Figure 9-14 are normally closed. Since they open only when the motor has reached the limit af travel in one direction or the other, is readily apparent that there will never be a time when both switches are open. Notice that the thermal circuit breaker and the clutch coil are both in the ground (negative) side of the circuit and will therefore be in operation for either direction of travel.
DC Motor Construction
An exploded view of a typical dc actuator motor is show in Figure 9-15. The principal sections of the motor assembly are the armature the field coils and field frame the brake assembly and the thermal-protector assembly. The armature is a standard drum wound on a laminated soft-iron core. also mounted on the brake-lining disk at the other.
The field for the motor is provided by two poles formed to fit around the armature with a clearance of about 0.01 in [0.025cm]. The field coils are double-wound to provide for the reversal of field of field polarity necessary to reverse the motor rotation. Thermal protectors are connected in the circuit for each field(see Figure 9-16).
The brake assembly consists of a coil, a brake armature, and a brake lining mounted on the lining disk in the motor armature. The brake armature is a disk held in place by the motor studs, which pass through slots in the outer periphery of the armature. When the motor is not energized, the brake armature is held against the brake lining of the motor armature by a coil spring. This prevents the motor from turning. When the motor is energized, the magnetic brake coil draws the brake armature away from the brake lining, and the motor is free to turn.
Both ac and dc actuator motors have been manufactured in very small sizes for use in aircraft and missiles
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