Power and paddle strokes in a robotic sea lion pectoral flipper

Sea lions have the potential to serve as an excellent model for unmanned underwater vehicle (UUV) technologies which must operate in high energy flows are transition from underwater swimming to terrestrial locomotion. Though investigations have been conducted to predict the mechanisms by which the sea lion produces forces during swimming in the power and paddle phases of its stroke, few, if any, devices have been developed to recreate their clapping gait and capture force data and experimentally observe these mechanics. This study explores how forces are produced by a robotic foreflipper when driven over a series of strokes which modify key parameters of these power and paddle phases and how swimming performance can be altered based on these modifications. It was found that increasing speed in the power stroke increases thrust production in both the power and paddle phases of the stroke while also increasing lateral forces by varying degrees depending on the compliance of the flipper. Increasing power stroke angle was detrimental in both phases when the velocity of the paddle stroke was standardized in all experiments, but standard duration paddle strokes did demonstrate some increase in thrust production for slightly higher power stroke angles, especially in the case of the stiffer flipper. These results demonstrate how sensitive forces can be to these small modifications and what considerations must be made in order to properly take advantage of this swimming gait in an engineered system.