Exploring Batteryless UAVs by Mimicking Bird Flight

We demonstrate the first flight of battery-free, energy harvesting, and small-sized Unmanned Aerial Vehicle (UAV). UAVs' flight times are severely constrained due to being forced to navigate the tradeoff between battery energy storage and weight. Even for UAVs that recharge their batteries mid-flight, eventually, the batteries must be replaced. We explore a new paradigm of UAVs that can survive entirely off energy harvested from the sun. These UAVs store energy momentarily in small super-capacitors before using that energy to create lift. By removing the requirement for battery recharging and replacement, these UAVs can provide extended flight times and open up new applications. Unfortunately, the design space for these UAVs is complex and interdependent. Materials, wing structure, UAV type, motor and harvester efficiency, environmental effects, and many other things significantly affect the aircraft's performance. We engage in a principled design space exploration of various UAV designs to reach battery-free mechanical flight. We explore and test multiple prototypes before landing on an ornithopter-like UAV with a solar rack on top and a single BLDC motor. We then perform the first flight of a battery-free ornithopter. This is the first work to explore zero maintenance long-term flight for small craft and could enable numerous new applications that require large-scale, sustained aircraft flight, such as wildfire monitoring, smart agriculture, and urban air quality assessment.