Reliable systems for micro aerial vehicles -- MAV challenges
Editor's Note: Embedded designers must contend with a host of challenges in creating systems for harsh environments. Harsh environments present unique characteristics not only in terms of temperature extremes but also in areas including availability, security, very limited power budget, and more. In Rugged Embedded Systems, the authors present a series of papers by experts in each of the areas that can present unusually demanding requirements. A separate excerpt of the book addresses fundamental concerns in reliability and system resiliency.
This excerpt describes specific requirements and approaches for addressing reliability in unmanned micro aerial vehicles (MAVs) presented in the following installments:
Elsevier is offering this and other engineering books at a 30% discount. To use this discount, click here and use code ENGIN317 during checkout.
Adapted from Rugged Embedded Systems, Computing in Harsh Environments, by Augusto Vega. Pradip Bose, Alper Buyuktosunoglu.
CHAPTER 7. Reliable electrical systems for micro aerial vehicles and insect-scale robots: Challenges and progress
By X. Zhang, Washington University, St. Louis, MO, United States
The dream to fly has sent men on an ardent pursuit to build ever more sophisticated aerial vehicles. Over the years, steady progress has been made to miniaturize such systems and has led to prolific development and maturation of drones. Recent research advancement endeavors to drive the miniaturization further to the micro scale, and promising prototypes are being developed to explore this exciting yet untrodden frontier. In this chapter, we present the progress our research team has made on building an insect-scale aerial vehicle and zoom into the critical reliability issues associated with this system. Since many such systems are envisioned to operate in harsh environment hostile or harmful to human beings and have stringent design requirements and operation constraints, reliability becomes a first-class design consideration for these microrobotic systems.
We will first give a brief background on micro aerial vehicles (MAV), the opportunities they offer, and the challenges they present, followed by an introductory overview on the insect-scale MAV prototype called RobeBee, which is currently under our development to demonstrate autonomous flight. Next, we will dive into the detailed implementation of its electronic control system and elaborate the reliability concerns and considerations in our design. Improved performance and reliability have been confirmed in both simulation and experiment after applying codesign strategy between supply regulation and clock generation. Finally, we will conclude with our vision on the future of MAV from a reliability perspective.
2 BACKGROUND OF MICRO AERIAL VEHICLE
2.1 WHAT IS MAV?
Unmanned aerial vehicle technology has indeed taken off and its tremendous commercial success and wide adoption in many fields has also fueled increasing recent interest in MAV, which loosely refer to air craft with size less than 15 cm in length, width, or height and weigh less than 100 g. These systems are envisioned for applications including reconnaissance, hazardous environment exploration, and search-and-rescue, and therefore may require various morphologies that can be broken into a number of classes such as fixed wing, flapping wing, or rotary wing.
The history of MAV dates back to 1997, when the United States Defense Advanced Research Projects Agency (DARPA) announced its “micro air vehicle” program . The technology advances that propelled this bold marching step are the maturation of microsensors, the rapid evolution of microelectromechanical system, also known as MEMS, as well as the continued exponential improvement of computing technology. In 2005, DARPA again pushed the limits of aerial robotics by announcing its “nano air vehicle” program with tighter requirements of 10 g or less and within 7.5 cm dimension. These programs have led to successful MAV prototypes including Microbat , Nano Hummingbird , and inspired a number of recent commercially available flapping-wing toy ornithopters and RC helicopters on the scale of MAVs.
Taking the pursuit of miniaturization to the next level, researchers are now working on “pico” air vehicles that have a maximum takeoff mass of 500 mg or less and maximum dimension of 5 cm or less . As this size and weight range falls into the scale of most flying insects, it is no surprise that many successful MAV systems developed at this scale are modeled after insects. The Harvard RoboBee project, which is the focus of this chapter, is one example prototype of a “pico” air vehicle.
2.2 WHY MAV?
Why are we interested in the extreme art of building insect-scale MAVs? Rodney Brooks, a renowned roboticist, has put it quite eloquently in his forward-looking paper in 1989, titled “Fast, Cheap, and Out of Control: A Robot Invasion of the Solar System” , where he laid out the benefits of employing small robots for space exploration. Fast forward 25 years, rapid development in information technology and advanced manufacturing has pushed the applications of robots well beyond the space exploration missions, yet many of the same benefits Brooks argued in his seminal work remain:
Fast development and deployment time: it used to be that “big” complex systems take years of planning to take shape and the turnaround time to discover any critical problems in the system design can be prohibitive. Similarly, even after the system has been designed, developed, and debugged, its deployment can be equally time-consuming because of its complexity and the intricacies involved to interface it with other complex systems and humans. Therefore, only huge organizations, such as the military and government agencies, could afford the resources and man power required for such missions over an extended period of time, which severely limited the adoption of the traditional large-scale robotic technology. As we miniaturize robots to the microscale by leveraging established design methodology from the IC industry and development practices from software engineering, the time it takes from conception to implementation of the robotic system can be drastically reduced, resulting in faster design iterations and ultimately superior system performance and reliability.