Summary of the RHex robot platform

This page summarizes the RHex project by giving a brief history, outlining its latest capabilities, illustrated with images and videos and presents relevant publications and links for further inquiry

History

RHex project spawned from the DARPA CBS/CBBS program in 1998, funded with $5 million over 5 years. The first prototype was built by Uluc Saranli in 1999, followed by numerous revisions and improvements on the platform design and the algorithms. The following sequence of images shows the progress on the platform.


RP0 Prototype	RHex 0.8	RHex 0.9

Shelley	RHex 1.1 (with camera)	RHex 1.1 with Leg Sensors

Rugged RHex	Aqua	Wheel RHex

Towards the end of the project, 30 researchers from the following institutions took part in various aspects of research and development

The University of Michigan, Ann Arbor, MI
McGill University, Montreal, Canada
Carnegie Mellon University, Pittsburgh, PA
University of California, Berkeley, CA
Princeton University, Princeton, NJ
Cornell University, 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 underactuation and helps simplify mechanical design, yielding robustness
Sprawled posture, inspired from insects, results in passive stabilization of lateral motion
Control is open-loop at the gait level, but closed loop at the task level. Stability comes as a result of passive mechanics, not high-bandwidth 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 5 body lengths per second (just over 2.25m/s)
Climbing a wide range of stairs
Climbing slopes up to 45 degrees
Traverse obstacles as high as 20cm (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 30cm 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, camera and strain gauges 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

Despite this large list of capabilities, there are still numerous open problems within the RHex morphology. Firstly, the flexibility of its legged design leaves significant room for additional behaviors. Furthermore, its high mobility over natural terrain opens up new possibilities for specific application domains for which components to achieve autonomy are still in their infancy. Finally, commercialization of the RHex platform requires significant platform development as well as further behavioral research to improve its performance.

Movies


Fast running	Tumbling over rock field	Pronking

Bounding	Stair climbing	Hill climbing

Self-adjusting legs	Flipping	Bipedal running

Running in wheel mode	Pipe crossing	Surface swimming

Line following	Target tracking	Diving

Leaping	RHex on Wheels

Publications

[1]	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. [ bib \| .pdf ]
[2]	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. [ bib \| .pdf ]
[3]	U. Saranli, M. Buehler, and D. E. Koditschek. RHex: A simple and highly mobile robot. International Journal of Robotics Research, 20(7):616-631, July 2001. [ bib \| .pdf ]
[4]	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. [ bib \| .pdf ]
[5]	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. [ bib \| .pdf \| .ps.gz ]
[6]	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. [ bib \| .pdf ]
[7]	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. [ bib \| .pdf \| .ps.gz ]
[8]	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. [ bib \| .pdf \| .ps.gz ]
[9]	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. [ bib \| .pdf \| .ps.gz ]
[10]	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. [ bib \| .pdf ]
[11]	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. [ bib \| .pdf \| .ps.gz ]
[12]	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. [ bib \| .pdf \| .ps.gz ]
[13]	M. Buehler. Dynamic Locomotion and Energetics of RHex, a Six-Legged Robot. The Physiologist, 45(4):340, August 2002.
[14]	M. Buehler. Dynamic Locomotion with One, Four and Six-Legged Robots. Journal of the Robotics Society of Japan, 20(3):15-20, April 2002. [ .pdf ]
[15]	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. [ .pdf ]
[16]	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. [ .pdf ]
[17]	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). [ .pdf ]
[18]	D. Campbell, M. Buehler. Stair Descent in the Simple Hexapod 'RHex'. In Proceedings of the 2003 IEEE Int. Conf. on Robotics and Automation (ICRA). [ .pdf ]
[19]	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. [ .pdf ]
[20]	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. [ .pdf ]
[21]	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. [ .pdf ]
[22]	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. [ .pdf ]
[23]	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 [ .pdf ]
[24]	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 [ .pdf ]
[25]	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. [ .pdf ]
[26]	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. [ .pdf ]
[27]	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. [ .pdf ]
[28]	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. [ .pdf ]

People

Middle East Technical University

Faculty

Asst. Prof. Afşar Saranlı
Prof. Kemal Leblebicioglu
Asst. Prof. Yiğit Yazıcıoğlu

Graduate Students

Tülay Akbey
Murat Deniz Aykın
Orkun Oğucu
Yasemin Özkan
Ege Saygıner
Gülhan Serhat
Ferit Üzer
Mert Ankaralı

Bilkent University

Faculty

Asst. Prof. Uluç Saranlı

Graduate Students

Ömur Arslan
Akın Avcı
Sıtar Kortik
Cihan Özturk
Tuğba Yıldız

Past Schools and Researchers

The University of Michigan

Faculty

Prof. Daniel Koditschek

Postdoctoral Associates

Dr. Richard Altendorfer
Richard Groff

Graduate Students

Rahul Bagdia
Richard Groff
Kapil Jain
Haldun Komsuoğlu
Pei-Chun Lin
Gabriel Lopes
Joel Weingarten

Undergraduate Students

Joseph Raisanen
Katherine Scott

Engineers

Karen Coulter

McGill University

Faculty

Prof. Martin Buehler

Graduate Students

Don Campbell
Neil Neville

Project Scientists

Dave McMordie
Chris Prahacs
Aaron Saunders
Matthew Smith

University of California, Berkeley

Faculty

Prof. Robert Full

Postdoctoral Associates

Dr. Noah Cowan

Carnegie Mellon University

Faculty

Dr. Alfred Rizzi

Postdoctoral Associates

Dr. Uluç Saranlı

Graduate Students

Ravi Balasubramanian
G. Clark Haynes
Jonathan Hurst
David Maiwand
Sarjoun Skaff

Project Scientists

Ben Brown
Dr. Jay Gowdy
Dr. George Kantor