Re: What makes a motor a servo?

--- In CAD_CAM_EDM_DRO@yahoogroups.com, "Pete Brown \(YahooGroups\)"
<YahooLists@i...> wrote:

> >>One of the differences between DC servos and DC motors is the

number of

>
> brushes.<<
>
>
>
> Exactly what makes a motor a servo vs. just a DC motor with an

encoder on

> it? I'm curious as I was trying to figure this out last night, but

couldn't.

>
>
>
> Pete
>

I'm very interested in this thread as well.

From what I have been told, there is not difference, but, BUT (big
but goes here)

a DC motor may have a noticable cog, this is where you can feel the
steps as you spin the motor. I have a treadmill motor that is a
really hard cog that needs some force to spin it. Bad.

Many DC motors are rated for high speed, often 5,000 RPM or more where
as a desirable motor will have a speed less than 1,000.

The difference is that you need add gear/belt reducers to get the
speed up. Servos are best when run at 80% of nameplate. (not
exactly shure why, espically if you use a 1hp motor in a 1/8 hp
aspplication)

Servo's with brushes have the brushes in 180.00 degree alignment.

DC motors that are designed for a specific purpose may have the
brushes aligned at an angle that favors speed or torque for running
the motor in one direction only and running in the reverse direction
lacks speed, or power or some such.

Not all motors have ball bearings, but ball/roller bearings are highly
desired for CNC work as the reversing is extreemly hard on sleeve
bearings.

I don't think this is a complete list, but a few pointers that others
have made and I keep in mind.

Dave