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Motorola Sensor Device Data
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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
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BASEBALL SPEED AS RECORDED BY RADAR GUN (mph)
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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.
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