Newbie plan to install onstep

Pengembara T.

Hi Everyone,

This is my first post here so first of all, thank you to Howard for
creating this project and thanks to all senior members who are helping
other members.

I have a dream to install onstep on my homemade dobsonian mount, need
some suggestion:

1) Motor: I want to get a high builtin gear ratio motor, found
17HS19-1684S-PG100 from OMC stepperonline. Looks like it is not 400
steps/rotation and not 0.9Ampere. It is 200 steps and 1.68A.

What is the difference in terms of power requirement between 0.9A vs
1.68A ? Plan to use a laptop charger. No plan for remote viewing using
a battery.

2) Stepper Driver : LV8729. Is it ok to use LV8729 ? Its maximum drive
current is 1.8A.

And from what I read from this group, we only use around 40% - 70%
from max, so for a 1.68A motor, it should be below 1.2A. Is it correct

If LV8729 cannot be used, what is the recommended stepper driver ?

3) Gear wheel. To get a high reduction ratio, I plan to make some big
gear wheels.

There is an article at instructable to use the GT2 timing belt as
gear-wheel, but in that scenario, the gear wheel is used by the
encoder. Not to drive the telescope.
Source: step 2 from

Question: Can I use a GT2 pulley as a gear wheel ?

4) Microcontroller.
Slow Slewing speed is not a concern for me as a beginner.

If LV8729 can be used as a stepper driver, then my choice for
microcontroller is wemos + CNC3.

If the recommended stepper driver is not LV8729, then can I use MKS Gen-L ?

Question about Onstep operation / astronomy in general:

My plan is to track the moon, Jupiter and saturn.

Currently we use a telescope through the balcony. Our view is limited
to a maximum of half sky.
And the light pollution is a little high. Not many stars are visible at night.

Reading from onstep documentation that we need to align to 3 stars to
be able to track objects.
1) Can I use Jupiter / Saturn as an alignment star ?

2) Can I use static objects like towers, or rooftop building lamps as
additional helpers ? as we can find the GPS coordinate of that tower
and also for the building.

3) Lets say my alignment is wrong because I cannot find enough stars.
What happens if we are forced to continue tracking Jupiter ? I guess
it will be inaccurate / out of field view.

Can I fine tune (to make Jupiter inside the field of view) for 1 or 2
first minutes and after that onstep learn and be able to continue
tracking correctly ?

sorry for my english.

Thank You.

Join to automatically receive all group messages.