Comparison of the relationship between pectoral-fin movement and fin shape based on force index for fish-type balloon robot

Balloon robots consist of a balloon body, which is filled with helium to provide buoyancy. In particular, fish-type balloon robots (FBRs) incorporate caudal- and pectoral-fin motions as their propulsion mechanism, which can be combined to realize complex motions. However, the propulsive force generated by the pectoral-fin motion is less, which is a disadvantage, and it is necessary to increase the propulsive force. Since the weight of FBR is limited, it is crucial to select a fin that can generate larger propulsive force at the same weight. In this study, pectoral fins with different shapes and materials are developed, and the propulsive force generated by various fin movements is measured. Finally, the results are compared and discussed relative to the influence of shape and softness on the propulsion.