ATM Re: Stepper Motors

[cshaw@ghg.net (Charles W. Shaw)]

>Date: Wed, 20 Aug 1997 12:39:10 -0600
>From: JP Roberts <jproberts@sprintmail.com>
>Subject: ATM Stepper motors
>
>I'm making a barn door mount but I don't know anything
>about motors. I've heard that a suitable stepper motor
>can be obtained from a floppy or hard disc drive or from
>a printer. Are these motors typically DC or AC (I'd prefer
>DC obviously)? Does a floppy drive motor have enough
>torque? I've seen a control circuit that looks pretty good
>(www.aegis1.demon.co.uk/gallery/scotch.htm) but is there
>a simpler way?


JP,

I agree with the note that suggested getting a kit from H&R is a totally
simple approach to getting started.  I got one of those a while back just
to see what they were and have suggested them to friends.  They have had
good experiences too.

The kits have 15deg/step motors however.  This, even when 1/2 stepped will
probably be too coarse and you will probably "see" the steps in the
eyepiece.

You need to step your motors at 40 steps/sec or more if you are 1/2
stepping. This means you need to gear things down a bit...  Mel Bartel's
software driven system microsteps the motors (10 microsteps/full step) and
can use slower pulses due to the smaller step sizes.

H&R is probably the BEST source of inexpensive motors.

The circuit to drive the motors is VERY simple.  I have a circuit that I
drew up as part of the plans I put together for building equitorial
platforms.  It uses a readilly available SAA1042 chip (chip costs about $12
from Newmark).  A simple 555 timer (Radio Shack) and some small resistors
and capacitors (Radio shack stuff) and a power supply (12v for 12v motors,
6v for 6v motors) and you are off and running.

If you have scrap disk drives, the steppers in them work quite well too!!!!

Enjoy!!!  Stepers are the best kept secret around for portable scope drive
systems!

Chuck




Chuck Shaw
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