Modelling of tennis racket impacts in 3D using elite players.

The modern era of tennis has seen large changes in racket design and playing style. As regulators of the game, the International Tennis Federation have assumed a role of constant investigation. Recently, impact models have been used to assess the characteristics of various rackets. Whilst existing models are powerful, they are limited in terms of impact position and racket and ball movement. Realistic shot characteristics of 13 elite level players at the 2006 Wimbledon Qualifying Tournament were obtained. Two high speed cameras running at 1,000 frames per second were used to record ball and racket movements within a fully calibrated 2x2x2 in control volume to an accuracy of ±2.5 mm. It was found that players tend to hit a point on the racket stringbed which generates little to no frame vibration. Forehand shots had an outbound ball spin of 800 - 2,200 rpm, ball velocities in the region of 25 - 40 ms'. The results from the player shot analysis were used in the design of a repeatable impact methodology. Nine hundred laboratory based racket/ball impacts were analysed in 3D. A custom racket mount simulated grip torque. The experimental outputs were interpreted using a multi-variate fitting technique. The experimental results were used in model validation. A predictive impact model was developed. When validated against the laboratory and player testing results, the model showed good correlation. The model was used to investigate the effects of shot weighting, movement and accuracy on post-impact ball behaviour. It was found that: Increasing swing action weighting increases the velocity of tip impacts. Increasing weight towards the edge of the racket reduces the penalty for hitting off the racket's longitudinal axis. A `chopping' action generates ball spin. The model developed in this study can be incorporated into existing shot prediction software used by the International Tennis Federation.