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How to Quickly Improve Drone Performance and Extend Flight Time Using a SiP Drone Controller

By Bill Giovino

Contributed By Digi-Key's North American Editors

As more battery-powered drones take to the skies, there is competitive pressure on drone manufacturers to expand the functionality and performance of their designs, while at the same time minimize power consumption to extend flight time. To meet market demand, designers are adding more precise and accurate accelerometers and gyroscopes and upgrading the associated firmware to take advantage of the improved sensors. The physical capabilities of drones are also expanding to include carrying packages and equipment, requiring improved stability and air braking routines to deal with the increased weight.

The problem for designers is that the added weight of the drone, along with the added computational requirements, increases power consumption, which in turn reduces the flight time possible for a given battery size. The additional features, capabilities, and associated electronics also add to development time and the cost of test.

The solution is found in higher integration. This article will introduce a system-in-package (SiP) solution from Octavo Systems that is basically a tiny drone computer. The article will show how the features of this self-contained solution can be used to save significant space and reduce weight to extend flight time, while also lowering the bill of materials (BOM), inventory, development time, and test costs.

Drone technology

Applications for drones are constantly expanding, from small consumer-oriented drones with cameras for family photos or friendly competitions, all the way to more challenging roles such as delivering packages for couriers, keeping track of livestock for ranchers, monitoring crops for farmers, monitoring changing coastlines for environmentalists, and search & rescue operations for first responders. Regardless of application, battery life—as it relates to the flight time—is one of the most critical factors in drone selection.

Battery life is obviously related to the weight of the drone, so for this reason drones use the lightest materials possible that can maintain the aircraft’s framework while under the stress and strain of powered flight. This focus on light weight extends all the way from structural integrity to the electronics controlling the drone.

For proper flight dynamics, the drone must be properly balanced by evenly distributing the weight of the frame and on-board electronic components. The smaller the electronics, the easier it is to balance the weight of the drone. Ideally the center of gravity is at the physical center of the aircraft. Any weight imbalance, no matter how small, must be compensated for by adjusting the propeller rates, and these adjustments over time consume additional power and rob the user of valuable flight time.

Consumer and most commercial drones use Wi-Fi technology for control and data transfer. The further a drone can fly, the more power the Wi-Fi radio must output to keep the drone in contact with its controller, which is another power draw on the battery.

Drone sensors and processing

While drone manufacturers seek to reduce the weight and cost of their systems, users are eager for more functionality and higher performance, making the drone and its firmware more complex. This increases the amount and weight of on-board electronics, while also affecting the drone’s balance.

For example, drones typically use a variety of microelectromechanical systems (MEMS) and other sensors to maintain stable flight while monitoring course and speed (Figure 1). A global positioning system (GPS) module is used to determine aircraft location and direction; gyroscopes are used for measuring pitch and yaw; accelerometers measure drone acceleration and shock forces; barometers are used to measure air pressure to help determine optimal propeller rotation speed for present atmospheric conditions—lower air pressure requires faster rotor speed while high air pressure requires slower speed; and camera and proximity sensors enable obstacle detection and avoidance. Also, multiple redundant sensors may be used for safety reasons.

Image of modern four-prop drone has a wide variety of MEMS sensorsFigure 1: A modern four-prop drone has a wide variety of MEMS sensors, at least one camera, an external memory card for microcontroller firmware or storing photos, and motor drivers for the propellers. (Image source: Octavo Systems)

The outputs of each of these sensors are fed to the microcontrollers operating the drone. The microcontrollers must process all of these sensor inputs and use them to determine the most efficient way of powering the power-hungry brushless DC (BLDC) motors that drive the propellers. However, as sensor technology improves every year, drone manufacturers are putting the latest, most accurate and highest-precision sensors on their newest drones. This requires more complex firmware in order to take advantage of the enhanced capabilities of these sensors. In addition, flight control firmware is always improving, especially for autonomous drones. All of these improvements not only expand the amount of firmware, they also require increased processing power and significantly more memory to process the data accurately.

The expanding electronics and functionality challenge engineers to come up with a lower power, small size solution that can meet the increased demand, while keeping development and test costs to a minimum.

