The Process
Tennis machines, also known as ball machines, are devices that allow you to practice tennis without a partner, as they receive balls "fed" from the other side of the court by a machine. Tennis machines work by projecting balls out of the machine either through a set of fast-spinning, counter-rotating wheels, or by using compressed air to "shoot" a ball out of a tube. Ball machines or their parts can oscillate to project balls to different areas of the court, and they are available in plug-in electric or battery-operated models.
Counter-Rotating Wheel Machines
Ball machines that use counter-rotating wheels project balls by compressing the soft tennis ball as it passes between the two larger wheels with enough force to shoot the ball across the court. Balls are usually stored in some form of bin or hopper, usually above the wheels, and move down into the projection area by gravity, as other balls leave the bin. If the counter-rotating wheels are placed horizontally (one above the other) and depending on the which of the two wheels is set to spin faster, these machines can produce topspin or backspin. Because the balls are repeatedly touched and deformed by the wheels, balls used in this type of ball machine wear out sooner than those used in pneumatic tube machines.
Pneumatic Tube Machines
Tennis machines that project balls using compressed air do so by placing the ball in a confined area so that it blocks the air moving out of the machine through the tubs. As air pressure builds (due to the blockage behind the ball), it reaches a level great enough to shoot the ball to the other side of the court. Ball machines that use compressed air provide a less consistent ball projection than those which use counter-rotating wheels, due to the fact that flaws in the tube, or how the ball lodges in the tube create different air pressures. Because the balls are acted upon only by compressed air, tennis balls used in pneumatic tube machines last longer. However, if an adapter is used to create spin, this friction on the ball will create more wear.
Oscillation
Ball machines can feed balls can feed balls to different areas of the court, including left and right and deep and short, if the machine has an oscillation feature. With pneumatic tube machines, the tube moves left or right or up or down, while the machine stays stationery. Machines using counter-rotating wheels either have the main body of the machine move while its supports stay stationary, or have the counter-rotating wheels move inside the machine. Balls can be directed to random or desired areas of the court using machines settings, which are inputted either on the machine or via a remote control.
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