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I am owner of a startup named CYKIQ in Pakistan. We just did our soft launch and got an amazing response from the customers. Out of many issues that we have solved one still remains and that is using bicycle for mid distance or intra-city transport. In order to achieve that I am developing a smart bicycle, will doing literature review I found our about pedelec sensor (while googling some sensor to find torque applied by the rider). Anyone who has used it and are willing to share the mechanism can you briefly explain the mechanism?

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    Some use torque sensors, others use cadence sensors. But if there are any experts in the design of such systems here, they're probably not going to share very much. – Chris H Aug 2 '16 at 14:59
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    From my understanding the torque sensors are used in higher end models as it can provide a smoother user experience by making it easier to more closely matching the user torque input, making it feel like you are simply stronger rather than the bike assisting your effort. Whether or not this effect is important depends on your use case and target customer. – Rider_X Sep 1 '16 at 21:06
  • @Rider_X that's interesting - and logical as a cadence sensor is cheap hardware. I've never ridden a high end e-bike and tend to use manual control when I do borrow an e-bike because I don't like the automation especially when going very slowly to time a gap. – Chris H Sep 2 '16 at 6:41
  • I think cadence sensor and speed sensor are interchangeable term because they are using the same mechanism : measure feedback over time. Just add tyres radius, you will get the speed. :-D – mootmoot Sep 8 '16 at 15:12
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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.

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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.

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