Mechanical Engineering, "Technology Focus" 2002

Power Transmission and Motion Control

No More Rag Arm

The search for a better pitch led ProBatter Sports engineers to the sales department of Cranston, R.I.-based Mearthane Products Corp. ProBatter of Milford, Conn., wanted to add durability to its batting cages. With a video pitcher throwing in consort with a curveball pitching machine, the cage already offered plenty of realism.

According to ProBatter's president, Greg Battersby, many pitching machines use two counter-rotating wheels to throw a ball. His company's machine adds a third wheel, by which the machine can throw fast balls and every pitch tossed in the Major Leagues, save the knuckleball. To do so, the machine varies individual wheel speed from 1,500 to 2,500 rpm.

Just when star pitcher Vid Eo is about to release the ball,
a throwing machine backing him up tosses one out a screen opening.

Rubber-coated wheels gripped each ball in the original machines. But they wore prematurely—in as few as 30,000 cycles—because of the demands placed on the rubber as it accelerated the balls to speeds near 100 mph. Once the cycle of wear began, wild pitches increased, until replacement wheels had to be brought in to relieve the pitchers 10,000 throws later.

Downtime to replace the wheels bothered commercial users, who expected the equipment to throw 10 pitches a minute 16 hours a day.

In seeking a better material, Mear-thane engineers cast several urethane prototypes before selecting one in the 40-45 Shore A durometer range. The material needed to grip and wear well on both the urethane covering amusement-park balls and the stitched-cowhide outers the pros handle.

The new wheels throw quite a few innings before needing relief.

This section was prepared by Associate Editor Paul Sharke.
© 2002 by The American Society of Mechanical Engineers