Ball throwing device for tennis balls

A ball throwing device capable of automatically accommodating and throwing balls of different diameters, said device comprising:

• a carrier member supporting a first roller for rotation about a first axis;
• a rocking lever pivoted to said carrier member about a pivot axis parallel to said first axis and supporting a second roller for rotation about a second axis parallel to said first axis;
• a motor mounted to directly drive only one said roller;
• a spring mounted to urge said rocking lever to pivot about said pivot axis in a first direction to urge said second roller toward and into friction contact with said first roller such that drive of said one roller is transferred to the other said roller due to said friction contact therebetween;
• a ball feeder to feed a ball to a region between said rollers such that rotation of said rollers throws the ball;
• and
• the passage of the ball between said rollers urging said second roller away from said first roller and pivoting said rocking lever against the force of said spring in a second direction opposite to said first direction, during which said drive of said one roller is transferred to said other roller by the ball therebetween.