Crompton Parkinson provided three different systems, one on each of their two-car units. On the first, two faceplate controllers, driven by 50-volt motors, and an electro-pneumatic camshaft provided 57 notches between rest and full speed. The second system only had one faceplate controller, with the motors permanently connected in parallel, while the third used a motor-driven camshaft to control the switching of the resistances and the transition from series to parallel. The General Electric design used a motor-driven camshaft, which made three complete revolutions between rest and full speed, providing 56 notches. Transition from one notch to the next was based on time, but high motor current could delay the process. The Metropolitan Vickers system used an oil-driver power drum, which ran up to full speed in 45 notches. The resistance bank was reduced in size by using series-parallel switching of the resistances, which also meant that they heated up evenly. All four systems needed a 50-volt supply, and this was provided by a 5 kW motor generator set, which also powered the car lighting.