Towards Bipedal Behavior on a Quadrupedal Platform Using Optimal Control

This paper explores the applicability of a Linear Quadratic Regulator (LQR) controller design to the problem of bipedal stance on the Minitaur [1] quadrupedal robot. Restricted to the sagittal plane, this behavior exposes a three degree of freedom (DOF) double inverted pendulum with extensible length that can be projected onto the familiar underactuated revolute-revolute “Acrobot” model by assuming a locked prismatic DOF, and a pinned toe. While previous work has documented the successful use of local LQR control to stabilize a physical Acrobot, simulations reveal that a design very similar to those discussed in the past literature cannot achieve an empirically viable controller for our physical plant. Experiments with a series of increasingly close physical facsimiles leading to the actual Minitaur platform itself corroborate and underscore the physical Minitaur platform corroborate and underscore the implications of the simulation study. We conclude that local LQR-based linearized controller designs are too fragile to stabilize the physical Minitaur platform around its vertically erect equilibrium and end with a brief assessment of a variety of more sophisticated nonlinear control approaches whose pursuit is now in progress

Laboratory on Legs: An Architechture for Adjustable Morphology with Legged Robots

For mobile robots, the essential units of actuation, computation, and sensing must be designed to fit within the body of the robot. Additional capabilities will largely depend upon a given activity, and should be easily reconfigurable to maximize the diversity of applications and experiments. To address this issue, we introduce a modular architecture originally developed and tested in the design and implementation of the X-RHex hexapod that allows the robot to operate as a mobile laboratory on legs. In the present paper we will introduce the specification, design and very earliest operational data of Canid, an actively driven compliant-spined quadruped whose completely different morphology and intended dynamical operating point are nevertheless built around exactly the same “Lab on Legs” actuation, computation, and sensing infrastructure. We will review as well, more briefly a second RHex variation, the XRL latform, built using the same components. For more information: Kod*La

Effects of Hip and Ankle Moments on Running Stability: Simulation of a Simplified Model

In human running, the ankle, knee, and hip moments are known to play different roles to influence the dynamics of locomotion. A recent study of hip moments and several hip-based legged robots have revealed that hip actuation can significantly improve the stability of locomotion, whether controlled or uncontrolled. Ankle moments are expected to also significantly affect running stability, but in a different way than hip moments. Here we seek to advance the current theory of dynamic running and associated legged robots by determining how simple open-loop ankle moments could affect running stability. We simulate a dynamical model, and compare it with a previous study on the role of hip moments. The model is relatively simple with a rigid trunk and a springy leg to represent the effective stiffness of the knee. At the hip we use a previously established proportional and derivative controlled moment with pitching angle as feedback. At the ankle we use the simplest ankle actuation, a constant ankle torque as a rough approximation of the net positive work done by the ankle moment during human locomotion. Even in this simplified model, we find that ankle and hip moments can affect the center of mass (COM) and pitching dynamics in distinct ways. Analysis of the governing equations shows that hip moments can directly influence the upper body balance, as well as indirectly influence the center of mass translation dynamics. However, ankle moments can only indirectly influence both. Simulation of the governing equations shows that the addition of ankle moment has significant benefits to the quality of locomotion stability, such as a larger basin of attraction. We also find that adding the ankle moments generally expands the range of parameters and velocities for which the model displays stable solutions. Overall, these findings suggest that ankle moments would play a significant role in improving the quality and range of running stability in a system with a rigid trunk and a telescoping leg, which would be a natural extension of current springy leg robots. Further, these results provide insights into the role that ankle moments might play in human locomotion

X-RHex: A Highly Mobile Hexapedal Robot for Sensorimotor Tasks

We report on the design and development of X-RHex, a hexapedal robot with a single actuator per leg, intended for real-world mobile applications. X-RHex is an updated version of the RHex platform, designed to offer substantial improvements in power, run-time, payload size, durability, and terrain negotiation, with a smaller physical volume and a comparable footprint and weight. Furthermore, X-RHex is designed to be easier to build and maintain by using a variety of commercial off-the-shelf (COTS) components for a majority of its internals. This document describes the X-RHex architecture and design, with a particular focus on the new ability of this robot to carry modular payloads as a laboratory on legs. X-RHex supports a variety of sensor suites on a small, mobile robotic platform intended for broad, general use in research, defense, and search and rescue applications. Comparisons with previous RHex platforms are presented throughout, with preliminary tests indicating that the locomotive capabilities of X-RHex can meet or exceed the previous platforms. With the additional payload capabilities of X-RHex, we claim it to be the first robot of its size to carry a fully programmable GPU for fast, parallel sensor processing

