While doing a literature review I found out about pedelec sensors (while googling some sensor to find torque applied by the rider). Is anyone who has used it willing to share the mechanism and can you briefly explain the mechanism?
From my experience working with electric bikes, most of what I saw were sensors that were mounted on the crank which measure your biking cadence. A sensor would be fixed around the bottom bracket, and then a ring of magnets would spin with the crank, 'tripping' the sensor every time a magnet passed.
They're called hall effect sensors and should be easy to integrate into your design as buying just the PAS sensor is relatively inexpensive.
You can find a Wikipedia page that covers Pedelec sensors here.
Compare to a torque wrench, Bicycle torque sensing are quite tricky. Checkout wikipedia torque sensor
Torque sensor need good material QC, electrical measurement component and good sensor, AKA : expensive. And it is difficult to make a DIY kit to install it properly. But the benefit is a direct feed to your motor, increase output when torque feedback are high = smooth pedal assist, save power when low torque sensed. Pedelec that use torque sensor will also use speed sensor to cut off the motor when it reach the "legal limit".
OTH, speed/cadence sensing is much easier, you just need a simple feed : use a magnet or reflector to measure the gap and timing. So it works reverse : power always on, power cut off when the speed goes above the limit. "Power assistant output level" is pretty important here to save the energy.