The Notched Stick, an ancient vibrot example

Abstract

An intriguing simple toy, commonly known as the Notched Stick, is discussed as an example of a “vibrot”, a device designed and built to yield conversion of mechanical vibrations into a rotational motion. The toy, that can be briefly described as a propeller fixed on a stick by means of a nail and free to rotate around it, is investigated from both an experimental and a numerical point of view, under various conditions and settings, to investigate the basic working principles of the device. The conversion efficiency from vibration to rotational motion turns out to be very small, or even not detectable at all, whenever the propeller is tightly connected to the stick nail and perfectly axisymmetrical with respect to the nail axis; the small effects possibly observed can be ascribed to friction forces. In contrast, the device succeeds in converting vibrations into rotations when the propeller center of mass is not aligned with the nail axis, a condition occurring when either the nail-propeller coupling is not tight or the propeller is not completely axisymmetrical relative to the nail axis. The propeller rotation may be induced by a process of parametric resonance for purely vertical oscillations of the nail, by ordinary resonance if the nail only oscillates horizontally or, finally, by a combination of both processes when nail oscillations take place in an intermediate direction. Parametric resonance explains the onset of rotations also when the weight of the propeller is negligible. In contrast with what is commonly claimed in the literature, the possible elliptical motion of the nail, due to a composition of two harmonic motions of the same frequency imposed along orthogonal directions, seems unnecessary to determine the propeller rotation.

Surfactants and rotelles in active chiral fluids

“…By changing the legs' orientations, bristlebots can be manufactured to convert vibration into both translational and rotational motion. Bristlebots that rotate are called vibrots (29)(30)(31)(32). Vibrots must have a chiral leg configuration to rotate and can be designed for both senses of rotation (12).…”

Emergent Chirality and Current Generation

“…Chiral objects are an example of the aforementioned type. These objects convert linear momentum to angular momentum and thus twist and turn as they attempt to move under the influence of an external field [1][2][3][4][5][6][7][8][9][10][11][12][13][14]. A question of pertinent interest is then: Can an external field drive current in a system of achiral particles interacting only through steric hindrance, and that too not in the thermodynamic limit but for a system of a few particles?…”