11 Jan '15, 12pm

Grinding a Bicycle Crank for Power Analysis

The usual way of measuring torque is by measuring how much the axle twists. You have two optical or capacitive stripe patterns going around the axle at one end near the cog, and another at the other end near the pedal. The harder you pedal the more the phase of these two repeating patterns shift relative to one another because the axle twists slightly. This is how you don’t need to fix electronics to a spinning piece of metal. A couple discs with stripes and optical gates will do, or even a single disc if you know how fast the crank is turning at all times. Torque measurement is a requirement in e-bikes in the EU because they can’t turn on unless the user is pedaling, so a common way is to measure torque from the crank and add power to the back wheel in proportion. These things are sold on the market: https://d10kui8makj4zw.cloudfront.net/wp-content/uploads/2012/10/npd-5.j...

Full article: http://hackaday.com/2015/01/11/grinding-a-bicycle-crank-f...

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