Author Topic: WHAT IS A SERVO????????  (Read 2485 times)

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Offline KK428Topic starter

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« on: April 21, 2017, 05:22:22 PM »
I am just a beginner trying to build my first robot. I did a wiki search but as always it is complete nonsense to anyone that has not got a masters degree in robotics! please put your answer in dumbest form. :-\

Offline FIFO

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Re: WHAT IS A SERVO????????
« Reply #1 on: April 25, 2017, 03:47:00 PM »
    A servo mechanism is basically an actuator (such as a motor) with a closed loop feedback system. What this means is that the servo controller can "know" the absolute position of the actuator at any time. In hobby electronics, one often encounters small servomotors whose position can be controlled by sending a control pulse of varying length (PWM).
    Now let's say, for example, that you have a sonar distance sensor attached to a servo on the front of your robot, and you want the robot to turn the sensor to the right to see if there is a clear path. One could use a microcontroller to send a pulse to the servo commanding it to turn 90? to the right. What's nice about this is that the control electronics in servo will make sure that it gets to that exact position and stay at that position, even if the sensor is bumped. Now of course you can do far more complicated things with this setup, such as having the servo constantly scanning back and forth so that the sonar can create a 2d distance map ahead of it, but this is just a basic example.

    If you want to learn more about hobby servos, I suggest that you check out this article by Sparkfun: It is comprehensive and very easy to understand. The Society of Robots also has its own page on this too:
« Last Edit: April 25, 2017, 09:51:43 PM by FIFO »

Offline Doug83

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Re: WHAT IS A SERVO????????
« Reply #2 on: August 13, 2017, 03:05:02 AM »
A servo is a positional motor: you tell it to rotate (a shaft) or move (a linear actuator) to a certain position, and it will try to do that.
A servo mechanism is basically an actuator (such as a motor) with a closed loop feedback system. ...
Also the term "servo" indicates some type of feedback control loop, but how far that feedback extends makes a big difference.

R/C servos and "CNC-style" servos are both called "servos", but they are not the same things.

When talking about smaller hobby robots, usually the term "servo" refers to the remote-control toy servos.
Most remote-control (or R/C) servos don't really constitute a closed loop, since they don't report their position back to whatever is controlling them.
They will try to move to the indicated position, and will try to maintain the position under varying loads, but if they're wrong you still can't tell just from the servo alone.
When building toy robots, hobby servos are easy to use mainly because they are inexpensive and because they come in a design that is convenient to use.
Stepper motors can work too. They can deliver much higher constant power levels, but they are not as compact or as inexpensive.

In general--R/C servos are built for intermittent use and light loads.
They are designed as control motors for small toys, and they work well for that.
Industrial robots don't use them however, because of the lack of true closed-loop control.


Industrial "CNC-type" servos use a motor coupled to a positional encoder.
Every time the servo's motor is told to move any distance, the movement is constantly verified by the positional encoder and that result gets reported back to whatever is controlling the whole servo.
Also--at any time you want, you can have the controlling computer ask the (industrial) servo what its current position really is, and it can tell you, by checking the positional encoder.
So the whole time a CNC-style servo is being used, it is always being verified that it is in the exact correct position that it should be.
If anything moves the servo when the servo's motor is not running, you can still find that out too.

Lastly: among industrial servos, the term does not imply any particular type of motor.
There are servos made with brushed-DC motors, brushless motors (3-phase BLDC) and stepper motors,,,, as well as pneumatic and hydraulic motors AND linear actuators using any of these as well.

Offline digibloke12

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Re: WHAT IS A SERVO????????
« Reply #3 on: August 18, 2017, 05:46:21 AM »
I'm new, too, and when I was just starting, I saw Power Motion: An Introduction to Servo Motors and barely understood something.

To cut to the chase, I did a little bit of research after that, and based on what I was able to understand one of the references (Wikipedia), Servomotors are an automatic device which reacts on negative feedback? Hope my understanding served me right. Well, I've got a long way to go!   ;D