RoboFly: Towards Autonomous Flight of a Multimodal Insect-Scale Robot

Thesis (Ph.D.)--University of Washington, 2020Insect-sized robots have numerous applications due to their small size. For example, they can go into confined spaces where humans or larger robots cannot. These applications include gas leak detections in pipelines, search and rescue in disaster response, and crop monitoring for smart agriculture. Insect-sized flapping-wing robots draw inspiration from nature's tiny machines such as flies and bees. Earlier iterations of these robots have successfully demonstrated hovering flight. However, there are some limitations to their abilities. Prior designs consist of many discrete parts that need to be manually assembled under a microscope. There are also limitations to their locomotion abilities. These robots could not control their heading while hovering, making them infeasible for many applications involving heading control and steering. Also, these robots relied on external sources for control feedback. This dissertation proposes a re-design of insect-sized flapping-wing robots: the UW Robofly. The idea behind the re-design is a robot that compares better with its biological counterparts in terms of autonomy. Autonomy in micro-robots can be quantified in the following three terms, which can be given equal importance: 1) Mobility autonomy, 2) power autonomy, and 3) control autonomy. In terms of mobility autonomy, the Robofly can perform multimodal locomotion, which includes ground, water surface, and aerial locomotion. The robot can also perform open-loop landing because its center of mass is closer to the ground. The robot is also easy to fabricate since it uses a folding mechanism that decreases the number of discrete components. Although hovering does not require a robot to control its heading, it is crucial for various applications, including image capture and video recording. A re-designed version of the UW Robofly, Robofly-Expanded, shows the ability to steer and control its heading while hovering, making it the first at this scale to control all six degrees of freedom with only two actuators. For power autonomy, the Robofly can carry a PV cell and onboard power electronics. It became the first robot at this scale to achieve wireless liftoff as a result of the efforts in power autonomy at UW. Lastly, control autonomy, which aims for the robot to hover without the need for motion feedback from offboard sensors such as a motion capture arena, is addressed. The robot requires at least three sensors onboard to make it hover about a point in space without drifting away. The proposed sensors are as follows-- 1) a MEMS gyroscope for attitude control, 2) an IR time-of-flight range sensor for altitude control, and 3) an optical flow sensor for lateral motion control in space. While earlier research has demonstrated flights with an onboard gyroscope and IR time-of-flight sensors, this research goes a step further and include an optical flow sensor onboard. A short flight demonstrating the ability of the robot to use the optical flow sensor data for lateral motion feedback is also presented. The work presented here overcomes significant limitations in previous work, bringing insect-sized flapping-wing robots much closer to full autonomous functionality and mobility. Future work now primarily entails further sensor integration, devising a controllable high-voltage power supply, and incorporating a power collection and storage system