These notes include types of motor that are no longer commercially available, having been superseded by more modern designs with superior characteristics. However, model railway locomotives often have very long lives, and these notes may assist in repair or refurbishment, or replacement with a more modern motor if the original motor has failed.

Early types of motor had the armature set across the frames and drove the axles through spur gears. As more powerful motors were demanded the armature diameter was increased but its length was limited by the dimension between the frames. Turning the armature to run parallel to the frames avoided this limitation and the resulting increase in motor power led to this becoming the normal arrangement.

Figure 1 illustrates a Bassett-Lowke ‘Permag’ motor of this type. Similar motors were produced by Bonds, Leeds Model Co and Milbro. They were usually supplied as a unit complete with gears and locomotive driving wheels.


Figure 1. Bassett_Lowke ‘Permag’ motor.

Motors with transverse armatures continued to be manufactured, notably by Hornby, and their power was often increased by using wound field magnets in conjunction with reversing switches mounted on the locomotive. These are now generally found only in models of interest to collectors. The Lima motor has a transverse armature and a modern very powerful permanent magnet, a combination which gives adequate power for multiple units and small locomotives.

The motor illustrated in Figure 1 was fitted with a single piece permanent magnet but the development of improved magnet steels led to the use of block magnets with separate pole pieces (Figure 2). The improved magnetic strength meant that a lower current was required to produce a given torque.


Figure 2. Romford motor.

After 1945 both solid magnets made from the improved magnet steels and block magnets with separate pole pieces were used but due to their better magnetic properties coupled with ease of manufacture the latter soon became the general practice, although they have now been largely superseded by magnets moulded from still better materials. The Bonds motor illustrated in Figure 3 is a post-war design using a block magnet, it was supplied with an integral gearbox which greatly simplified installation.


Figure 3. Bond’s motor.

The development of many devices such as tape recorders and computer printers has enormously increased the demand for small electric motors, many of which are suitable for gauge O locomotives. At the same time further development of permanent magnets resulted in the production of alloys which, although unmachinable by conventional methods, could be accurately moulded to form pole pieces for small motors.

Modern motors typically feature:

• An armature with an increased number of poles giving a smoother torque, particularly at low speed,
• Self aligning oil impregnated bearings give low friction,
• High strength magnet results in a substantially lower current being required to produce a given torque and this in turn reduces the overall size of the motor, and the current rating required for the power unit and controller.

This article was compiled by the Technical Committee for the Gauge O Guild Manual. It was adapted for the GOGWiki by Nick Baines.