Rowing performance monitoring system development

• Main Author: Williams, Thomas
• Language: en
• Published: University of Canterbury. Engineering 2012
• Online Access: http://hdl.handle.net/10092/6469

The aim of this work was to develop sensory devices and data acquisition system to facilitate investigations into the mechanics of the rowing system, comprising the rower(s), boat and oars. As such, the parameters to be measured were: boat and seat position, velocity and acceleration; oar force; foot force; oar angle and rower heart rate. An oar force sensor was designed that fitted into the cavity of a modified oarlock. This sensor design is cheap, yields sound results and its presence is almost not noticeable to the rower. A review of previously applied methods of oar force measurement, predating 1900, is included. Foot force is of interest to many different fields of research, thus there is a large amount of literature on the subject of foot force measurement. A comprehensive review of this literature is used to aid in the design of the required sensor. The combination of a non-simple dynamic loading (i.e. time varying spatially distributed normal and shear forces), with static foot position distinguishes the problem of measuring the force under the feet during rowing from most previously considered cases. A strain gauge-based force sensing plate was designed to measure both normal force distribution and unidirectional shear force under the feet. Sample results are presented from a study with international class New Zealand rowers on a rowing ergometer. The sensor, performs well under normal force loadings, but needs modification to measure shear accurately. Possible modifications are suggested. While only a single oar angle, known as the sweep angle, was required to be measured, a sensor combination capable of measuring the spatial orientation of the oar relative to the boat was conceived. A new method of relative orientation estimation, via approximation of the Rodrigues' vector, which allows relative weighting of sensory data, was derived. Unfortunately, calibration issues prevented the gathering of meaningful data in the time available. A full theoretical development, including a new calibration scheme, which should alleviate the encountered problems, is included. While the motion of the rower within the boat is an important consideration in the dynamics of the rowing system, few previous researchers have measured it. These previous methods are briefly described, before the sensor used in this study, the optical rotary encoder, is detailed. Differentiation of the encoder signal to obtain seat velocity and acceleration relative to the boat was achieved using a purpose designed simple Kalman filter. The kinematic parameters of the boat, i.e. position, velocity and acceleration were measured using a combination of accelerometer and submerged impeller. The information from these two sensors was combined using a variant of the Kalman filter used in the differentiation of the encoder signal. The combination of the seat and boat kinematics allows study of the motion of the system centre of mass. Supplying power to, and collecting data from the above sensory devices was a purpose built data acquisition system dubbed ORAC (On-the-water Rowing Acquisition Computer). ORAC was designed to transmit the collected information, in real-time, to a remote laptop computer via wireless LAN, but the system used proved to have insufficient range, and hence ORAC was used as a standalone computer.