Heterogeneous Leg Stiffness and Roll in Dynamic Running

Legged robots are by nature strongly non-linear, high-dimensional systems whose full complexity permits neither tractable mathematical analysis nor comprehensive numerical study. In consequence, a growing body of literature interrogates simplified “template” [1], [2] models—to date almost exclusively confined to sagittal- or horizontal-plane motion—with the aim of gaining insight into the design or control of the far messier reality. In this paper we introduce a simple bounding-in-place (“BIP”) model as a candidate frontal plane template for straight-ahead level ground running and explore its use in formulating hypotheses about whether and why rolling motion is important in legged locomotion. Numerical study of left-right compliance asymmetry in the BIP model suggests that compliance ratios yielding lowest steady state roll suffer far longer disturbance recovery transients than those promoting greater steady state roll. We offer preliminary experimental data obtained from video motion capture data of the frontal plane disturbance recovery patterns of a RHex-like hexapod suggesting a correspondence to the conclusions of the numerical study. Fig. 1. EduBot [19], a RHex-like [20] hexapedal robot. Jonathan Clark was supported by the IC Postdoctoral Fellow Program under grant number HM158204-1-2030. Samuel Burden was supported by the SUNFEST REU program at the University of Pennsylvania. This work was also partially supported by the NSF FIBR grant #0425878. For more information: Kod*La

Master of Science

thesisThis research studies the passive dynamics of an under-actuated trotting quadruped. The goal of this project is to perform three-dimensional (3D) dynamic simulations of a trotting quadruped robot to find proper leg configurations and stiffness range, in order to achieve stable trotting gait. First, a 3D simulation framework that includes all the six degrees of freedom of the body is introduced. Directionally compliant legs together with different leg configurations are employed to achieve passive stability. Compliant legs passively support the body during stance phase and during flight phase a motor is used to retract the legs. Leg configurations in the robot's sagittal and frontal plane are introduced. Numerical experiments are conducted to search the design space of the leg, focusing on increasing the passive stability of the robot. Increased stability is defined as decreased pitching, rolling, and yawing motion of the robot. The results indicate that optimized leg parameters can guarantee passive stable trotting with reduced roll, pitch, and yaw. Studies suggest that a quadruped robot with compliant legs is dynamically stable while trotting. Results indicate that the robot based on a biological model (i.e., caudal inclination of humeri and cranial inclination of femora) has the best performance. Stiff springs at hips and shoulders, soft spring at knees and elbows, and stiff springs at ankles and wrists are recommended. The results of this project provide a conceptual framework for understanding the movements of a trotting quadruped

REAL-TIME COMPUTER CONTROL OF A PROTOTYPE BIPEDAL SYSTEM

While much work in the area of robotics has attempted to replicate the power and agility of biological locomotion in a physical system, even the most impressive prototypes to date are functionally very simple in comparison to their biological counterparts. Biological systems particularly excel in their performance of dynamic maneuvers, such as a run or a jump. These maneuvers require explosive leg power coupled with sudden changes in trajectory. In mechanical systems, these requirements create the need for high-performance actuation and fast real-time control. Through a fusion of biologically inspired design and intelligent control strategies, current work aims to perform these types of maneuvers on a prototype biped robot named KURMET. As part of this research thrust, the goal of this work was to establish real-time control for the bipedal system. A distributed control system, that uses a cutting edge motion controller in conjunction with a Linux host computer, was developed to control these maneuvers. The resulting system provides on-board real-time control capable of 1~kHz servo rates over the biped's four actuators. A distributed control framework was developed to interface this foundational control system with the Linux host. This framework was then applied to produce state-based control strategies which have demonstrated a walk and a high-performance jump in hardware. While applied to these two complex movements, the control framework's modular design facilitates extension to a wide range of motions. Thus, this work has laid the foundation for a rich set of investigations into dynamic maneuvers for this platform.Grant No. IIS-0535098 from the National Science FoundationNo embarg