SiP drone devices

The solution to the increased functionality is a higher level of electronics integration. To this end, Octavo Systems developed the OSD32MP15x family of drone-oriented, self-contained computer systems in a single package. For example, the OSD32MP157C-512M-BAA is a powerful device that contains a combination of over 100 discrete and individual die components in a single 18 millimeter (mm) x 18 mm ball grid array (BGA) package (Figure 2).

Image of Octavo Systems OSD32MP157C-512M-BAA complete drone systemFigure 2: The Octavo Systems OSD32MP157C-512M-BAA is a complete drone system in a single package, with a combination of over 100 discrete and die components in an 18 mm x 18 mm package. (Image source: Octavo Systems)

The OSD32MP157C-512M-BAA has two Arm® Cortex®-A7 cores running at 800 megahertz (MHz) (Figure 3). This is enough processing power for very-high-performance drones and allows for seamless processing of sensor data while simultaneously sending precise and constantly changing pulse width modulation (PWM) signals to the four drivers powering the BLDC propeller motors. Each Cortex-A7 core has 33 kilobytes (Kbytes) of L1 instruction cache and 32 Kbytes of L2 data cache. The cores share 256 Kbytes of L2 cache. Flight control firmware can be recursive, and this amount of cache significantly speeds up navigation and sensor fusion processing.

An additional third processor, a 209 MHz Arm Cortex-M4 with a floating point unit (FPU), is also in-package and can be used for auxiliary processing such as managing the camera, battery monitoring, and controlling Wi-Fi communications. Three eMMC/SD card interfaces are available for connecting to external flash cards such as microSD memory. This is useful for loading firmware into the SiP as well as storing camera photos and videos, flight data recording, event logs, and MEMS sensor logs.

Additional memory for the processor cores includes 256 Kbytes of system RAM and 384 Kbytes microcontroller RAM. There are also 4 Kbytes of battery-backed-up RAM and 3 Kbytes of one-time programmable (OTP) memory available for device customization such as a drone serial number or option packages.

Graphic of Octavo Systems OSD32MP157C-512M highly integrated computerFigure 3: The Octavo Systems OSD32MP157C-512M is a highly integrated computer in a single device, appropriate for high-performance drone systems. (Image source: Octavo Systems)

External flash program memory interfaces include two QSPI interfaces, and a 16-bit external NAND flash interface with support for 8-bit error correction code (ECC). This allows for easy access to external flash memory while guarding against memory corruption or tampering.

Two USB 2.0 High Speed interfaces can be used for device configuration and debugging, and also for external USB flash memory if additional data storage is needed.

512 megabytes (Mbytes) of high-speed DDR3L DRAM is used as program memory for the on-board Cortex cores. The DRAM can be loaded on boot from any of the external flash memory interfaces. This provides enough program memory for high-performance flight data firmware. Program memory can be run out of any of the external memory interfaces, but firmware always will execute significantly faster running out of the DRAM.

4 Kbytes of EEPROM can be used to store sensor calibration data, flight control constants, and flight log data. A memory protection feature prevents inadvertent writes to protected EEPROM.

Several security features insure the safety of the system. An Arm TrustZone module along with support for AES-256 and SHA-256 encryption can be used to insure firmware integrity during updates as well as encrypting data in the external flash card. The OSD32MP157C-512M supports secure boot for firmware security and a secure real-time clock (RTC) to prevent tampering with the drone’s timebase.

A wide variety of serial ports include six SPI, six I2C, four UART, and four USART interfaces that can connect to MEMS sensors and GPS modules. Two independent 22-channel, 16-bit analog-to-digital converters (ADCs) allow interfacing to analog sensors such as thermistors and wind speed sensors, which can also perform current sensing and closed-loop motor control. Three I2S interfaces allow interfacing to audio devices such as speakers or buzzers. A camera interface allows a simple connection to most RGB camera modules.

The OSD32MP157C-512M also integrates all the discrete components necessary for the system including resistors, capacitors, inductors, and ferrite beads. This allows a minimum of external discrete components to be used in building a drone system.

For PWM motor control the OSD32MP157C-512M includes two 16-bit advanced motor control timers, fifteen 16-bit timers, and two 32-bit timers. This provides enough PWM signals to control BLDC propeller motors with a high degree of accuracy, as well as any actuators such as camera positioning motors or robotic arms.

