With electric bicycles there's an option between having a throttle or not having a throttle. Traditionally a throttle-less electric bicycle was called "pedelec" or "pedal electric". The pedelec design lacks a throttle and instead controls the motor power in some other way.
The Charger bicycle was a pedelec design and there have been others over time. It seems though most electric bicycles have a throttle.
When my Charger bike still had the stock controller it was nice to just pedal & set the gear ratio without worrying over the throttle. On the other hand you had to pedal to get motor assist. While that enforces bicycling means exercise, it also precludes riding on motor assist alone
I noticed Currie has a pedelec design with a fancy sounding name ... http://www.izipusa.com/efacts.php ... TMM or "Torque Measurement System" is just a variation on pedelec designs.
They say: reads subtle changes in chain line force and drives the motor for pedal assist power. I suppose that's one way to do it. Another way is something like a magnetic sensor on the wheels to measure RPM.