Electric servomechanisms

Deals solely with electric servomechanisms of the type intended to control the aiming of weapons such as guns, radar aerials, submarine microphones, etc. All these are position-control devices and one special feature is that there is a low permanent torque with violent transient torques of extremely short duration, while, throughout, high accuracy of positioning is essential. A weapon servomotor, therefore, needs a low average power, but transient high powers are required at intervals. In normal electric motors, the output power is limited by the temperature rise, but this limitation does not apply to the servomotors for controlling weapons, and, in consequence, the magnetic characteristics of the motor become the main factors. Electric servomotors are preferred to hydraulic motors because of the greater acceleration obtainable, and the fact that greater accelerations than they can produce would strain the gearing. Although rotary amplifiers and thyratrons are used to drive servomotors, it is forecast that magnetic amplifiers will be widely used in future. Temperature variations over a wide range have a negligible effect on the operation of electric servomotors, while such machines need only little maintenance and are stable over long periods.