Abstract: A tennis ball throwing machine pneumatically expels tennis balls through a barrel having on one side of its inner wall a Velcro strip for spinning the ball. The barrel is rotated about its lengthwise axis so that the sense of the spin, topspin, backspin, or right or left hand spin, varies in dependence upon the angular disposition of the Velcro strip as of the moment the ball passes it. The output end of the barrel is bent at an angle to its lengthwise axis resulting in an orbital motion.

Abstract: Tennis balls are sequentially fed to an entranceway in the top of the plenum chamber of a pneumatic throwing machine by a flexible disk which rotates about a vertical axis. The balls roll by gravity down a chute onto the feed disk which has angularly spaced pocket holes. To prevent jamming of unpocketed balls between the top of the feed disk and the feed chute, the disk is sufficiently flexible as to be deflectable by an unpocketed ball and be discharged through an open escape path.

Abstract: Tennis balls are introduced via a removable ball pick-up magazine through a ball port in a wall of a pipe into a stream of air flowing through the pipe towards a barrel. Air flows freely through the barrel and through the ball port past a normally open flexible flap valve which permits a ball to pass, but which momentarily seals against the curved wall of the pipe in response to back pressure after a ball passes through the port and chokes the free flow of air through the barrel.