What is a servo motor?

[ennma]

Hello there, this is off topic, but what does it do? a servo motor that is. thanks

Roy

[christopher_wolf]

Basically, it is a motor that will hold an anuglar position for a given signal. To do this, it has various control and feeback circuits. The simple ones have just a potentiometer that increases in resistance in one direction inside as well as a normal electric motor, hence providing an error signal for the controller and the motor will shut off once it reaches the desired position. Most of them only go 1 Pi grad or half a total revolution (180°); they are also proportional, i.e. the large the arc it has to encompass, the faster it will go to approach and close with the steady-state command angular position. The simplest servos simply respond to a single logic level being held high for a controlled period of time. The longer the pulse, the more the servo moves in accordance. Given that you know the rate of the motor and the servo motor's response (a transfer function would be most useful), you can accurately predict where the servo will stop for a given pulse under any loading conditions.

HTH

[Kyocera]

http://www.seattlerobotics.org/guide/servos.html

[christopher_wolf]

Yeah, but where are the detailed specs, diagrams, and transfer function?

[skitty4gzus]

told you these folks were smart. Check out what Chris just said. So much of what you said about servos totally made me feel extremely stupid. I guess I will stick to my background in home theaters and distributed home audio. Oh, I am also a carpenter as well. I can hold up in a conversation about those topics but not about servos.

[440roadrunner]

There are millions of electromechanical devices that can be called, in loose terms, a servo motor, and in the broad sense of the word, "motor" does not have to mean angular rotation or electric powered.


One example, is an automotive "cruise control." The vacuum unit, if that's what your vehicle uses, can be loosely termed the "servo motor." On my cars, it is a vacuum can that operates the throttle through a linear linkage.

The unit takes inputs from the transmission/speed indicator into the cruise controller, loosely a "servo amplifier"


Again, in loose terms, not necessarily a cruise control, there is SOMETHING in the circuitry that serves as a reference, and something else (the driven unit) that contains a device which generates a signal for the amplifier, which results in an error signal. This error changes phase and amplitude as the mechanical device deviates from the reference, in this case, speed. The amplifer, in most configurations, strives to "amplify" (operate) the mechanical link until the error signal dissapears to near zero. In the case of speed control, the error, of course, is reference to the speed selected.

Back in my RADAR days, many antenna control circuits were operated in those days by a modified "syncro" unit, and through an amplifier, actually drove mechanical sweep circuits. These could be interface, on shipboard units, with the compass repeater devices.

Servo's in general can be electric, air, vacuum, hydraulic, and probably a few other types.



Tell us more about the context in which you asked this question?

[ennma]

Thanks alot, I read the link just was not sure what servo does in actuallity, but I understand, its a device that we can control the angular position of the shaft.

thanks

[jdhurst]

I pulled apart a 2.5 inch hard drive that had failed. The head is a servo motor. The heads are on a pivot. Fixed to the heads behind the pivot is a wide structure holding a coil. All of this assembly pivots very, very freely. Then underneath the coil is a piece of metal (inside the case itself) and overtop the coil is another like piece of metal with a relatively powerful flat magnet fixed to it. The coil is precisely suspended in between and bingo, there is your servo motor. ... JD Hurst

[Kyocera]

Uhhh, JD were we bored today?

[jdhurst]

Uhhh, JD were we bored today?

Bored Nope. I don't get bored pulling things apart. It is from doing that over the decades that has taught me how to take important things apart and get them back together again
... JD Hurst

[christopher_wolf]

2.5" HDDs are awesomely fun to disassemble. There are quite a few novel things to pick up just by looking at the internals of one.

[joester]

I've been making a speaker out of one.

Just need a reliable connection from the read head to the cone.

It actually works if you mount the cone so the head isn't parked against the magnet.

I figure it'll make really cool "computer speakers" for the desk once I get the bugs worked out.

Joe

[ennma]

what the hell happened here? started with servo motors, and it's turning into, computer speakers from hdd.

man shouldn't have drank that coffe, its now 5 am and I can
't sleep,

Madona a mia

ennma

[christopher_wolf]

See? Told you that 2.5" HDDs can be fun. Now somebody wants to make computer speakers out of them.

Heck, I have a bunch of dismantled HDDs around here in various states of entropy myself. 2.5" HDDs, a few old ~700MB drives, 10K RPM spindles, A microdrive, and almost all of the parts from a very large HDD by Fujitsu....All great fun.

[Dngrsone]

Ah, I remember the good old days when one could actually repair their hard drives... not that it was any fun, mind you.