The DJI Spark drone was one of the most anticipated drones ever, and for good reason. An EDN teardown gives a glimpse at how it was done.
Drones are both fun and useful, but from a purely engineering point of view, they are where the rubber hits the road when it comes to the classic trade-offs of power consumption, processing performance, weight, size, and cost. Packing more sensors, actuators, and RF communications per square millimeter than most electronics systems, they literally beg to be torn apart to see how they did it. So, we took the DJI Spark drone and did just that.
This was a “total destruction” teardown, and it may still need a bit of help from you to ID some parts here and there. And if you’re in the mood to experiment with your own design, we’ll also introduce a very inexpensive mini-drone development kit, the STEVAL-DRONE01, that’ll do most anything you need it to do to whet your drone appetite and get you experimenting.
Why the DJI Spark drone?
The original plan was to go inside the UVify OORi, which was designed for racing by a couple of drone racing enthusiasts. By design it is fast—very fast. At $295 it was fairly inexpensive, but it was also very difficult to control for a novice (like myself) and its impossibly short battery life of only two minutes made learning a test of patience. It can go from point A to point B quickly, but only in good hands. Otherwise, expect to hit everything in between, including the ground, multiple times.
There was also the fact that it didn’t quite have enough bells and whistles, such as object detection and avoidance, return to home, voice control, and tracking capability, to make it interesting. Enter the DJI Spark. At ~$450, this had all the key features, and it was made by DJI, the king of drones. This was built for fun, for both experts and novices alike.
The kit torn down for this article was the Fly More Combo, which includes an extra two batteries, propeller guards, extra propellers, a handy bag to carry it around, and of course the drone and controller. As with many designs, the controller has the main control buttons and joysticks, while acting as a cradle for a smartphone that functions as a display as well as running the main DJI drone control app.
Figure 1 Here are three views of the DJI Spark drone from the Fly More Combo kit, including the charging dock, propeller guards, extra propellers, and the controller, shown under the two extra batteries on the far right. Splurge for the extra batteries: they’re worth it.
At the time of its debut, the Spark was one of the most anticipated drones ever, and for good reason. Out of the box it had a “quality” feel about it; small, dense, solid, and elegant. You know you’re holding something well made. It has a range of 2000 meters, weighs 0.66 lb (without battery), and measures 5.6×5.6×2.2 inches. Its 1480 mAh, 11.4V battery gives it a flight time of 15 minutes (hovering) and it has a maximum speed of 31 mph.
Conveniently for experts and out of necessity for novices, the drone has multiple intelligent flight modes. It also has obstacle avoidance in two directions using infrared sensors, and in five directions (total) using the 12 megapixel CMOS camera. The camera outputs video with a resolution of 1920×1080 @ 30 fps and is stabilized using a two-axis gimbal for pitch and roll. A third axis for yaw/rotation stability would have been nice.
The drone operates in both the 2.45- and 5-GHz bands and also includes GPS/GLONASS capability. Its many features can be viewed at the main DJI Spark information landing page. Suffice to say, it was a pleasure to use, and was so well made that it was a shame to tear it apart, but that’s the gig.
Inside the DJI Spark drone
The Spark is well constructed so it took a bit of work to get inside. The process began with exposing its underbelly to remove the screws holding the top cover on (Figures 2 and 3).
Figure 2These views show the top and underbelly of the DJI Spark.
Figure 3 With the top removed, the main cooling system is exposed.
Taking the top off exposed the main cooling system, which uses a horizontal fan to drive air down the heat sink’s channel guides. The thermal management system sits atop an EMI shield, beneath which lies the main electronics. The main GPS module is replaceable for $30 to $50
A view from the rear shows the micro USB interface and memory card slot, as well as two of the four brushless DC (BLDC) motors with their LED lenses underneath (Figure 4). While “pretty,” the LEDs also make the drone highly visible at height during daylight and especially at dusk or in darkness, an important factor for regulatory compliance.
Figure 4 A view from the rear shows the micro USB interface and memory card slot, as well as two of the four motors with their LED lenses underneath.
The next step involved removing the thermal management system and EMI shields to expose the top of the main board (Figure 5).
Figure 5 The main board with EMI shields removed shows thermal paste covering nearly every IC.
Removing the thermal paste gives a clearer view of the massive brainpower driving the Spark (Figure 6). It’s truly packed!
Figure 6 This up-close view of the top of the main board has the thermal paste removed (mostly).
It’s hard to know where to start with the Spark’s processing horsepower, so we’ll start with the motor control section (at left of Figure 6) beginning with STMicroelectronics’ STM32F303 MCU (Figure 7).
Figure 7 The main Spark board comes packed with an STMicroelectronics STM32F303, an Intel Movidius MA2155 VPU, a Leadcore LC1860C SoC, and an Atheros/Qualcomm AR1021X dual-band Wi-Fi SoC.
The STM32F303 is a mixed-signal processor that performs much of the motor control functionality. It is based on an Arm Cortex-M4 microcontroller running at 72 MHz and supported by a floating point unit (FPU) and DSP instructions. Also on board the ‘32F303 are up to seven fast and ultra-fast comparators (25 ns), up to four op amps with programmable gain, up to two DACs, up to four ultra-fast 12-bit ADCs, and motor control timers (Figure 8).
