Unmanned System Data Protocol and Format: DJI Phantom 4

Introduction

            This research activity will provide an in depth look at the sensors and data methods utilized on DJI’s Phantom 4 unmanned aircraft. The DJI Phantom 4, released in March 2016, is a quadcopter manufactured by Chinese technology company Dà-Jiāng Innovations Science and Technology Co., Ltd (DJI). The Phantom 4 is part of a series of small unmanned aircraft aimed at commercial, amateur, and hobbyist use at a relatively low price point between $499 USD to $1499 USD (DJI, 2017a). Each iteration of the Phantom series brings additional sensors, safety, and software capabilities to an already impressive system. The Phantom 4 includes obstacle detection and avoidance and additional flight modes unlocked by the addition of new vision sensors. Sensors onboard the Phantom 4 will be discussed in depth later in this activity. The Phantom 4 weighs in at 3.04 pounds including the battery and propellers (DJI, 2017b). The aircraft has a diagonal size of 13.8 inches and produces a flight time of 28 minutes (DJI, 2017b), 5 minutes more than its predecessor, the Phantom 3 (DJI, 2017c).

Data Format, Protocols, and Storage Methods

            Flight logs from the Phantom 4 are captured in two filetypes, DAT (data file extension) and TXT (text file) (NVDrones, 2016). The DAT file is stored on the aircraft while the TXT file is stored on the device used as a ground control station (GCS), both are encrypted (NVDrones, 2016). A log file contains a wealth of information gathered by the aircraft during flight, including aircraft GPS location, battery voltage, battery temperature, aircraft speed, motor speeds, motor temperatures, timestamps, camera gimbal angle, and much, much more. Currently there is not a standard protocol for logging flight data on unmanned aircraft, different manufacturers use proprietary protocols with varying levels of transparency. There are some national and international efforts to standardize log files across manufacturers.

            The Phantom 4 stores data in several locations. The flight controller itself stores critical flight data (DJI, 2016). A flight recorder onboard the aircraft records flight telemetry, aircraft status information, and other data (DJI, 2016). The mobile device used to run the DJI GO ground control station app stores the aforementioned DAT and TXT log files. In addition, some data is stored on DJI servers in the cloud when the mobile device is synced using the DJI GO app.

            Images and video captured from the onboard vision camera are stored on a Class 10 or UHS-1 rated Micro SD card onboard the aircraft in FAT32 or exFAT file system formats (DJI, 2017b). Images are captured in JPEG or DMG (RAW) formats while video is captured in MP4 or MOV formats using MPEG-4 AVC or H.264 compression codecs (DJI, 2017b). These formats are industry standard and are supported by most commercial drone manufacturers.

Exteroceptive Sensors

            The Phantom 4 has a suite of exteroceptive sensors to assist in collision avoidance, object detection, accurate positioning, and image capture (still and video). Stereo vision sensors are placed in the front and bottom of the aircraft for collision avoidance and positioning. These sensors can detect obstacles from 2 to 49 feet in front and below the aircraft (DJI, 2017b). The forward field of view is 60 degrees horizontally and plus or minus 27 degrees vertically (DJI, 207b). The downward field of view is 70 degrees to the front and rear, 50 degrees to the left and right (DJI, 2017b). The bottom of the aircraft houses two ultrasonic sensors to measure the distance to the ground. A image camera is attached to the bottom of the aircraft on a 3-axis gimbal. This camera captures still and video images with a 1/2.3” CMOS sensor, effectively capturing 12.4 million pixels with a 94 degree field of view (DJI, 2017b).

            Sensor power specifications for the Phantom 4 are not disclosed by DJI. The onboard LiPo 4S battery is rated at 5350 milliamp hours, 15.2 volts, and 81.3 watt-hours (DJI, 2017b). This one battery is powering the entire aircraft, including the electronic speed controllers, propeller motors, CPU, cooling fan, gimbal, camera, LED position lights, GPS and radio transmitters, and any other onboard systems. As stated previously, this aircraft is capable of 28 minutes of flight.

Alternative Data Treatment Strategy

An alternative data treatment strategy I would recommend for future Phantom series aircraft is additional capabilities in the cloud using cellular data. Large unmanned aircraft used for military reconnaissance missions are controlled using GPS satellites while simultaneously downlinking data. I believe this same approach can be used for commercial and recreational unmanned aircraft using high speed 4G cellular data networks. As unmanned aircraft push the boundaries of beyond visual line of sight operations, a longer range data connection will be necessary to control the aircraft and download data. Advanced video codecs such as H.265 will be necessary to reduce the amount of data sent from the aircraft to the ground control station.

References

DJI (2017a). Phantom 4 Product Page [Webpage]. Retrieved on 12/12/2017 from https://store.dji.com/shop/phantom-series

DJI (2017b). Phantom 4 Specs [Webpage]. Retrieved on 12/12/2017 from https://www.dji.com/phantom-4/info#specs

DJI (2017c). Phantom 3 Professional Specs [Webpage]. Retrieved on 12/12/2017 from https://www.dji.com/phantom-3-pro/info

NVDrones (2016, Jun 6). How to View DJI Flight Logs in 4 Easy Steps [Blog post]. Retrieved from https://blog.nvdrones.com/how-to-view-dji-flight-logs-in-4-easy-steps-2e5c6521c6a7

DJI (2016). Phantom 4 User Manual [Brochure]. Retrieved from https://dl.djicdn.com/downloads/phantom_4/en/Phantom_4_User_Manual_en_v1.0.pdf