Swimming and Walking of an Amphibious Robot With Fin Actuators

With the goal of automatic monitoring of environments along natural coastal areas and tidal flats, researchers designed and developed an amphibious robot equipped with fin actuators called "RT-I" that mimics the locomotion of both a tortoise and a sea turtle. Experiments were carried out using a forearm with 4 degrees of freedom, which can reproduce the walking motions of tortoises and sea turtles on sand, to evaluate the walking performances of a robotic tortoise and a robotic sea turtle. It was clarified that the arm for a robotic tortoise is more suitable for use on soil compared with the arm for a robotic sea turtle. The advantages of both sea turtles and tortoises were adopted in a robotic turtle, namely, the lift-based swimming mode sea turtles use and the quadrupedal locomotion tortoises use. The present amphibious robot consists of four main components: (i) leg units, (ii) a control unit pressure hull, (iii) a buoyancy adjusting device, and (iv) a fairing cover. To realize not only swimming motion with the combination of flapping, rowing, and feathering, but also tortoise-like walking motion, three motors were set up at the acromioclavicular joint using a differential gear mechanism to independently produce the three types of motion, and one motor was set up to produce elbow joint motion. A buoyancy-adjusting device was installed to realize walking on land and in water as well as swimming in shallow water. The swimming and walking performances of the amphibious robot in water were evaluated by measuring the forward swimming speed, backward swimming speed, speed of turning, and speed of descending vertically as the indexes of the maneuverability of the robotic turtle, and the walking speed and propulsive efficiency with the crawl gait for various walking patterns in still water and in waves.