Eur. Phys. J. B 47, 161-164 (2005)
https://doi.org/10.1140/epjb/e2005-00302-5

Purcell's “rotator”: mechanical rotation at low Reynolds number

¹ Laboratoire Colloïdes et Matériaux Divisés, ESPCI et CNRS, UMR7612, UPMC, 10 rue Vauquelin, 75231 Paris Cedex 05, France
² Permanent Address: Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA

Corresponding authors: ^a remi.dreyfus@espci.fr - ^b jean.baudry@espci.fr - ^c has@deas.harvard.edu

Received: 4 February 2005
Revised: 17 June 2005
Published online: 21 September 2005

Abstract

An object consisting of three spheres, linked like the spokes on a wheel, can undergo a net rotational movement when the relative positions of the spheres proceed through a four-step cycle. This rotational motion is the analogue of the two-hinged swimmer originally proposed by Purcell (1977), which has served as a prototype for mechanical implementations of swimming. We also note that the rotational motion analysed here may be useful in the design of micromachines and has similarities to molecular-scale rotational motors that have been identified recently.