From: "Duncan Radbourne" 
To: 
Reply-To: "Duncan Radbourne" 


Hi Chaps

I'm here in England and Am a big fan of stepper motors , am just modifying
some autostar DS motor units to run steppers !!! cos I like them best !!.

back to the thread , if the stepper is geared Via a worm It wont loose its
position much if the power is turned off , .


Regards

Duncan Radbourne
Secretary
West Of London Astronomical Society

Rem. Difraction limited is another way of saying "pay  more and accept
less "
----- Original Message -----
From: "Dwight K. Elvey" 
To: 
Sent: 30 January 2003 21:36
Subject: was: Re: ATM motorizing scope questions


>
> >From: "Bob May" 
> >
> >Only one problem with this thread tuning into a discussion of DC motor
> >problems is that the motor described in the original post is a stepper
motor
> >which doesn't get pulses to move it but rather DC levels which get
switched
> >about to move the shaft of the motor!
> >If you remove the power from a stepper, it immediately loses its position
if
> >the motor is moving something.  There's a whole different process to move
a
> >stepper motor than from almost any other motor.
> >Bob May
> >http://nav.to/bobmay
> >bobmay{at}nethere.com
> >NEW! http://bobmay.astronomy.net
> >
>
> Hi
>  This is not always true. There are two kinds of steppers.
> Some have permanent magnets and will hold ( with reduced
> torque ) their position with the power off. Others require
> the power to always be on to hold. This also assumes that
> one stops at full steps and isn't micro stepping.
>  Even those that have the permanent magnets require the step
> to finish and the stepper to stabilize before removing the
> power. Removing the power early will often cause it to
> jump.
>  Anyway, I wasn't following the original post. I came in
> when a fellow said that he'd made a DC control with PWM
> and he was wondering why it was singing. He was also wondering
> why it didn't have as much torque as low speed as at full
> speed. I then went into describing the right way to control
> a DC motor such that it will deliver full torque at low
> speed.
>  One fellow mentioned that one could use a LM317 but that
> has the same issue that you need the feedback of the current
> to get the desired voltage to speed type control.
> Dwight
>
>
>

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