Amphibious Robotic Propulsive Mechanisms: Current Technologies and Open Challenges

Amphibious robots capable of transition from aquatic to terrestrial locomotion face significant challenges associated with propulsive efficacy in each environment. Conventionally, amphibious robots have utilized separate systems for aquatic and terrestrial locomotion, such as rotors and wheels, respectively. Recent approaches have attempted to consolidate the propulsive mechanism footprint and complexity in hopes of creating systems that mirror the performance and adaptability of living organisms. The crux of such a bioinspired design philosophy lies in integrating hydrodynamic profiles and terrestrial mobility, two seemingly antithetical features, into a cohesive robot architecture. State-of-the-art amphibious robots approach this challenge in a variety of ways and can be sorted into four distinct categories based on their locomotion mechanisms and body plans: (1) wheeled, (2) legged, (3) undulating, and (4) soft. This chapter surveys existing amphibious robots under each category, identifies seminal designs, and briefly examines them. We then synthesize findings from the survey to highlight open avenues of research for the continued development of amphibious robots. Lastly, we discuss our ongoing research developing a variable stiffness morphing limb as a potential next-generation propulsor for amphibious robots.