47, a). It was
found necessary to push the armature along the spindle close to the
commutator piece, C, and to shorten the spindle at the armature end and
turn it down to the size of the original bearing, in order to bring the
motor within the space between the wheels.
The place of the small pulley was taken by an 8-toothed pinion wheel,
engaging with a pinion soldered to the near driving wheel, the diameter of
which it exceeded by about 3/16 inch. The pair, originally parts of an old
clock purchased for a few pence, gave a gearing-down of about 9 times.
The position of the driven wheels relatively to the armature must be found
experimentally. There is plenty of scope for adjustment, as the wheels can
be shifted in either direction longitudinally, while the distance between
wheel and armature centres may be further modified in the length of the
bearings, BE. These last are pieces of brass strip turned up at the ends,
and bored for axles, and screwed to the under side of the base. To prevent
the axles sliding sideways and the wheels rubbing the frame, solder small
collars to them in contact with the inner side of the bearings.
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