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Topic: EXPLANATION: SERVO vs SERVO MOTOR and driver (Read 968 times) previous topic - next topic

lastchancename

Feb 22, 2018, 11:24 am Last Edit: Mar 07, 2018, 02:27 am by lastchancename
Just to help explain a simple but often misquoted concept.

A SERVO is a closed-loop control system.
It may _not_ be a motor, but typically is*, using feedback to create a stable, deterministic output from the controlled device.
You provide a reference, and the servo control system varies the output to equalise the feedback with the reference value.

* it /could/ be a fluid servo that maintains the specific level in a tank..

Many servo systems utilise MOTORS to delver mechanical output.
It /could/ be a STEPPER motor with step-counting, limits, feedback and drivers to achieve the desired motion control,

OR in ArduinoLand...

the MOTOR might well be a generic DC motor, with attached feedback electronics to achieve a simpler type of low-cost closed-loop control.
This is typically what is inside your *RC 'hobby' servo*.

The reference is a pulse-train which the motor driver 'chases' while moving the motor shaft - providing feedback to the 'closed-loop' driver to maintain equilibrium.
Some gearing is often provided to deliver reasonable torque, speed and stability at low cost.
Ask the right question, which can be hard for beginners, but this doesn't mean that google is broken.
Experienced responders have a nose for laziness, (they were beginners once)... expecting the poster to contribute to the learning experience.

losmi

Okay, could you please post some concrete models/images to illustrate these SERVO types?

lastchancename

#2
May 04, 2018, 06:24 pm Last Edit: May 04, 2018, 06:24 pm by lastchancename
A SERVO is not a type, it is a process.

SERVO refers to a closed-loop control methodology.
In the case of an RC hobby servo, the control process is contained *within* that small box with three wires and an output shaft.

Other 'servos' may be a free spinning motor with an encoder on the shaft. In that case the servo functionality is implemented by the control process between the encoder and the motor driver...
It may control motor speed and/or angular positioning as needed.

...or a cistern that stops overflowing - with a float valve that controls the flow rate and/or on/off valve state.

Ask the right question, which can be hard for beginners, but this doesn't mean that google is broken.
Experienced responders have a nose for laziness, (they were beginners once)... expecting the poster to contribute to the learning experience.

slipstick

Too much theory, not enough practical. To an Arduino beginner the important difference is between a (hobby type) servo and a motor.

A servo can be sent to a particular position, usually an angle. Most servos will only move through about 130-180 degrees though there are exceptions. Typically used for steering things or moving controls.

A motor is a thing that rotates round and round. You can usually control the direction and speed of rotation but you can't position it accurately without some additional equipment , typically an encoder. Often used for driving wheels to make cars, robots etc move.

Much confusion is caused because, for some unknown reason, a lot of Arduino documentation refers to servos as "servo motors".

And to add to the confusion some servos can be converted to what are often called 360 degree or continuous rotation when they spin continuously and you lose the ability to position them. In other words they are no longer servos they are just (geared) motors.

Steve

lastchancename

#4
May 12, 2018, 12:14 am Last Edit: May 12, 2018, 12:14 am by lastchancename
You're welcome to post some extra content ;)
Be careful of your terminology, just because an (RC)servo can be driven to a particular angle, don't dismiss 'servo motors' ...
Quote
A motor is a thing that rotates round and round. You can usually control the direction and speed of rotation but you can't position it accurately without some additional equipment , typically an encoder
...because that's *exactly* what's inside an RC servo!

It's that extra glue that makes a very important distinction.
Thanks for making me clarify that point!
Ask the right question, which can be hard for beginners, but this doesn't mean that google is broken.
Experienced responders have a nose for laziness, (they were beginners once)... expecting the poster to contribute to the learning experience.

slipstick

Be careful of your terminology, just because an (RC)servo can be driven to a particular angle, don't dismiss 'servo motors' ... ...because that's *exactly* what's inside an RC servo!
One the things inside a servo is indeed a motor. But that's not a good reason enough for referring to the whole servo as though it was just a motor.

My car contains a fuel tank but if I talked about going for a drive in my car fuel tank people would look at me very strangely.

Steve

lastchancename

#6
May 16, 2018, 01:38 am Last Edit: May 16, 2018, 01:41 am by lastchancename
One the things inside a servo is indeed a motor. But that's not a good reason enough for referring to the whole servo as though it was just a motor.
Post #2 clarifies that.
Quote
if I talked about going for a drive in my car fuel tank people would look at me very strangely.
As they rightly should !
There *are* exceptions
Ask the right question, which can be hard for beginners, but this doesn't mean that google is broken.
Experienced responders have a nose for laziness, (they were beginners once)... expecting the poster to contribute to the learning experience.

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