Extraordinary Tennis Ball Dropping Machine With this Tennis Ball Dropping Machine, you can practice playing tennis anytime, no need for someone to practice with you. You can use the equipment anywhere safe and spacious, since no power supply is needed. Features Lightweight No power supply needed No training venue limitations Enough ball capacity Adjustable height Specifications Frequency: 2 seconds Capacity: 33 balls Weight: 6.6lbs(without extra tracks) Height of dropping the ball: 51.2''-70.9'' Adjustable Height The height of the tennis ball dropping machine can be adjusted, so you can adjust the height of the rebound of the ball. The tennis machine is for different ages. No Power Supply Needed The tennis ball machine does not need any Power Supply to work. The operation of the device depends on the principle of gravity and inertia. Adjusting Block The ball dropping frequency can be adjusted from 2.3-2.8s by adjusting the adjusting block.