The vast majority of eBikes have pedal assistance. Pedal assistance is the motor providing extra power while you pedal. Most bikes will have 3 or 4 levels of assistance that range from minor assistance for flat ground to much more powerful assistance to get you up a hill. Pedal assistance on a bike works in one of two ways.
The basic cadence sensor uses a magnet on the crank, it turns the motor ON when you start pedaling and turns it OFF when you stop pedaling. It works more or less like a switch. Using the cadence sensor, you have to control the boost level and speed by adjusting the assist mode manually up and down. Most basic e-bikes offer a cadence pedal sensor. The advantage of this sensor is that it’s an inexpensive way to get some sort of pedal-assist onto the bike, but the disadvantage is that the pedal assistance can feel jerky, laggy, and counterintuitive. Also if you want to pedal faster than the motor is spinning, the motor will actively work against your efforts.
Torque Sensors (Advanced)
The torque sensor is a totally different technology that uses a precision strain gauge. It measures your actual force on the pedal, sampling at 1,000 times per second over the entire pedal stroke. A torque sensor measures how hard the rider is pedaling to determine how much electric power to push to the bike. The harder you pedal, the more power it gives to the motor. If you pedal lighter, less power goes to the motor. It makes this adjustment in real-time so it is technically amplifying your every input and makes the rider feel BIONIC! Many higher-end e-bikes use torque sensors and in some countries, cadence-only sensors are not allowed to be sold. The disadvantage is the cost is significantly higher to implement this technology as the precision component is relatively more expensive.