an instant tennis game simulating a real game of tennis is presented . a pneumatic tennis ball delivery machine replaces the normal opponent . the court is slightly crowned and has sloping gutters so that all balls are automatically , gravity - returned to the machine . solenoid controlled , motor - spun rollers permit simulation of various types of spins . ball trajectory from the machine is controlled by barrel angle , vertical and horizontal . the ball machine control system allows for repetition of one &# 34 ; shot condition &# 34 ; endlessly or a completely random variety of shots as directed by a programmed mini - computer or manually set &# 34 ; user controls ,&# 34 ; a program , or the equivalent .