Pedal Sensing and Torque Sensing, which is better and why...
A common usage in the bicycle manufacturing industry is that a cadence sensor determines if you are pedaling and direction (forward or backward) while a torque sensor in addition measures how hard you are pedaling. Both systems require the use of a computer to detect the pedaling and determine the signaling sent to the controller that in turn powers the motor.
Often stated, toques sensing is better, is an opinion about the rider’s response to a type of ride quality. The feel of torque sensing is a combination of responsiveness and subtle increase in power as you increase the force of pedaling. This produces a unique sensation of increased power and thus strength to the rider’s effort. Most common implementation of this on a retrofit bike is a bottom bracket loaded with a torque sensing crankset, available in square taper and ISIS as of this writing.
Cadence and pedal detection can be done in a number of ways. On the Calfee Electrofit the sensing is done with a magnet ring attached to the innermost chainring and a below the BB sensor that reads the magnet ring. The system detects direction of the pedaling as well. This information is used to power the motor and is very responsive and smooth when engaging.
The answer to which is better is subjective and is perhaps best understood as a restriction of application as torque sensing in a retrofit restricts the use of cranks to a set described here. Road bike enthusiasts wishing to retrofit their existing platform will immediately realize the issue, there isn’t much choice.
More information on power leveling is on the way in the next Electrofit blog entry.