Locomotor transitions in the potential energy landscape-dominated regime

Abstract

To traverse complex three-dimensional terrain with large obstacles, animals and robots must transition across different modes. However, the most mechanistic understanding of terrestrial locomotion concerns how to generate and stabilize near-steady-state, single-mode locomotion (e.g. walk, run). We know little about how to use physical interaction to make robust locomotor transitions. Here, we review our progress towards filling this gap by discovering terradynamic principles of multi-legged locomotor transitions, using simplified model systems representing distinct challenges in complex three-dimensional terrain. Remarkably, general physical principles emerge across diverse model systems, by modelling locomotor–terrain interaction using a potential energy landscape approach. The animal and robots' stereotyped locomotor modes are constrained by physical interaction. Locomotor transitions are stochastic, destabilizing, barrier-crossing transitions on the landscape. They can be induced by feed-forward self-propulsion and are facilitated by feedback-controlled active adjustment. General physical principles and strategies from our systematic studies already advanced robot performance in simple model systems. Efforts remain to better understand the intelligence aspect of locomotor transitions and how to compose larger-scale potential energy landscapes of complex three-dimensional terrains from simple landscapes of abstracted challenges. This will elucidate how the neuromechanical control system mediates physical interaction to generate multi-pathway locomotor transitions and lead to advancements in biology, physics, robotics and dynamical systems theory.

Propelling and perturbing appendages together facilitate strenuous ground self-righting

“…for body pitch < −90°; the full landscape maybe visualized using data and code provided (Othayoth and Li, 2021).…”

“…A recent potential energy landscape approach to locomotor transitions (Othayoth et al, 2021(Othayoth et al, , 2020 provides a modeling framework to understand how propelling and perturbing appendages together contribute to strenuous ground self-righting. A previous study modeling ground self-righting of turtles in two dimensions (the transverse plane in which the body rolls) suggested that, when trapped in a gravitational potential energy well, modest kinetic energy from perturbing appendages (legs and neck) helps overcome the small potential energy barriers (Domokos and Várkonyi, 2008).…”

Stability and manoeuvrability in animal movement: lessons from biology, modelling and robotics

“…The problem of how multi-legged animals adapt their gaits depending on terrain properties is addressed by Othayoth et al . [ 13 ] in their study, ‘Locomotor transitions in the potential energy landscape-dominated regime’. They investigate ‘terradynamic’ principles of locomotor transitions, using simplified model systems representing distinct challenges in complex three-dimensional terrains, for instance squeezing through pillars and flexible beams, crossing gaps, going-over steps or self-righting after flipping over.…”

Propelling and perturbing appendages together facilitate strenuous ground self-righting

“…where m is the total mass of the animal or robot, g is gravitational acceleration, zCoM is center of mass height from the ground. To determine the robot's center of mass, we used a CAD model of the robot (Figures 2A, Because the animal or robot did not pitch backward significantly, in the figures we do not show landscape for body pitch < −90°; the full landscape maybe visualized using data and code provided (Othayoth and Li, 2021).…”

“…Data from (Li et al, 2019). A recent potential energy landscape approach to locomotor transitions (Othayoth et al, 2021(Othayoth et al, , 2020) 97 provides a modeling framework to understand how propelling and perturbing appendages together 98 contribute to strenuous ground self-righting. A previous study modeling ground self-righting of turtles in 99 two dimensions (the transverse plane in which the body rolls) suggested that, when trapped in a gravitational potential energy well, modest kinetic energy from perturbing appendages (legs and neck) helps overcome the small potential energy barriers (Domokos and Várkonyi, 2008).…”