When designing a stepper motor focuser there are a lot of parameters that you have to think about.
What is the needed step resolution from the stepper motor,
how much do you need that one step move the focuser draw tube?
It has to be designed to use the full stroke (in most cases) of the focuser draw tube,
that is the range of steps that shall cover the focuser from inward to outward position.
You need information about stepper motors and your telescope setup:
You can use my earlier calculation to find out what minimum focus move resolution you need for your telescope: Depth of focus, Astrofriend
Here I try to sort it out:
Type in your data
It start to calculate as soon you change or write new figures in the white or dark red boxes.
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Note:
You use the information on your own risk!
There can always be a mistake in my equations behind the calculations, check that the result is correct.
Let me know if you find something wrong and I try to correct it.
Some calculations are very simple done and not correct in the small details.