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how do servos maintain a certain position?

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how do servos maintain a certain position?
-what components are used?
-can this be done to all motors?

There is typically a potentiometer inside that is connected to the output shaft to measure the position and a closed loop controller to maintain the position to the target value which is a function of the width of the pulse received by the servo.

Yes, you can do this with other motors if you add a position sensor of some kind and a closed loop controller.

how does the closed loop controller maintain the motor in one direction?
how does it change the voltage applied to the motor exactly with the width thing(do you mean PWM)?

Have you googled servos, servomotors, closed loop control and then other terms you find when reading.

One problem in trying to give you an answer is that there are a number of different methods to control the position of a geared motor output. So search and read then search and read some more.

A "servo" is made up of four things:

1) A motor or other actuating device.
2) A sensor of some sort (potentiometer, optical encoder, magnetic field sensor, etc.)
3) Driving circuitry for the motor (typically an H-bridge.)
4) Controlling logic to read 2) and apply output to 3).

Exactly how 4 is done depends on the type and manufacturer of the servo. A pneumatic servo for rock extraction in a mine is different from a battery-powered rudder servo for an RC plane :-)

In general, the servo controller will read the position, and compare to the desired position, and then apply more force to the motor (higher PWM duty cycle) the further away it is from the goal. Look at the Wikipedia entry for "PID controller" for the next step of learning about this.


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