It takes just 22.5 kilowatts (kW) to power the electric motors, which consume just 1.5 kilowatt-hours (kWh) of energy in four minutes, roughly the same as boiling eight kettles of water.The wheel, which has an overall diameter of 35 metres, consists of two opposing arms which extend 15 metres beyond the central axle, and which take the shape of a Celtic-inspired, double-headed axe. Two sets of these axe-shaped arms are attached about 25 metres apart to a 3.5 metre diameter axle. Two diametrically opposed water-filled caissons, each with a capacity of 80,000 gallons (302 tons), are fitted between the ends of the arms.These caissons always weigh the same whether or not they are carrying their combined capacity of 600 tonnes of floating canal barges as, according to Archimedes' principle, floating objects displace their own weight in water, so when the boat enters, the amount of water that leaves the caisson is exactly the same as the weight of the boat. This keeps the wheel balanced and so, despite its enormous mass, it rotates through 180° in less than four minutes while using very little power.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 drop out when the wheel turns.The end of each of the caissons is supported on small wheels which run on the inside face of the eight metre diameter holes at the end of the arms, enabling the caissons to rotate freely.The rotation is achieved by means of a train of gears comprising three eight metre diameter ring gears with external teeth and another two small jockey gears. One of the large gears acts as a stationary sun gear and is fitted loosely over the axle at the machine-room end of the axle and fixed to a plinth to prevent it from rotating. The two small jockey gears, the outer rings of bearings, are fixed to each of the arms of the wheel at the machine-room end of the wheel and act as planet gears. When the motors rotate the wheel the arms swing and planet gears engage the sun gear which results in the planet gears rotating at a higher speed than the wheel but in the same direction as the wheel. The planet gears engage the large ring gears at the end of the caissons causing them to rotate at the same speed as the wheel but in an opposite direction. This keeps the caissons stable and perfectly level.