In the present paper, a rotational speed estimation method of a baseball is considered. In general, the gyro sensor is used for measurement of rotational speed. However, the gyro sensor in present condition can not measure for highspeed rotation. So, the signal processing procedure such as FFT or CWT (continuous-time wavelet transform) based on accelerometer signals are adopted instead of the gyro sensor measurement. First, the estimation procedure based on the three-axis accelerometer is described. Next, the estimation performances are verified in comparison with the estimation signals and measured signals by the gyro sensor by using accelerometer/gyro sensors which are built in a softball. By the result, it is verified that the estimated rotational speed by using CWT provides excellent performances in comparison with FFT and it is shown that it is able to simulate time variation of the rotational speed. Further, some estimation results for straight and curved ball by throwing experimental results by using the accelerometer built in a baseball are shown.
