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On designing an active tail for legged robots: simplifying control via decoupling of control objectives

Steve W. Heim (Department of Mechanical and Process Engineering, Swiss Federal Institute of Technology in Zurich, Zurich, Switzerland)
Mostafa Ajallooeian (Biorobotics Laboratory (BIOROB), École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland)
Peter Eckert (Biorobotics Laboratory (BIOROB), École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland)
Massimo Vespignani (Biorobotics Laboratory (BIOROB), École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland)
Auke Jan Ijspeert (Biorobotics Laboratory (BIOROB), École Polytechnique Fédérale de Lausanne, Lausanne, Switzerland)

Industrial Robot

ISSN: 0143-991x

Article publication date: 16 May 2016

Abstract

Purpose

The purpose of this paper is to explore the possible roles of active tails for steady-state legged locomotion, focusing on a design principle which simplifies control by decoupling different control objectives.

Design/methodology/approach

A series of simple models are proposed which capture the dynamics of an idealized running system with an active tail. These models suggest that the overall control problem can be simplified and effectively decoupled via a proper tail design. This design principle is further explored in simulation using trajectory optimization. The results are then validated in hardware using a one degree-of-freedom active tail mounted on the quadruped robot Cheetah-Cub.

Findings

The results of this paper show that an active tail can greatly improve both forward velocity and reduce body-pitch per stride while adding minimal complexity. Further, the results validate the design principle of using long, light tails compared to shorter heavier ones.

Originality/value

This paper builds on previous results, with a new focus on steady-state locomotion and in particular deals directly with stance phase dynamics. A novel design principle for tails is proposed and validated.

Keywords

Acknowledgements

The authors would like to thank all the members of the BioRob lab for constructive conversations and feedback, as well as interns and students who helped carry out tests. In particular, the authors thank François Longchamp and Daniel Chapuis for their contribution in the hardware development, Daniel Renjewski for advice on stability analysis, Jesse van den Kieboom for his help with the PSO framework. They would also like to thank various friends and colleagues who proofread the manuscript and provided valuable feedback.

Funding was received from the European Community’s Seventh Framework Program (FP7/2007-2013 – Challenge 2 – Cognitive Systems, Interaction, Robotics; grant agreement number 248311 (AMARSi)) and from the Swiss National Science Foundation through the National Centre of Competence in Research Robotics.

Citation

Heim, S.W., Ajallooeian, M., Eckert, P., Vespignani, M. and Ijspeert, A.J. (2016), "On designing an active tail for legged robots: simplifying control via decoupling of control objectives", Industrial Robot, Vol. 43 No. 3, pp. 338-346. https://doi.org/10.1108/IR-10-2015-0190

Publisher

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Emerald Group Publishing Limited

Copyright © 2016, Emerald Group Publishing Limited