Anatomy of a DJI Flyaway


A very interesting post over at the Phantom Pilot forum.

From ianwood:

I had my first ever bonafide flyaway about 6 weeks ago. I had my theories, bought $1,000 in replacement parts, rebuilt and moved on. Then it happened again.

This time, however, I had a data logger attached to the Phantom, a custom made miniature "black box" that records 75+ different flight parameters 5 times per second. I've spent the past day analyzing the data and I've discovered some things that I didn't suspect before. 
None of the sensors including IMU, compass, GPS, etc. were to blame. The battery, ESCs, motors did exactly as they were supposed to do. There was no loss of connection, GPS interference or any other external factors.

The NAZA locked up. It had intermittent freezes that stopped it from functioning normally. Here is a snapshot of the logged data from when the NAZA stopped working normally.


At 12 minutes, 45 seconds, the data shows 5 anomalies:

  • The Course Over Ground (COG) freezes. It had been fluid all throughout the earlier part of the flight.
  • The speed (Total SPD) changes to 769,361.92 m/s. It had been normal throughout the earlier part of the flight.
  • The satellite count (SAT) jumps to 204 then returns to normal.
  • Erratic updates of ATTI pitch and roll values. 2Hz or slower.
  • Erratic updates of motor speed. 2Hz or slower.

The cause is likely to be one of two things:

  • Defective hardware in NAZA (e.g. cold solder joint) that took several flights of light vibration to manifest.
  • Firmware defect when flying in edge condition (corner of the envelop) that rarely manifests.

I am working on recovering the video (file is corrupted due to loss of power) and I also have a 3D "fly through" of the incident which I will post later.

I've included a more detailed analysis of the data which is in the PDF link here:

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  • That's great. While it's flying away at warp 9.8, it can have a 360 view of itself crashing.

  • Makes you want to toss more money at DJI:


    CPU freezing?  Give more cycles to process...

  • Distributor

    A Borg transwarp coil - When 769,361.92 m/s isn't enough.

  • In other news, DJI releases Phantom IV that includes a Borg transwarp coil.

  • I hope dji read this post and do something.
  • I grounded 3 dji naza eventhought they fly well with no issue. Just use Pixhawk, AUAV X-2 and Naze32, much more confidence when fly with them. Can't wait for Pixhawk 2....
  • Guys,  to be sure:  Ian wood is the author of this work, not me.  I just thought it was worthy of attention in this forum ...

    I fly predominantly  Pixhawk but also have an Octo running DJI Wookong, and a Phantom for fun. No issue  so far with  either of them after hundreds of flights, but that flyaway issue has always worried me ...

    John Arne: +1.

  • A very good job Oliver. I think that this data are very importan for DJI, they should pay you....

  • Developer

    A classic example why open tends to result in more robust software in the long run.

    On APM a bug like this would have instantly resulted in logs from multiple users, and much discussion on the forums with actual data to compare instead of just speculation. On the other hand, when closed software/hardware crashes the user don't get any information, and as a result the developers also don't get the needed information to verify and fix the problem.

  • Since I had my s800 with a WKM flipping I did not have more confidence and do not know what to do because DJI  gives no satisfaction.
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