|Description||The VeloDAQ power measurement pedal is a self-contained data acquisition system used to analyze
a cyclist’s pedal stroke and wirelessly transmit that information to the rider’s smartphone. The
VeloDAQ is comparable to other pedal based power measurement devices on the market with the
exception of two profound characteristics. First, the VeloDAQ transmits its data via Bluetooth to
the user’s smart phone; this reduces cost and avoids proprietary communication protocols by using a
device a cyclist is likely to already own. Second, the VeloDAQ pedal is the only product that
provides a display of force as a function of crank angle, a new but important metric to analyze a
cyclist’s pedal stroke (as opposed to only power measurements). These two differences allow the
VeloDAQ to be less expensive, and therefore more accessible, while still providing greater
functionality than similar products already on the market.
The design presented is built around already existing pedal technology in order to minimize the cost
of production while maintaining a traditional clipless pedal form factor. To measure applied pedaling
force, the VeloDAQ uses strain gauges in half Wheatstone bridge configurations mounted along the
circumference of the pedal spindle. Within the pedal, angular position and velocity are measured
using a Hall effect sensor at a greatly reduced cost when compared to other technologies such as
encoders and accelerometers. The output of the Wheatstone bridges and the Hall effect sensor are
then sent to an on board microprocessor and transmitted via Bluetooth to the users smartphone or
computer which displays the final data for the user. All added components are housed inside a
custom designed enclosure that closely follows the style of the original pedal.
Testing of the design shows that the pedal is capable of measuring applied forces within ±0.79
pounds and angle within ±2.3 degrees during steady cadence. Due to a failure in one of the strain
gauge circuits during final testing, bridge 2 showed an error of ±16 pounds. While significant, this
error is not caused by a failure in the methodology, rather implementation and circuitry failures.
Final road tests of the pedal were not performed due to irreparable damage to the prototype system.
The VeloDAQ sensors performance, when coupled with high data transmission rates and low
power consumption standards for Bluetooth (300Kbs and 30mW respectively), creates a system that
can provide a cyclist with many hours of high quality data collection. When this information is
applied to a training regimen, it can be used to improve the efficiency and power generation of a
cyclist over more traditional systems that only provide basic power production and cadence data to