Abstract: A large dish member for use as a solar collector, radar antenna or the like is mounted on a tripod structure on a first set of bearings which permit rotation about a polar or azimuth axis, and a second set of bearings which permit rotation about an elevation axis. Drive about the elevation axis is achieved by means of a linear actuator with elevation position being sensed by means of a position transducer such as a selsyn. Drive about the polar or azimuth axis is achieved by means of two motors, one for slow drive, the other for fast drive, both of these motors being coupled through a timing belt drive and worm gear reducer to a drive sprocket. The drive sprocket engages a chain which is welded to the rim of an arcuate spoked drive member in the form of a wheel segment, which is fixedly attached to the dish member and mounted for rotation on the support structure. A position selsyn is provided to sense azimuthal or polar position.