Design of a Tunable Stiffness Composite Leg for Dynamic Locomotion

Abstract

Passively compliant legs have been instrumental in the development of dynamically running legged robots. Having properly tuned leg springs is essential for stable, robust and energetically efficient running at high speeds. Recent simulation studies indicate that having variable stiffness legs, as animals do, can significantly improve the speed and stability of these robots in changing environmental conditions. However, to date, the mechanical complexities of designing usefully robust tunable passive compliance into legs has precluded their implementation on practical running robots. This paper describes a new design of a "structurally controlled variable stiffness" leg for a hexapedal running robot. This new leg improves on previous designs' performance and enables runtime modification of leg stiffness in a small, lightweight, and rugged package. Modeling and leg test experiments are presented that characterize the improvement in stiffness range, energy storage, and dynamic coupling properties of these legs. We conclude that this variable stiffness leg design is now ready for implementation and testing on a dynamical running robot.

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.…”

Characterization of Dynamic Behaviors in a Hexapod Robot

“…Our long term goal is to develop a unified constructive approach to gait design where both the mechanical [44] and algorithmic aspects are considered in an integrated manner. Notwithstanding a decade's effort [35,[49][50][51], mathematical analysis that can account for the emergence of SLIP dynamics in RHex-style systems has proven challenging.…”

“…This architecture-an improved version of the setup in [37]-facilitates the necessary systematic data collection in controlled environmental conditions. EduBot (Figure 1(a)), whose variants have successfully served in a wide range of experimental robotics studies [1,37,38,44,45] and in classrooms [46], is a small form-factor legged mobility system that adopts the successful RHex morphology (Figure 1(b)) and task-level open-loop locomotion strategy [2]. The platform weights 3.31 kg.…”

New Variable Passive-Compliant Element Design for Quadruped Adaptation to Stiffness-Varying Terrain

“…The design was later altered in [24] to obtain better properties. This approach shares some similarity with the approach presented in this paper.…”