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What is the difference between a SERVO and a DC MOTOR?

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Newbie level 4
Nov 26, 2012
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Hi everyone,

I a trying to turn a knob and I want the solution to be as cheap as possible and use as less power as possible.
My know turns 45 degree to close and 45 degrees reverse to open. My questions are:

1- Do I need a servo for this or a motor? Please detail advantages/disadvantages?
2- How would I know how much torque or power I need to make sure I buy the right motor or servo? I have a scale at home :p can that help me?


Servo would be a lot easier. It has a built-in gearbox to give high torque, and also includes the circuitry needed to control the motor and set the exact position.

To answer the question in the title:
Servo = motor + gearbox + electronics to control the motor.

Thanks for the input godfreyl.
How would I know what kind of a servo I need to be able to turn a knob? Of course it has to be powerful enough to turn the knob or maybe use a poly system to turn it in a compact space. I have a scale at home that I can use to push the knob :) would that help me anyhow?

If the degree of rotation is less then 270 degrees, put your "knb" on the shaft of a pot. Now you can transfer your degrees of turning into a voltage. At the other end you have your output shat connected to a similar pot, which then gives feedback of how many degrees the shaft has turned in the form of a voltage. You now need a motor and gearbox and an amplifier. The amplifier amplifies the difference between the knob voltage and the shaft voltage and uses this to power the motor, which will turn the shaft until the difference voltage (the "error") is zero.

Servo will be a better option because u can control it with a pwm signal generated by microcontroller with axact angle
It will also give u a better torque
Light in weight
Small in size

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