Falkirk Wheel, Scotland, United Kingdom

The slewing bearing at the machine-room end of the axle has an inner ring gear which is configured to act as a rotating annulus. The rotating annulus is driven by ten hydraulic motors which are assembled on a stationary bearing and motor assembly known as the planet carrier which in turn is also mounted onto a plinth similar to the one at the other end of the axle. The drive-shafts of the motors have pinion gears which act as stationary planetary gears in this train of gears and engage the rotating annulus ring gear. An electric motor drives a hydraulic pump which is connected to the hydraulic motors by means of hoses and drive the wheel at 1/8 revolution per minute.
• How the caissons are kept level
The caissons need to rotate at the same speed as the wheel but in the opposite direction to keep them level and to ensure that the load of boats and water does not tip out when the wheel turns.
Each end of each caisson is supported on small wheels which run on the inside face of the eight-metre-diameter holes at the ends of the arms, allowing the caissons to rotate. The rotation is controlled by means of a train of gears: an alternating pattern of three eight-metre-diameter ring gears and two smaller idler gears, all with external teeth. The central large gear acts as a stationary sun gear. It is fitted loosely over the axle at its machine-room end and fixed to a plinth to prevent it from rotating. The two, smaller, idler gears are fixed to each of the arms of the wheel at its machine-room end and act as planetary gears. When the motors rotate the wheel, the arms swing and the planetary gears engage the sun gear, which results in the planet gears rotating at a higher speed than the wheel but in the same direction. The planetary gears engage the large ring gears at the end of the caissons, driving them at the same speed as the wheel but in the opposite direction. This cancels the rotation due to the arms and keeps the caissons stable and perfectly level.