Why Do I Need a Cadence Sensor on My E-bike?

EU regulation requires an e-bike to only provide assistance when the crank is turning. The cadence sensor is typically added to satisfy this requirement. The algorithms in the motor controller may also depend on having the cadence value as an input along with other parameters like wheel speed, torque, braking, crank angle, inclination, etc.

Some sensors combine cadence and torque in one sensor, which simplifies the whole system and the installation. Some crank sensors even measure the crank angle for ultra-fast cadence detection.

You may also find e-bikes in the EU that are designed without a cadence sensor and rely purely on the torque signal to calculate when the crank is turning.

Some manufacturers interpret the EU machine directive in a strict way and even make sure the cadence detect signal does not involve any software at all in order to improve the safety of the e-bike.

This EU requirement is actually one of the difficult things in making an e-bike really responsive. The motor should start providing assistance instantly, but the time it takes to detect that the crank is turning may delay the start of the motor.

This is the reason we invented the term “angle-to-start” to have a way to characterize this essential parameter. How many degrees of angle are needed before the crank movement is safely detected and the motor can legally start?

With an angle sensor integrated with the torque sensor, the effective “angle-to-start” value can be down to 1-2 degrees with a delay down to about 1 ms (1/1000 seconds).  This will in practice completely remove the delay felt before the motor starts.