Re: [CAD_CAM_EDM_DRO] Is a reduction drive necessary for servo motors?

Organization: Pico Systems
To: CAD_CAM_EDM_DRO@yahoogroups.com
From: Jon Elson <elson@...>
Date sent: Wed, 14 Jan 2004 23:23:59 -0600
Subject: Re: [CAD_CAM_EDM_DRO] Is a reduction drive necessary
for servo motors?
Send reply to: CAD_CAM_EDM_DRO@yahoogroups.com

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Jon

I guess I don 't know how a Servo works. I thought that
it was based on current reversals. Energize it with one
polarity and moves and stays. Reverse the polarity and
it moves. I have not been clear on how it determines which
way to go. So obviously, I have not a full understanding.
At one time I experimented with Automoile Alternators as
stepping motors. As I recall, the stock winding on the stator
drew too much current and I had them rewound with smaller
wire and more turns. They were very powerful but also low
resolution. Don Lancaster wrote and article and there was
a guy using them to do wood carving. It was a very cheap
way to get a lot of torque. Due to manufacturing tolerances,
each step was not exactly the same as the other steps. This
was no problem when you are making an alternator whose
requirement is to put out a pulsating DC current.

Bob McKnight

Bob McKnight wrote:

>Peter
>
>It looks like you would have to know the number of steps
>per revolution of both the stepper and the Servo. I am
>not sure how the servos are rated , but the steppers are
>usually rated in degrees per step or steps per revolution.
>I have been led to believe that steppers tend offer a smaller
>incremental movement than Servos
>
>

Servo MOTORS, themselves, have NO steps. They can move in
infinitesimal units. The encoder sets the resolution of the positions
the motor can be commanded to index to. So, if you have a high
resolution encoder, you get high positioning resolution. I have 1000
cycle/rev encoders on my machine, and counting all transitions gives
4000 counts/rev, so this would be 20 times the resolution of a
standard stepper in full step mode. This is not like microstepping,
where stepper motor steps are broken into smaller units, but there's
no guarantee the motor can move to those smaller increments. The
encoder reads actual position to its resolution +/- some small error,
and the servo drive will attempt to drive the motor to the commanded
position.

Jon


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