The electric motor requires a 12-14 volts supply.
The loco picks up current from the outside track (right or left
rail) by the side collector shoes (25). Note that these side shoes may be
fitted either to the near side or to the off side of the loco.
In the 4-4-0 loco, current is picked up from one of the outer rails
by collector shoes fitted to the tender. Electrical connection from tender to 4-4-0 loco
is made through the tender towing pin, although a few 4-4-0's have a wire connection
between loco and tender.
From the side shoes (which are insulated from the chassis) current
passes to the coil of the field magnet (40) making a magnetic field in
which the armature (48) revolves.
Current then passes via the middle contact spring (19)
to the contact shaft (45) and from there to the outer contact
springs (20). The current flows through the carbon brushes to
the commutator of the armature.
The rotary motion of the armature turns the pinion gear
wheel on the armature shaft (just seen behind the nearest pole
winding (48) which drives the reduction gear wheels.
The smaller of these engages with teeth on the driving
wheels (4) and makes them rotate, driving the Ioco along the track.
Four successive quarter revolutions of the contact shaft (45) give us
1. Forward speed.
3. Reverse speed.
Because of the inter-action between the springs (19 and 20) and the
contacts of the contact shaft (45), the direction of the current through the armature (48)
is changed so that in positions I and 3 the motor runs in the clockwise or anti-clockwise
direction respectively. In positions 2 and 4, however, the springs (20) touch insulated
portions of the shaft, the current is interrupted and the motor stops.
dismantle the loco proceed as follows, having first spread out a sheet of paper to save
small screws, etc., from falling on to the floor.
After long use the loco may need an overhaul.