IBM Selectric I/O Manual Of Instruction page 9

Drive
An eight-toothed motor pulley provides positive drive for the
operation of the machine. A positive-drive belt transfers the
rotation of the motor pulley to the cycle clutch pulley with a
speed reduction of 3-5/8 to 1 .
The shaded pole motor has less starting torque than the cape-
ci tor-start motor • To insure that the motor wi II be a 1I0wed to
start under a heavi Iy loaded conditi on, a centrifuga I clutch
has been incorporated in the motor pulley design. The motor
is allowed to approach normal operating speed, then the,
clutch engages to drive the machine. The momentum devel-
oped by the rotor causes the machine to start even though
several mechanisms may have been tripped. Capacitor start
motors do not require a centrifugal clutch.
The motor pulley operates freely on the end of the rotor shaft
and is held in place by a grip ring retainer. Three ratchet teeth
extend radially from the left end of the pulley (Fig. 5). A
clutch plate hub assembly is set-screwed to the rotor shaft just
to the left of the motor pulley. Pivoted on the plate are two
clutch pawls (Fig. 5).
When the motor is OFF, the pawls
are spring loaded against stop lugs on the clutch plate. When
the motor is turned ON, the clutch plate turns with the rotor.
Centrifugal force causes the clutch pawls tC) pivot on the studs
of the cI utch plate so that the ti p of one of the pawls engages
a tooth of the motor pulley (Fig. 5). The pulley is then caused
to rotate and drive the machine by means of the cycle clutch
pulley.
Motor Pulley
Clutch Plate Hub Assembly
FIGURE 5. Motor Pulley Clutch
The cycle clutch pulley is mounted to a hub in the center of
the powerframe. The hub is supported by a porous bronze bear-
ing and is in continuous rotation with the pulley whenever the
motor is runn i ng .
On eitherside of the cycle clutch pulley hub is a shaft extend-
ing into and supported by the hub (Fig. 6). The shaft to the
left of the hub is called the cycle shaft. The cycle shaft is
driven by means of a spring clutch. The clutch is allowed to
engage whenever a character keylever is depressed. The cy-
cle shaft powers the positioning of the typehead to the desired
character. Its rotation is re$tricted to 180
0
each time a char-
acter prints. After 180 0 rotation the spring clutch is disen-
gaged allowing the shaft to remain stationary. The cycle clutch
is discussed fully in a later section.
2.1