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572 RICHARDSON'S BLUEBOOK OF PROJECTION
Starting must be rapid enough for a smooth changeover hut not so abrupt that it may damage either the film or the transmission system. In the case of some projector drive motors the starting torque can be varied by shifting the position of the brushes on the commutator. This is true, for example, of the motor shown in Figure 212. In all such matters reliance must be placed on manufacturer's instructions ; details vary widely.
The same is true of lubrication, both of motors and of transmission systems. The amount of lubricant, type of lubricant and frequency of attention needed by every oil-hole and grease cup in every motor and transmission system now in use cannot be specified in a book like this. In every case manufacturer's instructions are easily ascertained, and should be followed conscientiously.
Where the projector drive motor is a single-phase machine with a separate starter winding the brushes and commutator of that winding, as well as the flyweights that open its circuit when the motor comes up to speed, need very close attention as to cleanliness and proper lubrication.
Troubles and Care of Speed Controls
(19) The centrifugal speed control of Figures 209, 210 and 211 is mechanically similar to the arrangements for supplying current temporarily to the starter winding of a single-phase motor, but under greater strain since it remains in continuous action as long as the motor runs. Cleanliness, especially to provide free motion for the flyweights and to prevent sparking at the centrifugal contact, are vitally important.
The motor control cabinet of Figure 212 needs no attention and gives very little trouble. Any electrical difficulty that may develop is readily found with a voltmeter, since the cabinet contains very few pieces of apparatus and the circuits are simple
When operating trouble is experienced in installations that use motor control cabinets, the cabinets should be interchanged at the first opportunity. This will indicate