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From: nagle@netcom.com (John Nagle)
Subject: Re: What IS a servo motor, anyway?
Message-ID: <nagleCyKM25.Jqt@netcom.com>
Organization: NETCOM On-line Communication Services (408 261-4700 guest)
References: <38jpku$7uu@powergrid.electriciti.com> <3947pn$aui@manuel.anu.edu.au>
Date: Tue, 1 Nov 1994 04:06:05 GMT
Lines: 21

jaa@gorton.anu.edu.au (James Ashton) writes:
>In article <38jpku$7uu@powergrid.electriciti.com>, mlipsky@powergrid.electriciti.com (Mark Lipsky) writes:
>> What is the distinction between a "motor" or "DC motor" and a SERVO
>> motor?
>> 
>> I have used various kinds of motors in closed-loop position and
>> veloicty applications and I have never been totally clear what the
>> difference is.  Certainly it is possible to use non-servo motors in
>> closed loop applications.  Besides costing more, what does a servo
>> motor give you?  

>I believe servo motors have torque which is almost independent of rotor
>position and the rotor has no preferred positions when power is not
>supplied.  

     Irregular torque from a motor is called "cogging" (because tooth
ripple from gears produces a similar effect), and servomotors are often
designed for minimal cogging.  But it's feedback control that makes a
servomotor.

					John Nagle
