Rhex
Encyclopedia
Autonomous robot
Autonomous robots are robots that can perform desired tasks in unstructured environments without continuous human guidance. Many kinds of robots have some degree of autonomy. Different robots can be autonomous in different ways...
hexapod
Hexapod (robotics)
A six-legged walking robot should not be confused with a Stewart platform, a kind of parallel manipulator used in robotics applications.A hexapod robot is a mechanical vehicle that walks on six legs. Since a robot can be statically stable on three or more legs, a hexapod robot has a great deal of...
robot
Robot
A robot is a mechanical or virtual intelligent agent that can perform tasks automatically or with guidance, typically by remote control. In practice a robot is usually an electro-mechanical machine that is guided by computer and electronic programming. Robots can be autonomous, semi-autonomous or...
with compliant legs and only one actuator
Actuator
An actuator is a type of motor for moving or controlling a mechanism or system. It is operated by a source of energy, usually in the form of an electric current, hydraulic fluid pressure or pneumatic pressure, and converts that energy into some kind of motion. An actuator is the mechanism by which...
per leg. It is the first documented autonomous legged machine to have exhibited general mobility (speeds at bodylengths per second) over general terrain (variations in level at bodyheight scale). RHex is presently capable of speeds exceeding five body lengths per second (2.7 m/s), negotiates a wide variety of rugged terrains over thousands of bodylengths (3700 m distance on one set of batteries), manages slopes exceeding 45 degrees, swims, and climbs stairs.
History
RHex arises from a multidisciplinary and multi-university DARPA funded effort in Computational Neuromechanics that applies mathematical techniques from dynamical systems theoryDynamical systems theory
Dynamical systems theory is an area of applied mathematics used to describe the behavior of complex dynamical systems, usually by employing differential equations or difference equations. When differential equations are employed, the theory is called continuous dynamical systems. When difference...
to problems of animal locomotion
Animal locomotion
Animal locomotion, which is the act of self-propulsion by an animal, has many manifestations, including running, swimming, jumping and flying. Animals move for a variety of reasons, such as to find food, a mate, or a suitable microhabitat, and to escape predators...
, and, in turn, seeks inspiration from biology in advancing the state of the art
State of the art
The state of the art is the highest level of development, as of a device, technique, or scientific field, achieved at a particular time. It also refers to the level of development reached at any particular time as a result of the latest methodologies employed.- Origin :The earliest use of the term...
of robotic systems.
The RHex project received $5 million over 5 years from the DARPA CBS/CBBS program in 1998, and an approximate additional $3 million from other grants, such as National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
grants.
The following Universities participated on the initial RHex project:
- The University of Michigan, Ann Arbor, MI
- McGill UniversityMcGill UniversityMohammed Fathy is a public research university located in Montreal, Quebec, Canada. The university bears the name of James McGill, a prominent Montreal merchant from Glasgow, Scotland, whose bequest formed the beginning of the university...
, Montreal, Canada - Carnegie Mellon UniversityCarnegie Mellon UniversityCarnegie Mellon University is a private research university in Pittsburgh, Pennsylvania, United States....
, Pittsburgh, PA - University of CaliforniaUniversity of CaliforniaThe University of California is a public university system in the U.S. state of California. Under the California Master Plan for Higher Education, the University of California is a part of the state's three-tier public higher education system, which also includes the California State University...
, Berkeley, CA - Princeton UniversityPrinceton UniversityPrinceton University is a private research university located in Princeton, New Jersey, United States. The school is one of the eight universities of the Ivy League, and is one of the nine Colonial Colleges founded before the American Revolution....
, Princeton, NJ - Cornell UniversityCornell UniversityCornell University is an Ivy League university located in Ithaca, New York, United States. It is a private land-grant university, receiving annual funding from the State of New York for certain educational missions...
, Ithaca, NY
Capabilities
Throughout its development, RHex acquired a large number of capabilities in its behavioral repertoire. In fact, it is the only robot that is capable of performing such a wide variety of behaviors as a single, autonomous robot. This performance is due to the significant amount of inspiration from the study of biological systems, leading to a number of principles underlying RHex's design.- The use of legs instead of wheels or tracks opens the way for a large number of behaviors
- Passive compliance in the legs overcomes limitations of underactuationUnderactuationUnderactuation is a technical term used in robotics and control theory to describe mechanical devices that have a lower number of actuators than degrees of freedom....
and helps simplify mechanical design, yielding robustness - Sprawled posture, inspired from insects, results in passive stabilization of lateral motion
- Control is open-loopOpen-loop controllerAn open-loop controller, also called a non-feedback controller, is a type of controller that computes its input into a system using only the current state and its model of the system....
at the gaitGaitGait is the pattern of movement of the limbs of animals, including humans, during locomotion over a solid substrate. Most animals use a variety of gaits, selecting gait based on speed, terrain, the need to maneuver, and energetic efficiency...
level, but closed loop at the task level. Stability comes as a result of passive mechanics, not high-bandwidthBandwidth (computing)In computer networking and computer science, bandwidth, network bandwidth, data bandwidth, or digital bandwidth is a measure of available or consumed data communication resources expressed in bits/second or multiples of it .Note that in textbooks on wireless communications, modem data transmission,...
