Spin Shot Lite tennis ball machine

All quality tennis ball machines presently available on the market use wheels to throw the ball. Normally there are two wheels that turn in opposite direction (thus the label "counter rotating wheels") with a small space between them. The ball rolls down a chute and is squeezed by the counter rotating wheels which then eject it. The situation is similar to gravel being thrown from under a spinning tire, though in the case of the tire only one wheel is responsible for the "throwing".

2) Do machines with a tube that makes them look like a canon work the same way as machines that use counter rotating wheels for ejecting balls?

No, machines that look like a canon work by air pressure. Pressure is usually supplied to a drum by a vacuum cleaner motor. A ball is lodged at the throat of the tube and is retained by a collar that is slightly smaller in diameter than the ball. When pressure builds sufficiently to push the ball through the collar, the ball is ejected. Because these machines work on air pressure, they are called "pneumatic".

3) Is there any other way for a tennis ball machine to throw balls?

Yes, some machine use a "hammer" to strike the ball, and various spring loaded designs have also been developed. The performance of such machines is so limited that they are not discussed further here.

4) What's better: Counter rotating wheels or pneumatic pressure?

Today no machine costing more than about $700 works on the pneumatic principle. All better machines use counter rotating wheels. There are a number of reasons for this. Pneumatic machines are noisy and do not provide the high level of performance achieved by the better wheel driven machines. Pneumatic machines also require a lot of electrical current and cannot, therefore, be adapted to battery power. The only advantage of pneumatic machines used to be their low cost. Today they are a dying breed.

5) How does a machine put spin on the ball?

Wheel driven machines put spin on the ball by varying the relative speed of the upper and lower wheel. When the upper wheel turns faster than the lower wheel, the ball is ejected with topspin. When the lower wheel spins faster than the upper wheel, the ball is ejected with backspin. Of course, when both wheels turn at the same speed, the machine throws a flat ball. Pneumatic machines use friction in the canon tube or just outside the tube to impart spin. When the bottom of an ejected ball is rubbed as it exists the machine, the ball acquires topspin, and vice versa.

6) Can all machines put spin on the ball?

No, some wheel driven machines do not have spin capabilities. This is usually because the wheels are arranged in a horizontal plane rather than a vertical plane. By changing the relative speed of the wheels in a horizontal wheel machine, one could achieve side spin but no topspin or backspin. Because side spin is not an important element of tennis, manufacturers of horizontal wheel machines do not usually provide a spin adjustment.

7) What is an oscillator?

An oscillator is a mechanism that allows the machine to throw balls in different locations on the court. The most common type of oscillator, known as a random oscillator, causes the machine to sweep the court from side to side repeatedly much like an air fan sweeps a room. Balls...