Abstract
Since the propulsion mechanism in fluid using elastic fins like caudal fin and pectoral fin of fish is effective, many studies of elastic fin for propulsion in water and development of fish robot using elastic fin were carried out. However, the optimum elasticity of fin is not constant and changed by the movement task and environment, such as swimming speed. It is very difficult to exchange fins of different bending stiffness while moving. Thus, we aimed to develop real-time variable-stiffness fins. As the one of the variable-stiffness-fins, we have developed a fin with variable-effective-length spring. The apparent stiffness of the fin can be changed dynamically. This paper describes measurement of pitching torque of the fin, and efficiency for the thrust force.
