Power meters have been gaining in popularity among cyclists as an important tool in providing training feedback. One of the major challenges in producing a transducer for cycling applications is temperature excursions it is likely to experience during a ride. Due to these temperature variations, Dyno Velo needed to develop a sensor that would be less sensitive to temperature, or set the sensor output to be much more sensitive to torque than to thermal effects.
To measure the power generated by a cyclist, Dyno Velo developed a unique transducer to measure the crank spindle’s torque from the left leg during cycling, so as to convert the torsion-based output to units of power exerted during the pedaling process. One of the challenges in the transducer design was that bending loads could exceed the shear load (torque) in the spindle. Thus, a custom torsion gage having a high manufacturing tolerance was needed to solve the problem.
Working with Micro-Measurements, a custom gage was built cost-effectively, with the tight tolerances required and with low power consumption (a requirement dictated by battery power). Also of great importance was the desire to reduce, if not completely eliminate, the effects of day-to-day temperature changes on the power meter’s accuracy. Through the expertise of Micro-Measurements engineers and their white papers on strain gage technology, Dyno Velo engineers were able to isolate and decouple metallurgical and mechanical issues from thermal issues, and to identify other variables compounding the temperature effects.
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