Known as a 'FlyAway', erratic autonomous flight has been reported in drones using a Naza flight controller from DJI, most notably the DJI Phantom. During a FlyAway pilots see the drone FlyAway, ignoring their control input. In a few cases, normal control has been regained. With symptoms inconsistent between reported instances, the cause is difficult to pinpoint. Manufacturer DJI has been reluctant to acknowledge the problem.
A survey of FlyAways was started by PhantomPilots.com user 'Spork'. Phantom and Naza users are encouraged to fill out the survey regardless of if they have experienced a FlyAway or not. The survey is available here and survey results are available here.
With 39% of survey responses confirming at least one FlyAway with their Naza flight controller, an official response from DJI seems reasonable to expect. The only good news received from the survey comes from Naza-H owners with no reported FlyAways.
Unfortunately for Phantom owners, DJI's response to the FlyAway problem was to blame users for not properly following the instructions.
Analysis of a FlyAway
Seeing an expensive piece of equipment disregard your commands and take off in a random direction is frustration at an unparalleled level. Because so many of these FlyAways drones are lost never to be seen again, video footage from any FlyAway can be incredibly valuable in diagnosing the problem. Additional On-Screen-Display video overlay information coming from the flight controller, like what the DJI iOSD offers, can be valuable in conveying internal information about the flight controller at the time of the FlyAway.
After reviewing several videos of FlyAways posted on YouTube there seem to be two different types of FlyAways.
The first is where the drone enters an erratic flight pattern similar to the way in which water drains down a toilet, see here and here. This could be caused by incorrect IMU information causing the drone to become unstable and unable to self level.
The second is when the flight controller receives faulty GPS information either on takeoff when the home location is recorded or in-flight causing the drone to think it is too far from its original takeoff point. In either situation the drone flies in a straight line towards its destination, see here and here.
Our Best Guess
With inconclusive evidence as to the cause of FlyAways we can only make a best guess as to what causes this erratic behavior with some Naza flight controllers.
- GPS Glitches - if the flight controller is not programmed to throw out garbage GPS information (an updated location is suddenly more than a mile away), the drone may think it needs to 'return home' causing it to fly away from the user. This doesn't take into account user override input like switching the flight controller out of GPS mode.
- Component Failure - drones are complex systems and electronic manufacturing is difficult; solder joints may crack leading to bad connectivity and components may fail without warning. Check out the 'Bathtub Curve' entry on Wikipedia regarding manufacturing failures.
- Unexpected Failsafe Activation - failsafe settings can be changed through DJI's software. Loss of signal and low battery are the two most common failsafe settings. However, neither is likely to cause a FlyAway unless concurrent with a GPS glitch causing the drone to think it is far away from home.
- Electromagnetic Interference (EMI) - components like the speed controllers and motors can create significant EMI which may interfere with the compass (magnetometer) and possibly the GPS radio. For this reason the magnetometer is positioned on the landing gear, as far from these EMI creating components as possible.