Variable radius drum mechanisms

This paper presents the concept of Variable Radius Drum Mechanisms (VRDMs). A drum, or spool, consists in a spindle with flanges, on which a cable is wound around. The cylindrical surface of an ordinary spool has a constant radius. In a Variable Radius Drum (VRD) the radius of the spool varies along its profile. Properties of such a devices are discussed, as well as kinematic analysis and synthesis. The main contribution of the work is the theory of the VRD synthesis problem rooted on a closed-form analytical solution. In order to highlight the benefits of VRDMs, two applications are presented and analyzed as examples. The first example consists in a mechanism which can support and guide a load along a horizontal linear path. The second example shows a solution to improve the locomotion of a legged robot.