Re: ATM stepper clock drive

["Bill T." <twentiethwave@hotmail.com>]

I prefer microstepping, but it is also possible to achieve extremely smooth 
operation from full and half step drives.  If you hook up a particular 
stepper to a particular drive and run it at different speeds you'll find 
that some speeds are very smooth, and other speeds are rough.  The trick to 
getting smooth operation from a non-microstepping motor is to first discover 
a (usually narrow) low speed range over which the motor is very smooth, and 
then design the mechanical transmission such that the stepper runs at 
known-smooth speed during normal operation.  Press the motor frame against a 
hard table top along the shaft axis to simulate the damping effects of 
mounting.  Load inertia has something to do with the exact speed/roughness 
characterics, but in general if a motor runs smoothly at some speed without 
a load, it will run even smoother with a load.

Of course this applies only to equatorial type mounts, where the motor only 
has to run at one speed most of the time.  If you need the speed bandwidth 
required by an altaz mount, use microsteppers.

Calculation has a lot to with engineering, but empiricism goes a long way 
too.

Bill T.



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