 The ground floor houses the transformers for powering the wheel . When the wheel was flooded by vandals in April 2002 , this room was filled to within 8 cm ( 3 in ) of the 11 kV <unk> . On the first floor is a standby generator and switchgear should the mains supply to the wheel fail . The second floor houses a pair of hydraulic pumps that drive the hydraulic motors in the chamber above . Power is supplied directly to the axle with 10 hydraulic motors , which also double as brakes . Connected to each motor is a 100 : 1 gear system to reduce the rotation speed . 
