This page tells you a fair bit about PAS options
PAS Options - Getting Started
Most ebikes these days offer some form of automated pedal control (PAS = Pedal Assist System), where the motor is powered in response to you pedaling the cranks and not just from a throttle on the handlebar. Here we summarize both the Cadence based and Torque based PAS sensors available for all...
ebikes.ca
The main thing with PAS is that almost no systems use PAS to control the amount of assist you get. They only turn the assist on, at full amount of the chosen assist level, if you are pedalling at all, and turn it off completley if you stop pedalling.
Most of them have different speeds for the assist levels, so if you pedal at all, the system will just do it's best to get you to the speed limit of the chosen assist level and hold you there, and if you stop pedalling it stops assisting at all. Even if you are trying to pedal slowly, but you're in an assist level for a faster speed, it's going to try ot get and hold you at the higher speed.
Some of them ahve the option for a "simulated torque" or power mode instead, so the assist levels equate to some amount of push instead of speed, but they still operate the same way--all or nothing.
Some of the open source firmwares OSFW you can flash / DIY into certain controller models/brands, and devices like the Cycle Analyst v3.x from ebikes.ca , allow you to use actual real cadence control of the system, so your pedalling speed actually varies the motor output directly.
Some systems (including the last ones above) also allow using torque sensors to tell how hard you're pushing on the pedals to vary the motor output. Some of them are more complex than others to setup, and most of them use some combination of torque and cadence to do this, so you may have to pedal at a certain rate to allow the torque sensor to work, etc.
if you have other questions let me know and I'll clarify whatever I can.
FWIW, you don't need PAS to get exercise while riding. You can use a throttle to control the motor along with your pedalling easily enough, with a bit of practice.
I did that for years on various builds before I built the SB Cruiser and eventually modified it for cadence-only PAS to fully control the 2WD dual motor setup on the back wheels of the trike, using a crank cadence sensor*** feeding into the Cycle Analyst v3, to vary the speed of the trike by varying my pedalling speed. The CAv3 just makes a throttle signal that tells "dumb" controllers (without assist levels, etc) what to do.
You can use "smart" controllers too, but the more smarts the controller has, the more complex the system can be to setup and work the way you want since you have interactions between the controller smarts and the CA smarts and the varying riding conditions and your input.....
***mine is integrated into the BB witha torque sensor but I'm not using hte torque sensor at present. The first link in this post shows a number of ways the sensors are made, so you can pick the one that works for you.