Template-based control of the bipedal robot ATRIAS

This thesis details the derivation and application of template-based controls on a bipedal robot, as well as a description of the software framework that enabled experimentation. The software framework uses a combination of open-source tools including ROS, OROCOS, EtherCAT, and Xenomai to create a real-time environment for the controllers. The first controller makes the robot (ATRIAS) walk as if it was the Spring Loaded Inverted Pendulum (SLIP) model. This demonstrates that ATRIAS, which was designed to be as close to the SLIP model as possible, can behave similarly to the reduced-order model. While the first controller is implemented with a torso that is mechanically fixed in place, the second controller handles an unlocked torso, which adds another degree of freedom. This controller is implemented based on a Torso SLIP (TSLIP) reduced-order model. The controller imposes a Virtual Pivot Point (VPP) by redirecting ground reaction forces to a geometrically fixed point with respect to the torso above the center of mass. Using VPP control, ATRIAS is able to take up to 22 steps on its own without using other techniques to keep its torso upright or inject energy, and it is shown that the generated ground reaction forces are similar to those produced by the reduced-order model. These controllers demonstrate that SLIP-like reduced-order control methods can be implemented on ATRIAS, and are a promising avenue for further research

Моделювання динамічних процесів крокуючого робота

Магістерська дисертація містить модернізовану модель двоногого крокуючого робота. В роботі було вдосконалено існуючу авторську модель робота, збільшено її функціональні можливості, реалізовано логіку обходження перешкоди на шляху робота, створено програмний код для відслідковування динамічних процесів моделі робота та окремих його суглобів, досліджено та оптимізовано ефективність робота. Актуальність. Сучасний розвиток науки дозволяє проводити активні дослідження в області робототехніки з метою створення спеціалізованих двоногих роботів, котрі будуть асистувати людині у небезпечних середовищах або навіть повністю замінювати її. Тому задача розширення функціональних можливостей двоногих роботів для використання у небезпечних середовищах є досить цікавою, а її розв`язок –затребуваним. Метою магістерської дисертації єпідвищення функціональних можливостей існуючої моделі двоногого крокуючого робота.Об`єкт дослідження:модель двоногого крокуючого робота у середовищі MATLAB/Simulink.Предмет дослідження:моделювання динамічних процесів крокуючого робота.Наукова новизнаодержаних у магістерській дисертації результатів полягає у вдосконаленні функціональних можливостей існуючої моделі двоногого крокуючого робота, а саме –у реалізації логіки обходження моделлю робота завади на її шляху.Master's dissertation contains an upgraded model of a two-legged walking robot. The existing author's model of the robot was improved, its functionality was increased, the logic of bypassing the obstacle on the way of the robot was implemented, software code for tracking dynamic processes of the robot model and its joints was created, robot efficiency was determined and optimized. Relevance. Modern levelof science brings huge possibilitiesfor active research in the field of robotics in order to create specialized bipedal robots that will assist humanin dangerous environments or even completely replace himor her. Therefore, the task of expanding the functionality of bipedal robots for use in hazardous environments is quite interesting and topical.The purpose of the master's dissertation is to increase the functionality of the existing model of a two-legged walking robot.Object of research: modelof abipedal walking robotin MATLAB/Simulink environment.Subject of research: modelingof dynamic processes of a walking robot.The scientific novelty of the results obtained in the master's dissertation isimprovementof functionality of existingtwo-legged walking robot`smodel, namely -to implement the logic of the obstacle bypassing by the robot`s modelon it`spath

A bipedal running robot with one actuator per leg

Abstract- This paper presents experiments with a new, three-dimensional bipedal running behaviour for our Robotic Hexapod, RHex. The robot and the bipedal gait are underactuated, using only one actuated degree of freedom per compliant leg. We doubled up RHex's hind legs by attaching a duplicate set of hind legs at 180 ° , forming 'S ' shaped legs. This reduces the actuator speed requirements during non-contact, while preserving the bipedal dynamics and control challenges. Stable running at average speeds between 0.67 and 1.07 m/s with a success rate of 100 % over thirty runs is obtained with only leg angle and body orientation feedback. Index Terms – bipedal running, compliance, legged robot. I

A Foot Placement Strategy for Robust Bipedal Gait Control

This thesis introduces a new measure of balance for bipedal robotics called the foot placement estimator (FPE). To develop this measure, stability first is defined for a simple biped. A proof of the stability of a simple biped in a controls sense is shown to exist using classical methods for nonlinear systems. With the addition of a contact model, an analytical solution is provided to define the bounds of the region of stability. This provides the basis for the FPE which estimates where the biped must step in order to be stable. By using the FPE in combination with a state machine, complete gait cycles are created without any precalculated trajectories. This includes gait initiation and termination. The bipedal model is then advanced to include more realistic mechanical and environmental models and the FPE approach is verified in a dynamic simulation. From these results, a 5-link, point-foot robot is designed and constructed to provide the final validation that the FPE can be used to provide closed-loop gait control. In addition, this approach is shown to demonstrate significant robustness to external disturbances. Finally, the FPE is shown in experimental results to be an unprecedented estimate of where humans place their feet for walking and jumping, and for stepping in response to an external disturbance