Performance evaluation on land of an amphibious spherical mother robot

Various underwater microrobots were used widely to work in limited spaces in the last few years. However, for having compact structures, the robots had some limitations of locomotion velocity and enduring time. In order to solve these problems, we proposed a mother-son robot cooperation system. We designed a conceptual structure of a novel amphibious spherical robot as the mother robot to carry the microrobots as son robots for collaboration. The spherical mother robot was composed of a sealed hemispheroid, two openable quarter spherical shells, a plastic circular plate, a plastic shelf and four actuating units. Each unit consisted of a water jet propeller and two servo motors, each of which could rotate 90° in horizontal or vertical direction respectively. The robot could perform walking and rotating motions on land, as well as moving forward and backward, rotating, surfacing and diving motions in water. We developed the prototype mother robot and did the force analysis of each unit of the actuating system. Then we proposed three walking gaits for the robot and carried out the walking experiments on the tile floor to evaluate the performance of the walking motion, including stability and velocity. From the experimental results of walking and rotating motions, we got that under a frequency of 3.33 Hz in Gait 3 (duty factor β=0.67) we got a maximal walking velocity of 22.5 cm/s. Under a frequency of 1.56 Hz in Gait 2 (duty factor β=0.75), we achieved a maximal rotating velocity of 71.29 °/s.