US Patent 8141438 Cassette-based power meter

A cassette-based power measuring apparatus includes a power sensing arrangement mounted within a cavity defined by a hollow bicycle cassette. The power sensing arrangement includes a torque sensing assembly including torque sensing elements configured to measure a user applied torque. The torque sensing elements are in communication with an electronics assembly configured to process the measured data and transmit it to a receiver. The torque sensing assembly may comprise a torque tube or a series of bending beams secured between a rear plate of the cassette and a freehub. The torque tube or bending beams may include strain gauges bonded thereto for measuring strain induced by application of forces in response to user-applied power.