This is a remix of the equatorial mount of SimonRob. Check out his instructables for more details on how to assemble https://www.instructables.com/id/Equatorial-Mount-for-DSLR/
Changes:
-Changed motor to nema 17
-Added another reduction (4:1)
-Changed to chevron gears
-Replaced all screws with M3 (was M2.5)

The reductions are 6:1 then 4:1 so with a standard 1.8deg stepper you get
4800 steps per revolution
76800 steps per revolution with 16 microsteps
1228800 steps per revolution with 256 microsteps (close to 1 arc-second)

I have assembled the mechanics but I have not yet done the electronics or tested it yet, I will use an Arduino with a TMC2208 driver.

I will make the following changes someday:

-Add clutch mechanism to “support”. Now the only way balance the support/camera assembly is to loosen the setscrew witch is not ideal.
-Change the endstop from the manfrotto mount to the “body” to the large pinion does not need to be removed to separate the two.
-Change the main axis to diameter 20x10 aluminum tube with 6804 bearings (20x32x7). It’s a pity the pinion/motor assembly is so rigid without play but there is a ton of torsion in the 10mm tube.

Edit: Only two motor screws can be used. You will need a ball tip allen key for the large pinion set screw.

Edit 22/09/2020:Addes schematic from https://www.thingiverse.com/andrew14/ using two 18650s and a TMC2208 his code is here https://drive.google.com/file/d/1KimSNu2GnHwaGV6QbWR6xXsA_qy4-2Uu/view?usp=sharing