Underwater performance evaluation of an amphibious spherical mother robot

Various underwater microrobots were applied widely to underwater operations in narrow spaces in recent years. By having the compact structure, the robots had some limitations in locomotion velocity and enduring time. Hence, a mother-son robot cooperation system was proposed to solve these limitations. A novel amphibious spherical robot was designed as the mother robot to carry the microrobots as son robots for collaboration. The spherical mother robot consisted of a sealed hemispheroid, two openable quarter spherical shells, a plastic circular plate, a plastic shelf for carrying microrobots and four actuating units. Each unit was composed of a water jet propeller and two servo motors, each of which could rotate 90° in horizontal or vertical direction respectively. The robot could implement on-land locomotion, as well as underwater locomotion. In this paper, we developed the prototype mother robot and did the force analysis of the actuating system in horizontal direction and vertical direction. And plenty of underwater experiments of the robot in the semi-submerged state were conducted to evaluate the underwater performance, including the moving forward experiments in the moving forward experiments of the robot actuated by two main actuating units and four actuating units. From the results of the underwater experiments, we got a maximal moving forward velocity of 13.7 cm/s under the efficient actuating and a maximal rotating velocity of 64.3°/s under a duty of 100%.