Rate-independent soft crawlers

This paper applies the theory of rate-independent systems to model the locomotion of bio-mimetic soft crawlers. We prove the well-posedness of the approach and illustrate how the various strategies adopted by crawlers to achieve locomotion, such as friction anisotropy, complex shape changes and control on the friction coefficients, can be effectively described in terms of stasis domains. Compared to other rate-independent systems, locomotion models do not present any Dirichlet boundary condition, so that all rigid translations are admissible displacements, resulting in a non-coercivity of the energy term. We prove that existence and uniqueness of solution are guaranteed under suitable assumptions on the dissipation potential. Such results are then extended to the case of time-dependent dissipation

A study of snake-like locomotion through the analysis of a flexible robot model

We examine the problem of snake-like locomotion by studying a system consisting of a planar inextensible elastic rod with adjustable spontaneous curvature, which provides an internal actuation mechanism that mimics muscular action in a snake. Using a Cosserat model, we derive the equations of motion in two special cases: one in which the rod can only move along a prescribed curve, and one in which the rod is constrained to slide longitudinally without slipping laterally, but the path is not fixed a priori (free-path case). The second setting is inspired by undulatory locomotion of snakes on flat surfaces. The presence of constraints leads in both cases to non-standard boundary conditions that allow us to close and solve the equations of motion. The kinematics and dynamics of the system can be recovered from a one-dimensional equation, without any restrictive assumption on the followed trajectory or the actuation.We derive explicit formulae highlighting the role of spontaneous curvature in providing the driving force (and the steering, in the free-path case) needed for locomotion. We also provide analytical solutions for a special class of serpentine motions, which enable us to discuss the connection between observed trajectories, internal actuation and forces exchanged with the environment

What the hell do they mean by 'locomotion'?

In current mechanics literature one very frequently encounters the concepts locomotion and locomotion system. Unfortunately, strong definitions of these seemingly intuitively clear notions are generally missing. The following paper tries to fill this gap

An Adaptable Robotic Snake using a Compliant Actuated Tensegrity Structure for Locomotion and its Motion Pattern Analysis

The thesis explores the possibilities that using a compliant actuated tensegrity structure to build an adapted robotic snake for locomotion. With the development of modern society, people are relying more and more on robots to assist in their work. The robotic snake is a type of robot that is often used in exploration and relief work on complex terrain due to its unique bionic structure. However, traditional snake-like robots have structures that focus on specific snake-like movement patterns, but cannot actually simulate how the spine and muscles of a snake can work, thus losing out on desirable features such as high energy efficiency and flexibility. In this work, a tensegrity structure is researched to enable a robotic snake to realize the structure and capabilities of a snake. A prototype has been built for experiments: three segments connected by springs and strings which forms a tension network. The prototype is actuated by the change of the tension within the network, just as the muscles in a snake contract and stretch around the spine. Experiments with the prototype show that it can carry out effective rectilinear movement and steering movement on a variety of terrain, and its overall speed is mainly limited by the friction coefficient of the ground. However, because the underside of the body module prevents the module from tilting, the prototype cannot perform serpentine movement. More improvements in the shape design of the body modules and motion control could also be studied in future work

The role of functional surfaces in the locomotion of snakes

Snakes are one of the world’s most versatile organisms, at ease slithering through rubble or climbing vertical tree trunks. Their adaptations for conquering complex terrain thus serve naturally as inspirations for search and rescue robotics. In a combined experimental and theoretical investigation, we elucidate the propulsion mechanisms of snakes on both hard and granular substrates. The focus of this study is on physics of snake interactions with its environment. Snakes use one of several modes of locomotion, such as slithering on flat surfaces, sidewinding on sand, or accordion-like concertina and worm-like rectilinear motion to traverse crevices. We present a series of experiments and supporting mathematical models demonstrating how snakes optimize their speed and efficiency by adjusting their frictional properties as a function of position and time. Particular attention is paid to a novel paradigm in locomotion, a snake’s active control of its scales, which enables it to modify its frictional interactions with the ground. We use this discovery to build bio-inspired limbless robots that have improved sensitivity to the current state of the art: Scalybot has individually controlled sets of belly scales enabling it to climb slopes of 55 degrees. These findings will result in developing new functional materials and control algorithms that will guide roboticists as they endeavor towards building more effective all-terrain search and rescue robots.Ph.D