Development of a low-cost measurement system to determine 3-dimensional pedal loads during in-situ cycling

As increasingly more bicycles are equipped with electrically powered pedal assistance, they can become the solution for the continuous congestion that threatens Europe. Pedal assistance decreases the effort, though cyclists often experience sores that occur at the low back, knees and bottom area. The risk of injuries is predominantly determined by the pedal technique, which is highly dependent of bicycle design, seat type and cycling posture. The optimal cycling technique and the relation to the bicycle characteristics needs to be discovered to create guidelines for bicycle construction and usage. This paper presents the design of a low-cost measurement system to analyse three-dimensional pedal loads in function of the pedal cycle by an instrumented pedal and an absolute encoder fixated on the crank. The pedal proposed is a combination of a unique steel sensor with twelve sensor regions, organized in four full Wheatstone bridges, installed on a standard pedal spindle. The pedals are calibrated with the Global Regression method acquiring a calibration matrix with a standard error percentage of full scale of maximum 0.5%. The instrumented pedal distinguishes itself from state-of-the-art techniques through (i) compatibility: it fits on every conventional bicycle, (ii) compactness: not influencing the cycling kinematics, (iii) broad applicability: it is applicable for in-situ measurements with extreme manoeuvres and (iv) accuracy: it delivers a relative high accuracy in relation to the production precision and production costs.