Models of benthic bipedalism

TL;DR

This paper presents a theoretical model and robotic implementation of aquatic bipedal walking, revealing bistable gaits with different energetic costs, and offers insights into the evolution and design of efficient walking systems.

Contribution

It introduces a minimal theoretical model of aquatic walking predicting bistable gaits and validates it with a biomimetic robot, advancing understanding of aquatic locomotion.

Findings

The model predicts undulatory and bistable gait patterns.

Robotic experiments confirm gait bistability and transition dynamics.

The study provides insights into physical constraints on walking evolution.

Abstract

Walking is a common bipedal and quadrupedal gait and is often associated with terrestrial and aquatic organisms. Inspired by recent evidence of the neural underpinnings of primitive aquatic walking in the little skate Leucoraja erinacea, we introduce a theoretical model of aquatic walking that reveals robust and efficient gaits with modest requirements for body morphology and control. The model predicts undulatory behavior of the system body with a regular foot placement pattern which is also observed in the animal, and additionally predicts the existence of gait bistability between two states, one with a large energetic cost for locomotion and another associated with almost no energetic cost. We show that these can be discovered using a simple reinforcement learning scheme. To test these theoretical frameworks, we built a bipedal robot and show that its behaviors are similar to those of our minimal model: its gait is also periodic and exhibits bistability, with a low efficiency gait separated from a high efficiency gait by a "jump" transition. Overall, our study highlights the physical constraints on the evolution of walking and provides a guide for the design of efficient biomimetic robots.