INSTRUMENTATION AND PADDLE RACKETS

  • Noé Gomes Borges
  • José Carlos Pio da Fonseca
  • Helio Roesler
Keywords: paddle rackets, instrumentation, coefficient of restitution, vibrations

Abstract

Tennis rackets have long been studied, but just recently attention has been focused on paddle rackets. Knowledge of racket characteristics and properties will contribute to its improvement, better athletic performance and, most important, injury prevention. Compromise between a high coefficient of restitution and vibration absorption should be achieved. Paddle rackets are suitable to accept surface bonded sensors, thus making electronic instrumentation an efficient way to investigate mechanical problems such as impacts, vibrations, strains, and so on. The aim of this paper is the description of an instrumentation setup designed to investigate some important mechanical characteristics upon paddle rackets. Coefficient of restitution for a constrained racket setup was determined using a pneumatic ball cannon and a lab-designed laser and photo diode reflective window. The cannon shot was adjusted in order to provide ball speeds within expected competition values. The laser window consisted of a wooden frame with a pair of parallel mirror strips facing each other, reflecting a zigzag laser beam provided by a low power pointing device. The zigzag beam detected light interruptions during the ball passing through, anywhere inside the window. Processed and analyzed, the signal informed about the time interval between pre and post ball impact on the racket. Speeds could thus be calculated and used with the appropriate formulae to obtain the coefficients of restitution. Piezoelectric transducers were bonded to the racket surface and handle. Held by a wire, in a vertical position, rackets were hit by a magnetically driven hammer, at different heights on the longitudinal axis of symmetry, allowing us to locate vibration nodes. Two of them were detected; the first at about 110 mm from the free racket end and the second on the handle. These nodes are points which once impacted excite the lowest amplitude vibrations in the structure. Associated with suitable theory, our results are contributing to paddle racket improvements. New rackets have been designed taking those results into account. A hollow racket is an example; Laboratory tests have shown that the coefficient of restitution is higher and vibrations lower than those of compact rackets, as a consequence better performance and a reduction in injury are expected.