Characterization of running with compliant curved legs

Abstract

Running with compliant curved legs involves the progression of the center of pressure, the changes of both the leg's stiffness and effective rest length, and the shift of the location of the maximum stress point along the leg. These phenomena are product of the geometric and material properties of these legs, and the rolling motion produced during stance. We examine these aspects with several reduced-order dynamical models to relate the leg's design parameters (such as normalized foot radius, leg's effective stiffness, location of the maximum stress point and leg shape) to running performance (such as robustness and efficiency). By using these models, we show that running with compliant curved legs can be more efficient, robust with fast recovery behavior from perturbations than running with compliant straight legs. Moreover, the running performance can be further improved by tuning these design parameters in the context of running with rolling. The results shown in this work may serve as potential guidance for future compliant curved leg designs that may further improve the running performance.

Fundamentals of soft robot locomotion

“…This simple model effectively describes the locomotion of a great variety of different animals (including humans) that use running and hopping gaits [34], and has been successfully translated into several robotic prototypes. Straightforward replicas of compressible legs have employed pneumatic elements [35] or elastic springs [36,37], whereas more elaborate designs have used flexible structural elements [38,39], a C-shaped foot [40,41], bow-like legs [42] or springs that mimic muscle-tendon systems [43]. Similar to multi-legged animals [34], multi-legged robots could base their locomotion on the SLIP model by considering the equivalent contribution of parallel springs [44], so that the system is considered to have a single virtual leg.…”

Evolving optimal learning strategies for robust locomotion in the spring-loaded inverted pendulum model

“…21,22 Some work has investigated how the shape of the leg can be used to achieve variable stiffness and relative leg length changes during the stance phase. 23,24 Similarly, Owaki et al…”

“…21,22 Some work has investigated how the shape of the leg can be used to achieve variable stiffness and relative leg length changes during the stance phase. 23,24 Similarly, Owaki et al investigated different nonlinear stiffness functions and identified the ones that are beneficial, 25 although this was done using a compass gate, rather than the SLIP model. Andrews et al explored changing the length of the spring, rather than its stiffness in their work.…”

A torque-actuated dissipative spring loaded inverted pendulum model with rolling contact and its use as the template for design and dynamic behavior generation on a hexapod robot

“…The spring constant is chosen according to the optimal variable table from our previous research [13]. The damping coefficient is chosen from the existing spring damping ratio in [15] with its several multiples. The damper is designed by using the principle of a coaxial rotating cylinder viscometer [16,17].…”