# How Electric Bicycles Work

See how a pedal\-assist e\-bike senses your pedalling and adds motor power from its battery

By merry\-heron\-7e9d39eb

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/tHNpjA5k9E23)

## Transcript

### 1. How Electric Bicycles Work

An e\-bike is a bicycle that helps you pedal\. A small motor adds power only while you push the pedals\. Follow how it senses your effort and where the power comes from\.

### 2. Four Parts Make It Electric

A battery stores the energy\. The drive unit holds the motor\. The display sets how much help you get, and a speed sensor at the back wheel tells the bike how fast it goes\.

### 3. Inside the Drive Unit

This simplified view shows an electric motor driving a large gear on the pedal axle\. The gear slows the fast motor down and makes it stronger\. A sensor measures how hard you pedal, and a controller makes the decisions\.

The motor parts are simplified; real drive units differ by brand\.

### 4. Sensors Read Your Pedalling

The torque sensor feels how hard you press, and the speed sensor counts wheel turns\. The controller reads them many times a second\. Push harder and watch the motor answer\.

### 5. The Battery Stores the Energy

A lithium\-ion pack on the down tube supplies about 36 volts\. A typical pack holds about 500 watt\-hours\. It locks into a rail and slides out for charging indoors\.

### 6. You Choose How Much Help

The controller turns battery power into motor power\. In Eco the motor adds a little more than half of your effort; in Turbo it adds more than three times as much\. Pick a level and compare the bars\.

Eco 60%, Tour 140%, Turbo 340%: typical Bosch settings\.

### 7. Help Fades at 25 km/h

In Europe the motor may only help up to 25 km/h\. Near that speed the help fades away, and above it you ride on your own power\. Slide the speed and watch the motor bar\.

US Class 3 e\-bikes may help up to 28 mph \(45 km/h\)\.

### 8. Hub Motors Work Differently

Some e\-bikes put the motor in the back wheel hub instead\. It turns the wheel directly and does not use the bike gears\. Switch between the two designs\.

### 9. Charge and Ride

Plug the battery into its charger at home\. One charge usually lasts 40 to 120 km, depending on the assist level, hills and rider\. You still pedal on every ride, just with a helping hand\.