# Inside an Escalator

An anatomy\-style cutaway of an escalator: the loop of steps, wheels and tracks, step chain, drive machine, handrail and combs that riders never see

By Numa

Topic: Machines

[Open the interactive Jig](https://ask.jig.com/j/Rb09kjb4JdFJ)

## Guide

### 1. Inside an Escalator

Escalators carry millions of people between floors every day\. We have opened this one up and taken away the side nearest you, so you can see the hidden machine riders never notice\. Drag anywhere to turn it around\.

A typical escalator moves about half a metre every second\.

### 2. A loop of steps

The steps are not a staircase that grows out of the floor\. They form one closed loop, like a necklace of 52 steps\. After you step off at the top, each step flips over and rides back down underneath, upside down\.

At any moment, almost half of the steps are hidden on the trip back down\.

### 3. Two wheels, two tracks

Each step rolls on two pairs of small wheels\. The front wheels, shown in teal, run on one track\. The back wheels, called trailer wheels and shown in violet, run on a second track set at a different height, which keeps every step level on the slope\.

Near each end the tracks bring the steps into line, so they flatten into a smooth floor\.

### 4. The step chain

Every step is fixed to two long chains, one on each side\. At the top, big toothed wheels called sprockets pull the chains, so the whole loop moves together\. Going round the sprocket, each step tips over and heads back down\.

Each chain link is about 133 millimetres long\. Three links make the 40 centimetre space between two steps\.

### 5. The drive machine

Under the top landing sits the heart of the escalator: an electric motor\. A gearbox turns its fast spin into a slow, strong turn, and a drive chain carries it to the main shaft\. A brake on the motor can hold everything still\.

The brake is held open by electricity, so it closes by itself if the power goes off\.

### 6. The handrail

The handrail is a long rubber loop too\. It glides along the top of the balustrade, the glass side wall, then returns inside the frame\. A drive wheel, turned by a chain from the main shaft, pushes it at the same speed as the steps\.

Under its rubber skin, the handrail has layers of fabric and thin steel cables that stop it stretching\.

### 7. Turning round at the bottom

At the bottom, the chains wrap round a second pair of sprockets\. Their shaft sits in a sliding carriage, and springs push it toward the end of the frame\. That keeps the chains snug as they wear and stretch over the years\.

If a chain ever stretches too far or breaks, a safety switch stops the escalator\.

### 8. Combs and safety

At each end, the steps slide under a comb plate\. Its teeth fit into the grooves of the steps, so shoes and small objects are lifted off rather than pulled in\. If something jams, a switch stops the escalator, and so does the red stop button\.

The yellow lines mark the edges of each step, showing you where to stand\.

### 9. Follow one step

Now follow the highlighted step on its whole journey: up the slope, under the top comb, upside down along the return and back to the start\. Press the button to speed the machine up and ride the full loop with it\.

At normal speed, one trip round this loop takes about 40 seconds\.