I'll have the data!
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Yug
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ianwood Posted at 2015-4-14 12:07
I actually have a "black box" style logger on my other P2. I was about to put one on this one as w ...

Do you have the link for the logger for me to look at it?

Yug
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ianwood
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It's a DIY job so not for the lighthearted but you get all the raw data: http://www.rcgroups.com/forums/showthread.php?t=2071772

There's also Flytrex which has the advantage of a 3G data connection but I don't think they log all the raw data that you get off the CAN bus.
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