Basically a servo consists of a Motor (DC or AC), a potentiometer, gear assembly,
and a controlling circuit. At the beginning, we use gear assembly to reduce
RPM and to increase torque of the motor. At initial position of
servo motor shaft, the position of the potentiometer knob is such that
there is no electrical signal generated at the output port of the
potentiometer. After that an electrical signal is given to another input
terminal of the error detector amplifier. Then there's difference between
the two signals, one comes from the potentiometer and the other comes
from other sources, will be processed in a feedback mechanism and output
will be provided in terms of error signal. This error signal acts as
the input for motor and motor starts rotating. Now motor shaft is
connected with the potentiometer and as the motor rotates so the
potentiometer and it will generate a signal. So as the potentiometer’s
angular position changes, its output feedback signal changes. After
sometime the position of potentiometer reaches at a position that the
output of potentiometer is same as external signal provided. At this
condition, there will be no output signal from the amplifier to the
motor input as there is no difference between external applied signal
and the signal generated at potentiometer, and in this situation motor
stops rotating.
