MPXM2102AS datasheet(127/670 Pages) MOTOROLA

127 / 670 page

AN1635

2–91

Motorola Sensor Device Data

www.motorola.com/semiconductors

The Baseball Pitch Speedometer works by exploiting the

fact that the final velocity of the target will be, according to

Eq. 1, linearly proportional to the initial velocity of the thrown

ball. Therefore, by measuring the acceleration response of the

system to various ball velocities, which can be measured by

independent means such as a radar gun, the system could be

calibrated and a linear model developed. To facilitate the char-

acterization and calibration of the system, a pitching machine

was used to ensure that the incident ball speed would be

repeatable. It also eliminated potential error caused by the

variability of location of impact on the target that would inevit-

ably result from several manual throws. Figure 3 shows a

linear regression plot of the response of the system as a func-

tion of incident velocity. As is indicated by the plot, just a simple

constant of proportionality could be used to correlate the mea-

sured acceleration response to the incident velocity of the ball,

with fairly accurate results.

Figure 3. Baseball Pitch Speedometer Characterization Data

10203040

5060

2000

4000

6000

8000

10000

12000

14000

BASEBALL SPEED AS RECORDED BY RADAR GUN (mph)

PREDICTED Y

IMPLEMENTATION — HARDWARE

The target mat of the Baseball Pitch Speedometer has an

area of approximately 9 ft2 (3 by 3). Even though the rubber

material used to construct the target is quite dense and

heavy, the transmission of an impact is very poor if the ball

strikes the target too far from the sensor. Therefore, to cover

such a relatively large area it is necessary to use at least

four devices; one centered in each quadrant of the square

target. In addition, a shock resistant plate about a quarter

inch thick is mounted behind the rubber mat. These features

help make the response of the system more uniform and

reduce errors that result from the variability of where the ball

strikes the target.

Freescale Semiconductor, Inc.

For More Information On This Product,

Go to: www.freescale.com

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