Crawl and Fly: A Bio-Inspired Robot Utilizing Unified Actuation for Hybrid Aerial-Terrestrial Locomotion

This letter details the design and validation of a legged terrestrial locomotion system integrated onto a hummingbird-scale flapping wing robot. Two pairs of legs powered by the flight actuators allow forward, reverse, and steering motions while on the ground. Through controlled sinusoidal drive signals, this mechanically simple locomotion system allows the robot to crawl through small gaps about half the height of spaces through which it could fly thanks to the robot's transition from a vertical to horizontal orientation when crawling. On smooth hard surfaces, the robot is capable of crawling at 100 mm/s. Gaining a terrestrial mode of movement not only expands its locomotion strategies and environmental adaptability, but it also improves the endurance of the robot in particular missions due to the low power consumption. A unique design principle is that the flight components of the robot are unchanged from the original aerial robot design, and terrestrial locomotion is realized with the addition of two capstan-interlinked pairs of legs constructed from 3D printed plastic and carbon fiber rods. Based on the dual use of the flight actuators, the robot experimentally demonstrated sustained hybrid aerial-terrestrial locomotion as well as smooth crawl-to-fly transition.