| 摘要 |
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.
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