This paper presents the addition of two models for added mass to the fluid-field spring-loaded inverted pendulum (FF-SLIP) Model for legged swimming. The relative ability of these models to capture the increased fluid forces due to virtual mass displacement is evaluated using a two-legged swimming robot, Tadpole. We show that a simple addition to our reduced-order model can predict fluid-leg interaction forces while remaining computationally efficient.

The seafloor is a complex environment and it is challenging to conduct detailed mapping, soil composition sampling, and habitat characterization missions in this benthic region. As a step toward overcoming these challenges, we present a quadruped robot capable of walking on the seafloor and maneuvering via midfluid swimming. SELQIE, the Seafloor Environment Legged Quadruped Intelligent Explorer, is capable of walking underwater at speeds up to$0.2 ~\mathrm{m} / \mathrm{s}$, swimming at over$0.16 ~\mathrm{m} / \mathrm{s}$, and transitioning between modes. We also introduce a path planning algorithm that can account for both swimming and walking gaits to efficiently navigate around or over obstacles, and demonstrate the robot executing such a multi-modal trajectory.

Legged animals have developed a variety of modes of locomotion to adapt to the diverse and unknown terrain challenges posed in the natural world. Legged robots, however, have been largely limited to specializing in one domain, with few that have endeavored to bridge the gap between two. In this work we present the Scansorial, Terrestrial, and Aquatic Robot Quadruped (STARQ), a novel legged robot capable of bridging three different domains with three modes of locomotion: walking, climbing, and swimming. In this study we describe model-based design techniques as well as design innovations that have made multimodal locomotion possible including waterproof hips for 2-DOF high torque legs, legs capable of effective power transmission in three modes, and bi-directionally compliant feet for walking and attaching to vertical surfaces. To demonstrate the robot's capabilities we present locomotion test data including speed and cost of transport in each of these domains. We also demonstrate the capability to transition from walking to swimming in a natural environment.