Figure 8 STMicroelectronics’ STM32F303 is based on an Arm Cortex-M4 with FPU and DSP functions but also packs high-speed DACs, ADCs, comparators and optimized memory, among other features, all focused on minimizing latency. (Source: STMicroelectronics)
The emphasis here is on low latency for rapid response times for both accurate control and object avoidance. This is supported by the use of Core Coupled Memory SRAM (aka routine booster). This memory architecture boosts time-critical routines and according to STMicroelectronics, it’s up to 43% faster than flash execution.
The other half of the motor drive sections comprises two Monolithic Power MP6536 three-channel half-bridge driver ICs to drive the four three-phase BLDCs.
Down along the right is an Atmel/Microchip Technology ATSAME70Q21 Arm Cortex-M7-based MCU running at up to 300 MHz and a Leadcore Technology LC1860C quad core Arm-based system-on-chip (SoC) running at 1.45 GHz. The processors are supported by a Micron Technology 71A98 JWB30 low-power DRAM (LPDRAM).
The ATSAME70Q21 features 16 Kbytes of ICache, 6 Kbytes of DCache with error code correction (ECC), single and double-precision hardware FPU, and a 16-zone memory protection unit. The LC1860C is based on a 28 nm process and along with a quad-core Cortex A7, it has a dual-core MaliT628 and can handle 1 Gpixels/s. This is the main image processor.
At the bottom of Figure 7 is the Atheros (Qualcomm) AR1021X dual-band 2.45 GHz and 5.8 GHz Wi-Fi SoC. It is designed for 2×2 MIMO and has its own internal power amplifier (PA) and low-noise amplifier (LNA). Around and up the left side is a Leadcore LC1160 power management IC (PMIC), and above that is an Intel Movidius MA2155 vision processing unit (VPU) with 1 Gbit of DDR memory and secure boot capability.
The use of a Leadcore 1.45 GHz SoC and an Intel Movidius neural network processor says everything about how seriously DJI takes its drone designs. Leadcore is based in China and specializes in SoCs for smartphones—the ultimate platform for functionality/mW/mm3 trade-offs—and Intel bought Movidius for its advanced neural network-based image classification capability that was, and remains, much desired for autonomous vehicles. In the Spark drone, it is used to map the environment.
The rear of the main board holds the passive and discrete components, and shows the USB OG port and SD memory card slot (Figure 9).
Figure 9 The rear of the main board is mostly made up of passive and discrete components, as well as the USB OTG port and memory card slot.
The secondary board holds the GPS/GLONASS components (Figure 10). The heart of the Spark’s navigation system is the u-blox M8030-KT GNSS IC (professional grade version). This chip can do concurrent reception of 3 GNSS signals (GPS and Galileo and either GLONASS or Beidou) and has a sensitivity of −167 dBm.
Figure 10 The navigational heart of the Spark is the u-blox M8030-KT GNSS IC.
Camera gimbal and distance sensors
The camera module hangs under the chassis in a downward-facing angle of ~45°. It uses a two-axis gimbal that pivots using an elastic band connected to the chassis (Figure 11). It’s controlled by a drive mechanism in the arms.
Figure 11 The camera module (top) is attached to the chassis using an elastic band and is controlled by a drive mechanism in the arms.
At the front of the drone are 3D range sensors based on reflected LED signals (Figure 12). In the middle is the main power distribution center (to the motors) and at the bottom are the Wi-Fi antennas.
Figure 12 Removing top PCB exposes the main power distribution layout harness and the Wi-Fi antennas. At the top of the image is the front of the drone, which contains a forward-facing 3D ranging system based on reflected LED light, shown separately on the left.
The sensors have a range of 16 feet and can detect diffuse reflective surfaces with >20% reflectivity that are larger than 20×20 cm, so it can easily detect and avoid walls, people, and trees.
Underneath the chassis, facing downward, are a sonar and IR ranging combination for height detection (Figure 13).
Figure 13 An IR and sonar combination underneath the chassis keeps track of the drone’s distance from the ground.
All told, the DJI Spark drone is a well-made system, but it had its quirks. For example, the QDR codes for the Wi-Fi connection didn’t work, and the firmware update caused the drone to lock. Still, the app worked great using a Pixel 2 Android phone.
Drone development kit for experimentation
For any designer considering a drone-type design, it’s worth checking out the STMicroelectronics STEVAL-DRONE01 development kit. It has the high performance STEVAL-FCU001V1 flight controller unit (FCU), as well as the motors, propellers, plastic frame, and battery needed to assemble a mini-drone.
The flight controller unit runs the firmware (STSW-FCU001) to control the speed of each connected motor and to stabilize the drone. To achieve this, the STM32F4 microcontroller hosted on the board analyses data from the accelerometer and gyroscope sensors to provide highly accurate stability and control. The FCU board includes a Bluetooth Low Energy SPBTLE-RF module, so you can turn your smartphone running a dedicated app into a remote control unit.
Patrick Mannion is an engineer, writer, and editor who has been analyzing the electronics industry for over 25 years. He is owner and founder of ClariTek LLC and President of TechWire International.