Armed to the teeth

Substantial speed reductions can be achieved in a robust mechanism that occupies minimal space by using planetary gears with two diameters in different sections, with different numbers of teeth. Design engineer Dr John Vranish, who works at NASA’s Goddard Space Flight Centre in Maryland, USA, and has his name on a whole host of patents, has developed the concept. Initially, it was aimed at space applications, but now the idea is being offered for general use and is likely to find major applications in robotics. Vranish calls this idea, a “phase-oriented gear system”, and a recent Nasa article has described how it might be employed in what it described as a “relatively simple speed reducing differential planetary transmission”. This consists of a sun gear, idler gear, three identical planet gears, a ground internal ring gear, and an output internal ring gear of slightly greater diameter and number of teeth. * An in-depth version of this article appears in the February 2008 issue of Eureka.