Design, Analysis and Experiments of a High-Speed Water Hovering Amphibious Robot: AmphiSTAR

Avi Cohen
PhD student
Ben Gurion University of the Negev, Israel
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This research details the development, modeling, and performance of AmphiSTAR, a novel high-speed amphibious robot. AmphiSTAR is a “wheeled” robot fitted with propellers at its bottom that allow it to crawl on the ground and hover on the water at high speeds. Two members of the animal kingdom inspire the AmphiSTAR. It possesses a sprawling mechanism inspired by cockroaches and is designed to “run” on the water at high speeds like the Basilisk lizard. The experimental robot can crawl over the ground with performances similar to the original STAR robots and attain speeds of 3.6 m/s. The robot can run continuously on water surfaces at speeds of 1.5 m/s. It can also swim (i.e., float while advancing by rotating its propellers) at low speeds and transition from swimming to crawling.
We develop a theoretical model of the lift force as a function of the rotational speed of partially submerged propellers whose axes are vertical. Using blade element theory, we present a simplistic approach to calculate the lift force and compare this to the pressure the robot applies on the water’s surface, calculated as the displaced water volume. The displaced water volume is approximated as the height of the displaced water multiplied by the surface area of the propeller. We also estimated the robot’s stability when hovering over the water in the roll and pitch directions and experimentally validated the results. Finally, we developed a new experimental setup to validate our experiments for different parameter values and cases and estimate the thrust and lift forces that the robot can generate. At very high rotational speeds, the lift force converges with the weight, which is the total propeller volume.