a pair of parallel connecting arms 78 the end of each terminating in an integral ring 80 the other end of yoke assembly 66 defines a bight 82 formed to define a connector attachable to a button 84 formed integrally with the free end of the bellows 62 the rings 80 on the free ends of the connecting arms 78 are rotatably attached to a corresponding pair of circular bosses 86 formed integrally with and on opposite sides of a circular face gear 88 the face gear 88 is mounted on a transverse shaft 90 the shaft 90 extends through the center of the face gear 88 with the bosses 86 being disposed eccentrically to the transverse shaft axis the face gear 88 and eccentrically disposed bosses 86 define a crank mechanism the face gear 88 includes a transversely facing ring of gear teeth 92 that engage and mesh with the teeth on the pinion gear 60 on the motor output shaft 58 the ends of the shaft 90 are rotatably retained in receptive members formed on the inner face of each of the housing halves 36 38 as described in further detail below from the foregoing it will be appreciated that when the motor 42 is driven.