Re: [CAD_CAM_EDM_DRO] servo motors or just a reasonable facsimile?

Tom Murray wrote:

>The Taig factory must be working over-time because my cnc-ready mill
>shipped 2-3 weeks sooner than I expected!
>
>I just received some servo motors for my soon to be delivered Taig
>mill and I am wondering if they really are servo motors or just a
>reasonable facsimile. I was under the impression that if one turns
>the shaft on a servo motor, no cogging will be felt. When I turn
>these shafts, I feel a slight cogging which is much finer than what
>would be felt on a normal permanent magnet motor, but cogging none-
>the-less. Is this normal, or do I have some less-than-ideal motors?
>
>

Well, all motors have cogging at some level. Even ironless-rotor motors
have SOME tiny
bit due to eddy currents in the wire. Unless you will be diamond
turning telescope
mirrors, it is probably of no concern. The mass of the machine will
generally bury the
tiny effect this would produce. A REALLY coggy motor, which feels
almost like a
stepper, would make noticeable step-like action in the movement of servo
systems without
DC tachs or very high resolution encoders. If you will not be using
anti-backlash ballscrews,
don't even waste another minute thinking about it. If you will use good
ballscrews, it
probably won't be a problem, and if it is, you can get better motors later.

Jon