active control
At the end of the project's five years, RHex was capable of performing the following, mostly open-loop behaviors
- Running on reasonably flat, natural terrain at speeds up to 6 body lengths per second (just over 2.7 m/s)
- Climbing a wide range of stairs
- Climbing slopes up to 45 degrees
- Traverse obstacles as high as 20 cm (about twice RHex's leg clearance)
- Continuously run for 45 minutes, covering up to 3 miles with an efficient gait
- Successfully traverse badly broken terrain with large rocks and obstacles
- Walk and run upside down
- Flip itself over to recover nominal body orientation
- Leaping across ditches up to 30 cm wide
- Support remote control from up to 150m distance
in addition to a number of behaviors that increasingly relied on feedback from sensors such as the onboard gyro
Gyroscope
A gyroscope is a device for measuring or maintaining orientation, based on the principles of angular momentum. In essence, a mechanical gyroscope is a spinning wheel or disk whose axle is free to take any orientation...
, camera and strain gauge
Strain gauge
A strain gauge is a device used to measure the strain of an object. Invented by Edward E. Simmons and Arthur C. Ruge in 1938, the most common type of strain gauge consists of an insulating flexible backing which supports a metallic foil pattern. The gauge is attached to the object by a suitable...
s on the legs.
- Perform autonomous stabilization of yaw heading while running using feedback from the gyro
- Autonomously follow a line on the ground without any operator control
- Perform simultaneous localization and mapping by using artificial landmarks scattered over natural terrain
- Locomote on only two legs using active pendulum stabilization
- Autonomously change the rest lengths of its leg springs
- Autonomously run systematic experiments to tune its running gaits
- Use inertial sensors in combination with leg strain gauges to accurately estimate its body pose
Versions
- RP0 Prototype
- RHex 0.8 - New 4-bar legs, electronics redesign
- RHex 0.9 - New half-circle legs
- SHelly - Included a waterproof fiber glass shell
- RHex 1.1 - Included a Firewire video camera for real timeReal-time computingIn computer science, real-time computing , or reactive computing, is the study of hardware and software systems that are subject to a "real-time constraint"— e.g. operational deadlines from event to system response. Real-time programs must guarantee response within strict time constraints...
image processingImage processingIn electrical engineering and computer science, image processing is any form of signal processing for which the input is an image, such as a photograph or video frame; the output of image processing may be either an image or, a set of characteristics or parameters related to the image... - RHex 1.1 - with Leg sensors - Included legs equipped with strain gauges and independent wirelessWirelessWireless telecommunications is the transfer of information between two or more points that are not physically connected. Distances can be short, such as a few meters for television remote control, or as far as thousands or even millions of kilometers for deep-space radio communications...
communication devices. - Rugged RHex- Waterproof aluminum shell, larger motors and larger battery. Developed by Mecheligent for military purposes. Now sold by Boston Dynamics Inc.
- Aqua 1.0 - Waterproof aluminum shell, legs replaced by hybrid leg/fin for swimming. Developed at McGill University
- Aqua 2.0 - Redesigned aluminum shell, increased depth rating, smaller displacement
- EduBot - Educational version developed at the University of Pennsylvania
Publications
- A. Greenfield, U. Saranli, and A. A. Rizzi. Solving models of controlled dynamic planar rigid-body systems with frictional contact. International Journal of Robotics Research. 24(11):911-931, 2005.
- U. Saranli, A. A. Rizzi, and D. E. Koditschek. Model-based dynamic self-righting maneuvers for a hexapedal robot. International Journal of Robotics Research, 23(9):903-918, September 2004.
- R. Altendorfer, N. Moore, H. Komsuoglu, M. Buehler, H. B. Brown Jr., D. McMordie, U. Saranli, R. J. Full, and D. E. Koditschek. RHex: A biologically inspired hexapod runner. Autonomous Robots, 11(3):207-213, 2001.
- R. Altendorfer, U. Saranli, H. Komsuoglu, D. E. Koditschek, Jr. H. B. Brown, M. Buehler, N. Moore, D. McMordie, and R Full. Evidence for spring loaded inverted pendulum running in a hexapod robot. In D. Rus and S. Singh, editors, Experimental Robotics VII, Lecture Notes in Control and Information Sciences, chapter 5, pages 291-302. Springer, December 2000.
- U. Saranli, A. A. Rizzi, and D. E. Koditschek. Multi-point contact models for dynamic self-righting of a hexapod robot. In Proceedings of the Sixth International Workshop on the Algorithmic Foundations of Robotics (WAFR '04), pages 75–90, Utrecht/Zeist, The Netherlands, July 2004.
- U. Saranli and D. E. Koditschek. Template based control of hexapedal running. In Proceedings of the IEEE International Conference On Robotics and Automation, volume 1, pages 1374-1379, Taipei, Taiwan, September 2003.
- U. Saranli and D. E. Koditschek. Back flips with a hexapedal robot. In Proceedings of the IEEE International Conference on Robotics and Automation, volume 3, pages 2209-2215, Washington, DC, May 2002.
