H. Benjamin Brown

Experiments in Balance with a 3D One-Legged Hopping Machine

In order to explore the balance in legged locomotion, we are studying systems that hop and run on one springy leg. Pre vious work has shown that relatively simple algorithms can achieve balance on one leg for the special case of a system that is constrained mechanically to operate in a plane (Rai bert, in press; Raibert and Brown, in press). Here we general ize the approach to a three-dimensional (3D) one-legged machine that runs and balances on an open floor without physical support. We decompose control of the machine into three separate parts: one part that controls forward running velocity, one part that controls attitude of the body, and a third part that controls hopping height. Experiments with a physical 3D one-legged hopping machine showed that this control scheme, while simple to implement, is powerful enough to permit hopping in place, running at a desired rate, and travel along a simple path. These algorithms that control locomotion in 3D are direct generalizations of those in 2D, with surprisingly little additional complication.

Machines That Walk

This paper explores the notion that the control of dynamically stable legged systems that locomote in 3-space can be decomposed into a planar part and an extra-planar part. The planar part generates the large leg and body motions that raise and lower the legs to achieve stepping, that propel the system forward, and that maintain balance. The planar part of the control system deals only with 2D dynamics. The extra-planar part of the locomotion control system suppresses motion in those degrees of freedom that would cause deviation from the plane of motion. These degrees of freedom include roll of the body, yaw of the body, and translation perpendicular to the intended direction of travel.

Evidence for Spring Loaded Inverted Pendulum Running in a Hexapod Robot

This paper presents the first evidence that the Spring Loaded Inverted Pendulum (SLIP) may be “anchored” in our recently designed compliant leg hexapod robot, RHex. Experimentally measured RHex center of mass trajectories are fit to the SLIP model and an analysis of the fitting error is performed. The fitting results are corroborated by numerical simulations. The “anchoring” of SLIP dynamics in RHex offers exciting possibilities for hierarchical control of hexapod robots.

A rapidly deployable manipulator system

A rapidly deployable manipulator system combines the flexibility of reconfigurable modular hardware with modular programming tools, allowing the user to rapidly create and program a manipulator, which is custom-tailored for a given task. This article describes the main building blocks of such a system: a reconfigurable modular manipulator system (RMMS), modular and reusable control software, and a novel agent-based approach to task-based design of modular manipulators.

Dynamic Mobility with Single-Wheel Configuration

This paper presents a novel concept of mobility that provides dynamic stability and rapid locomotion. The concept, called Gyrover, is a single-wheel, gyroscopically stabilized robot that can be considered as a single wheel actuated by a spinning flywheel attached to a two-link manipulator at the wheel bearing and drive motor. The spinning flywheel acts as a gyroscope to stabilize the robot, and it can be tilted to achieve steering. This configuration conveys significant advantages over multiwheel, statically stable vehicles, including good dynamic stability and insensitivity to attitude disturbances, high maneuverability, low rolling resistance, ability to recover from falls, and amphibious capability. In this paper, the authors present the robot concept, three prototypes of the design, and system implementation. The authors study the robot’s nonholonomic constraints and the stabilizing effect of the flywheel on the system through simulation and experiments.

Control of the Gyrover: a single-wheel gyroscopically stabilized robot

The Gyrover is a single-wheel gyroscopically stabilized mobile robot developed at Carnegie Mellon University. An internal pendulum serves as a counter weight for a drive motor that causes fore/aft motion, while a large gyroscope on a tilt mechanism provides for lateral balance and steering actuation. In this paper, we develop a detailed dynamic model for the Gyrover and use this model in an extended Kalman filter to estimate the complete state. A linearized version of the model is used to develop a state feedback controller. The design methodology is based on a semi-definite programming procedure which optimizes the stability region subject to a set of linear matrix inequalities that capture stability and pole placement constraints. Finally, the controller design combined with the extended Kalman filter are verified on the robot prototype.

Control system of Self-Mobile Space Manipulator

Self-Mobile Space Manipulator (SM/sup 2/) is a simple, 5-DOF (degree-of-freedom), 1/3-scale, laboratory version of a robot designed to walk on the trusswork and other exterior surfaces of Space Station Freedom. It will be capable of routine tasks such as inspection, parts transportation, and simple maintenance procedures. The authors have designed and built the robot and gravity compensation system to permit simulated zero-gravity experiments. They have developed the control system for the SM/sup 2/ including control hardware architecture and operating system, control station with various interfaces, hierarchical control structure, multiphase control strategy for step motion, and various low-level controllers. The system provides operator-friendly real-time monitoring, and robust control for 3D locomotion movements of the flexible robot.<<ETX>>

Control of a two-degree-of-freedom lightweight flexible arm with friction in the joints

This article describes the design and control of a two-joint, two-link flexible arm. This flexible arm was built with very light links, has most of its mass concentrated at the tip and uses a special mechanical configuration to approximately decouple radial tip motions from angular tip motions. The lightweight design and decoupling maximize the efficiency of power transmitted to the load. An important problem when controlling lightweight flexible arms is the large Coulomb friction of the motors. A two-nested-loop multivariable controller is used to control the lightweight flexible arm with friction in the joints. The inner loop controls the position of the motors while the outer loop controls the tip position. The resolved acceleration method is generalized to control this flexible arm. The compliance matrix is used to model the oscillations of the structure and is included in the decoupling/linearizing term of this controller. Experimental results are presented.

Controlling a Motorized Marionette with Human Motion Capture Data

In this paper, we present a method for controlling a motorized, string-driven marionette using motion capture data from human actors and from a traditional marionette operated by a professional puppeteer. We are interested in using motion capture data of a human actor to control the motorized marionette as a way of easily creating new performances. We use data from the hand-operated marionette both as a way of assessing the performance of the motorized marionette and to explore whether this technology could be used to preserve marionette performances. The human motion data must be extensively adapted for the marionette because its kinematic and dynamic properties differ from those of the human actor in degrees of freedom, limb length, workspace, mass distribution, sensors, and actuators. The motion from the hand-operated marionette requires less adaptation because the controls and dynamics are a closer match. Both data sets are adapted using an inverse kinematics algorithm that takes into account marker positions, joint motion ranges, string constraints, and potential energy. We also apply a feedforward controller to prevent extraneous swings of the hands. Experimental results show that our approach enables the marionette to perform motions that are qualitatively similar to the original human motion capture data.

The ParkourBot - a dynamic BowLeg climbing robot

The ParkourBot is an efficient and dynamic climbing robot. The robot comprises two springy legs connected to a body. Leg angle and spring tension are independently controlled. The robot climbs between two parallel walls by leaping from one wall to the other. During flight, the robot stores elastic energy in its springy legs and automatically releases the energy to “kick off” the wall during touch down. This paper elaborates on the mechanical design of the ParkourBot. We use a simple SLIP model to simulate the ParkourBot motion and stability. Finally, we detail experimental results, from open-loop climbing motions to closed-loop stabilization of climbing height in a planar, reduced gravity environment.