| Abstract |
In cycling, force applied to the pedal is conventionally measured using strain gauges or piezoelectric force transducers within the pedal body or at the crank. This thesis takes a different approach to determine pedal force based on motion capturing.
Pedal force is calculated as the sum of forces needed to overcome the resistance of the ergometer brake and the moment of inertia of the ergometer's flywheel. The former is obtained from cadence and power measurements of the ergometer, the latter by means of flywheel inertia and angular acceleration of the crank.
The crank angle was determined by tracking the pedal movement using motion capturing. Then the second derivative of the crank angle gave its angular acceleration. As noise inherent in measurement data causes serious problems when computing derivatives, the data was smoothed beforehand. Three smoothing techniques were applied: a Butterworth filter, a Kalman smoother, and singular spectrum analysis. The angular acceleration obtained by the three methods was similar.
The analysis of the pedal motion data revealed that systematic errors and strong measurement noise prevent sufficiently accurate estimates of the angular acceleration of the crank. Therefore, the resulting pedal force estimates differ considerably from the force obtained by a pedal force measurement device (Powertec System). |