Escalator

A staircase on a chain. Two wheel tracks fold the steps into stairs on the slope and flatten them into a floor at each end.

• Each step rolls on two wheel pairs: chain wheels in front, trailing wheels behind, each on its own track.
• The trailing track is the chain track shifted back and down. So the tread stays level everywhere. On the slope the shift makes stairs; on the flat it makes a floor.
• Past the comb, the steps dive under the floor, flip upside down, and ride back underneath.
• One motor drives it all: motor → gearbox → drive chain → main shaft. The same shaft turns the handrail, so hand and feet move together.
• The brake is fail-safe: springs press it shut, and only power holds it open. Lose power and it stops.