- H. Komsuoglu, D. McMordie, U. Saranli, N. Moore, M. Buehler, and D. E. Koditschek. Proprioception based behavioral advances in a hexapod robot. In International Conference on Robotics and Automation, volume 4, pages 3650-3655, Seoul, Korea, 2001.
- M. Buehler, U. Saranli, D. Papadopoulos, and D. E. Koditschek. Dynamic locomotion with four and six legged robots. In Proceedings of the International Symposium on Adaptive Motion of Animals and Machines, August 2000.
- U. Saranli, M. Buehler, and D. E. Koditschek. Design, modeling and preliminary control of a compliant hexapod robot. In Proceedings of the IEEE International Conference On Robotics and Automation, volume 3, pages 2589-96, San Francisco, CA, USA, April 2000.
- U. Saranli, W. J. Schwind, and D. E. Koditschek. Toward the control of a multi-jointed, monoped runner. In Proceedings of the IEEE International Conference On Robotics and Automation, volume 3, pages 2676-82, New York, 1998.
- M. Buehler. Dynamic Locomotion and Energetics of RHex, a Six-Legged Robot. The Physiologist, 45(4):340, August 2002.
- M. Buehler. Dynamic Locomotion with One, Four and Six-Legged Robots. Journal of the Robotics Society of Japan, 20(3):15-20, April 2002.
- D. Campbell and M. Buehler. Preliminary Bounding Experiments in a Dynamic Hexapod. In Bruno Siciliano and Paolo Dario, editors, Experimental Robotics VIII, p. 612-621, Springer-Verlag, 2003.
- N. Neville, M. Buehler. Towards Bipedal Running of a Six Legged Robot. In Proceedings of the 12th Yale Workshop on Adaptive and Learning Systems, May 2003.
- D. McMordie, C. Prahacs, M. Buehler. Towards a Dynamic Actuator Model for a Hexapod Robot. In Proceedings of the 2003 IEEE Int. Conf. on Robotics and Automation (ICRA).
- D. Campbell, M. Buehler. Stair Descent in the Simple Hexapod 'RHex'. In Proceedings of the 2003 IEEE Int. Conf. on Robotics and Automation (ICRA).
- E. Z. Moore, D. Campbell, F. Grimminger, and M. Buehler. Reliable Stair Climbing in the Simple Hexapod 'RHex'. In Proceedings of the 2002 IEEE Int. Conf. on Robotics and Automation (ICRA) Vol 3, pp 2222–2227, Washington, D.C., U.S.A., May 11–15, 2002.
- M. Buehler. RePaC design and control: Cheap and fast autonomous runners. In Proceedings of the 4th Int. Conf. on Climbing and Walking Robots Karlsruhe, Germany, September 24–26 , 2001.
- D. McMordie and M. Buehler. Towards Pronking with a Hexapod Robot. In Proceedings of the 4th Int. Conf. on Climbing and Walking Robots Karlsruhe, Germany, September 24–26 , 2001.
- E.Z. Moore and M. Buehler. Stable Stair Climbing in a Simple Hexapod. In Proceedings of the 4th Int. Conf. on Climbing and Walking Robots Karlsruhe, Germany, September 24–26 , 2001.
- P.-C. Lin, H. Komsuoglu, D. E. Koditschek. Sensor Data Fusion for Body State Estimation for a Hexapod Robot with Dynamical Gaits. In Proc. IEEE Int. Conf. Robotics and Automation (ICRA), pp4744–4749, Barcelona, Spain, April 2005
- S. Skaff, A. Rizzi, H. Choset, P.-C. Lin. A Context-Based State Estimation Technique for Hybrid Systems. In Proc. IEEE Int. Conf. Robotics and Automation (ICRA), pp3935–3940, Barcelona, Spain, April 2005
- P.-C. Lin, H. Komsuoglu, D. E. Koditschek. Toward a 6 DOF Body State Estimator for a Hexapod Robot with Dynamical Gaits. In IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), pp2265–2270, Sendai, Japan. September 2004.
- P.-C. Lin, H. Komsuoglu, D. E. Koditschek. Legged Odometry from Body Pose in a Hexapod Robot. In IFRR 9th International Symposium on Experimental Robotics (ISER), Singapore. June 2004.
- P.-C. Lin, H. Komsuoglu, D. E. Koditschek. A Leg Configuration Sensory System for Dynamical Body State Estimates in a Hexapod Robot. In Proc. IEEE Int. Conf. Robotics and Automation (ICRA), pp1391–1396, Taipei, Taiwan, September 2003.
- S. Skaff, G.A. Kantor, D. Maiwand, and A.A. Rizzi. Inertial navigation and visual line following for a dynamical hexapod robot. In Proc. of 2003 IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS), Vol 2, pp808–1813, October 2003.
- J.C. Spagna, D.I. Goldman, P-C. Lin, D.E. Koditschek, & R.J. Full. Distributed mechanical feedback in arthropods and robots simplifies control of rapid running on challenging terrain. Bioinspiration and Biomimetics 2: 9-18. January 2007.