Bipolar electric motor

The two coils were now separated and placed at the sides of the motor, with their iron core as a sideways figure-8 circuit and the armature in a central pole gap.

This circular layout also represented the end of the bipolar motor as an industrial power source.

It was possible to place a second set of field coils and pole pieces within the same size of casing, giving a four-pole arrangement.

This system would eventually predominate across both electric and diesel locomotives, but at this time it was difficult to produce a reliable high-power gearbox.

As the wheels and axle, and in this case the motor too, are unsprung by the suspension, any extra weight here would lead to poor riding qualities.

The armature was formed as part of the axle, but the much heavier field poles and coils were carried on the suspended frame of the locomotive.

They were eventually withdrawn owing to a general decline in US railroads in the late 1950s, the advent of cheap diesel power, and in particular to a rebuilding of the class that was poorly carried out and left the rebuilt locomotives with reliability problems.

They offer greater torque and speed than induction motors and so have many applications where their capital cost and light weight are more important than their electrical efficiency.

One well-known exception to this was the 'Taycol' range of motors, primarily aimed at larger model boats.

[3] These had their heyday in the 1950s and 1960s, becoming obsolete and uncompetitive in price as more powerful materials for permanent magnets, specifically ferrite, became available.

Taycol began with simple horseshoe magnet motors,[4] but their real speciality was with wound fields.

Their larger 'Marine' and 'Double Special' ranges used a dual-coil layout, with two vertical field coils mounted at the sides.