Instrumented bicycle pedals for dynamic measurement of propulsive cycling loads

Abstract

A system was developed for measuring and analyzing the forces placed on a bicycle pedal during operation of a stationary ergometer. Forces are measured in the plane parallel to the ergometer in directions normal and tangential to the surface of the pedals, encompassing the plane of propulsive forces. The pedals are designed to be structurally and functionally equivalent to standard clipless pedals. The stock pedal spindle and bearing assembly was replaced with a new spindle that was instrumented with two Wheatstone bridges of foil strain gauges. The bearings were relocated to the crank-arm/pedal-spindle interface. The original pedal body was then pinned to the new spindle. Additionally, the pedals were instrumented with optical encoders to measure the pedal angle relative to the crank arm. An optical encoder was also mounted near the bottom bracket to measure crank-arm angle. Signals were transmitted via a cable tethered to the cyclist’s leg from the pedals to an instrumented chassis, where the strain gauge signals were conditioned and the digital optical encoder signals converted to analogue signals. From the instrumented chassis, seven signals are ready for standard analogue data collection. Data collected from this new system has proved to be both comparable with previously published literature and accurate when compared with expected power output values.