A comprehensive review of driving mechanisms in amphibian spherical robots

A spherical robot is based on the rolling concept inspired by the pangolins. This mode of locomotion is faster and safer as its spherical body becomes a protective shield. The mobility, adaptability, and concealment provided by a spherical robot can be used for terrestrial, aquatic, and amphibious applications such as harbour patrolling, defence tasks, rough terrains exploration, and agriculture. In designing the robot, priority on the centre of gravity position should be given as this will affect the robot’s stability, either while static or in motion. A proper driving principle can overcome this issue while ensuring that the robot can perform a given task. Therefore, this paper intends to identify the driving principle proposed for spherical amphibian robots by systematically reviewing existing driving methods and the mechanisms used. From the search, 159 titles were published since 2015. The review has identified that the driving mechanism of a spherical amphibian robot depends on the actuation method, which is the legged actuation, combined actuation, and linear actuation. Each driving principle has its trade-off in performing the terrestrial and underwater motion. Furthermore, the driving principle also affects the advantages of a spherical robot system. Hence, studies on the driving principle that are more agile and do not ignore the spherical robot’s main advantage need to be given emphasis.