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From: gbt@sequoia.cray.com (Greg Titus)
Newsgroups: sci.astro,sci.electronics
Subject: Re: Stepper Motors
Keywords: stepper,  motor
Message-ID: <233504.20922@timbuk.cray.com>
Date: 7 Nov 90 05:45:41 GMT
References: <1436@fs1.ee.ubc.ca> <10700@milton.u.washington.edu>
Sender: gbt@sequoia.cray.com
Organization: Cray Research, Inc., Eagan, MN
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In article <10700@milton.u.washington.edu> whit@milton.u.washington.edu (John Whitmore) writes:
>In article <1436@fs1.ee.ubc.ca> shawnd@coho.ee.ubc.ca (Shawn Day) writes:
>>
>>We are planning on building a stepper motor drive system for tracking
>>& slewing a 12 1/2" telescope.
>>
>> ...  we need to find a source for 
>>inexpensive stepper motors.  Our current calculations indicate that 
>>we need motors with about 260 oz-in torque and a speed of at least 40 RPM.
>>
>	260 oz-in of torque is a LOT of torque for most small (cheap)
>stepper motors; for that much torque, the shaft diameter is 3/8"
>and used ones go for about $70.  Also, 40 RPM is very slow for a
>stepping motor; typical speeds are 300 RPM and up.  So, it looks like
>you should consider different gearing (finer screw on your worm drive?).

John's right.  Shawn, a smallish but useful article on stepper
motor driver circuit design and associated topics appeared in
Sky & Telescope I believe last year.  Check the Reader's Guide
To Periodic Literature.

greg
--
--------------------------------------------------------------
Greg Titus (gbt@zia.cray.com)             Compiler Group (Ada)
Cray Research, Inc.                               Santa Fe, NM
Opinions expressed herein (such as they are) are purely my own.