Powering the OSD32MP15x

The OSD32MP157C-512M requires only a single 2.8 volt to 5.5 volt power supply, making it appropriate for standard 3.7 volt lithium-ion batteries. An internal power management chip provides the necessary voltages for all the separate internal components. With both Cortex-A7 cores and the Cortex-M4 running at maximum clock speed and all peripherals operating, the OSD32MP157C-512M will draw a maximum of 2 amperes (A). Because of the high level of integration and many operating options, a typical current draw scenario cannot be estimated, leaving it up to the developer to determine what the current draw will be for a particular application.

The OSD32MP157C-512M has a lower current draw compared to the same functionality implemented using discrete components on a circuit board. This is largely due to the fact that using a single die in a closely-packed SiP instead of packaged components dramatically reduces leakage current, and also reduces power lost to pc board trace resistance.

The electrostatic discharge (ESD) rating of the OSD32MP15x family is ±1000 volts human body model (HBM) and ±500 volts charged device model (CDM). For this reason, the device must be handled with extreme care. It is strongly recommended that fingers should never touch the ball grid contact points and that the device only be handled by the edges, and only when necessary. The OSD32MP15x family of SiP devices is also sensitive to moisture. It is recommended that the drone electronics be sealed, which is also a good idea for drone electronics in general as they may come in contact with high humidity, water vapor, clouds, or rain.

For higher performance drones Octavo Systems offers the OSD3358-1G-ISM SiP device. This offers similar functionality as the OSD32MP157 but has a more powerful dual 1 gigahertz (GHz) Cortex-A8 with a gigabyte (Gbyte) of DRAM in a 21 mm x 21 mm BGA package. Because of the high performance of the two Cortex-A8 cores, it does not include the additional Cortex-M4 processor.

Octavo SiP development

For code development Octavo provides the OSD32MP1-BRK flexible prototyping platform board (Figure 4). The board contains an OSD32MP157C-512M SiP and expansion headers for connecting to 106 of the digital I/O and external peripheral signals.

Image of Octavo OSD32MP1-BRK prototyping platformFigure 4: The Octavo OSD32MP1-BRK is a flexible prototyping platform for the OSD32MP15x family of SiP drone devices. It has a slot for a microSD card and a micro USB port for development and debugging. (Image source: Octavo Systems)

A microSD card slot allows the development board to load external flash program memory into the DRAM in the OSD32MP517-512M. A micro USB port is used for development and firmware debugging and also provides power to the board. Boot mode switches determine if the device will boot from the microSD card or any of the external memory interfaces available at the expansion headers.

Conclusion

As drone manufacturers continue to improve their systems’ capabilities, developers are increasingly challenged to provide these capabilities while minimizing power consumption and cost in order to provide the best end-user experience.

As shown, single device, high-performance SiP drone computers provide a very high level of integration. This simplifies the design process while making the drone lighter and easier to balance, thereby lowering current draw and extending flight time, a highly valued end-user requirement.

Disclaimer: The opinions, beliefs, and viewpoints expressed by the various authors and/or forum participants on this website do not necessarily reflect the opinions, beliefs, and viewpoints of Digi-Key Electronics or official policies of Digi-Key Electronics.

About this author

Bill Giovino

Bill Giovino is an Electronics Engineer with a BSEE from Syracuse University, and is one of the few people to successfully jump from design engineer, to field applications engineer, to technology marketing.

For over 25 years Bill has enjoyed promoting new technologies in front of technical and non-technical audiences alike for many companies including STMicroelectronics, Intel, and Maxim Integrated. While at STMicroelectronics, Bill helped spearhead the company’s early successes in the microcontroller industry. At Infineon Bill orchestrated the company’s first microcontroller design wins in U.S. automotive. As a marketing consultant for his company CPU Technologies, Bill has helped many companies turn underperforming products into success stories.

Bill was an early adopter of the Internet of Things, including putting the first full TCP/IP stack on a microcontroller. Bill is devoted to the message of “Sales Through Education” and the increasing importance of clear, well written communications in promoting products online. He is moderator of the popular LinkedIn Semiconductor Sales & Marketing Group and speaks B2E fluently.

About this publisher

Digi-Key's North American Editors