A PEDAL DYNAMOMETER FOR OFF-ROAD BICYCLING

This paper describes the design and accuracy evaluation of a dynamomet ric pedal, which measures the two pedal force components in the plane of the bicycle. To realize a design that could be used during actual o ff-road cycling, a popular clipless pedal available commercially was m odified so that both the form and the function of the original design were maintained To measure the toad components of interest, the pedal spindle was replaced with a spindle fixed to the pedal body and instru mented with eight strain gages connected into two Wheatstone bridge ci rcuits. The new spindle is supported by bearings in the crank arm. Sta tic calibration and a subsequent accuracy check revealed root mean squ are errors of less than 1 percent full scale (FS) when only the force components of interest were applied. Application of unmeasured load co mponents created an error less than 2 percent FS. The natural frequenc y with half the weight of a 75 kgf person standing on the pedal was gr eater than 135 Hz. These performance capabilities make the dynamometer suitable for measuring either pedaling loads due to the rider's muscu lar action or inertial loads due to surface-induced acceleration. To d emonstrate this suitability, sample pedal load data are presented both for steady-state ergometer cycling and coasting over a rough surface while standing.