An open-source, low-cost cycling power meter
Group Members
Liam Flavin, Christopher McGovern, Hao Kiat Phang, Matthew Walmsley, William Wheeler, Shinan Zhang
Supervisors
Professor David Simpson, Dr Thomas Blumensath
The OpenPower project aims to develop a low cost (£75) device capable of measuring power generated by a cyclist, known as a power meter. Devices already available on the market come at a significant cost, limiting user uptake.

The proposed product will be manufacturable by a hobbyist, making the most of low cost ’off the shelf’ components whilst still being capable ofproviding a similar accuracy. The product developed is a spider-based power meter, water-jet cut from aluminium and populated with 10 strain gauges. These feed into a Wheatstone Bridge, associating an applied force with a calibrated voltage before being communicated from an Arduino Nano processor via BLE to an Android phone. Electronic components are contained in a 3D-printed housing. Whilst testing was limited as a result of the COVID-19 pandemic, the initial goal of the project was met.

Static testing proved a proportionality between loads being applied to the spider and a change in measured voltage, functional for both loading and unloading cases and able to be communicated to the phone over BLE. Future development would include further testing in real world conditions by examining recorded power under variable applied power and cadence.
Assembled final OpenPower iteration, pre-testing

 

: Assembled final OpenPower iteration, fitted to bicycle testbed
Exploded diagram of an early modular spider design, consisting of two 4mm aluminium plates and five 1mm washers and showing fitment to a standard crank and chainring. Electronics housing omitted for clarity

 

Front view render of final OpenPower spider design

 

Rear view render of final OpenPower spider design.

 

Rear view render of final OpenPower spider design installed, illustrating crank-spider and spider-chainring interfaces