A very interesting post over at the Phantom Pilot forum.
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: http://www.ianwood.com/docs/anatomy-of-a-dji-flyaway-v1.pdf