A wearable WIMU (Wireless Inertial Measurement Unit) (1) system for sports applications based on Tyndall's 25mm mote technology (2) has been developed to identify tennis performance determining factors, giving coaches & players improved feedback (3, 4). Multiple WIMUs transmit player motion data to a PC/laptop via a receiver unit. Internally the WIMUs consist of: an IMU layer with MEMS based sensors; a microcontroller/transceiver layer; and an interconnect layer with supplemental 70g accelerometers and a lithium-ion battery. Packaging consists of a robust ABS plastic case with internal padding, a power switch, battery charging port and status LED with Velcro-elastic straps that are used to attach the device to the player. This offers protection from impact, sweat, and movement of sensors which could cause degradation in device performance. In addition, an important requirement for this device is that it needs to be lightweight and comfortable to wear. Calibration ensures that misalignment of the accelerometer and magnetometer axes are accounted for, allowing more accurate measurements to be made. TennisSense is a joint project between the Science Foundation of Ireland (SFI) funded CLARITY Centre for Sensor Web Technologies and Tennis Ireland - the National Governing Body for the sport of tennis in Ireland - with the aim of developing a sensing platform to digitally capture physical, tactical and physiological data from tennis players in order to assist in their coaching and improve their performance. A major part of this joint project involves the capture and analysis of relevant kinematic motion data from the tennis players. This data will then be used to characterise a player's technique in order to provide accurate, quantitative feedback on player performance in near real time. To achieve this, devices that can capture the kinematics of an athlete during a tennis match are required. Tyndall was tasked with the creation of a wearable wireless inertial measurement gathering system suitable for use in the TennisSense project and possible future applications. The system would have to be able to accurately and simultaneously capture 6 Degree-of-Freedom (6-DoF) motion data at several locations on a tennis player over the full range of human motion. In addition the system would require a high sample rate, whilst remaining small, robust, lightweight, low power and not impeding or restricting the motion of the tennis players. Although the system is based on existing Tyndall 25mm mote technology, a significant amount of additional work was required to meet the specific requirements of the TennisSense application. This paper details the motivation for and the development of the above TennisSense system, outlining details on the device requirements, system architecture and design methodologies. A short discussion of the difficulties encountered in the course of developing and prototyping these devices and how these difficulties were overcome; further comments on future work are also presented.
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