Determination of spin rate and axes with an instrumented cricket ball

Abstract

An instrumented cricket ball was developed with three single-axis rate gyros with a measurement range of ±350 rad/s (55.56 rps). The gyros, a miniature data logger and a battery were incorporated into a CNC machined ball with a seam. The data were collected at 500Hz and downloaded via the logger's USB port. The gyros were calibrated before inserting them into the ball. The output data provided the spin rates about all 3 axes, from which the resultant spin rate and the position of the spin axis were calculated. The axis was displayed as the axis point, the intersection of the axis with the surface of the ball, as well as 3D visualization of the ball and the spin axis surface (movement of the axis with time). The initial spin rate of the ball thrown by two subjects ranged between 10.5 rps and 18.4 rps. The spin decay ranged between 0.002 and 0.584 rev/s2 and was always linear. The spin axis, initially perpendicular to the plane of the seam can show considerable deviation towards the seam. The smart cricket ball is an invaluable tool for training and characterization of bowling deliveries.