So, after months of work, I have an OnStep controller, as I explained in this post.
I tested it under the stars, and for short exposures, it works well.
But I continue to try to push further to see what the limits are.
The motor is the MPJA NEMA11 with an 18:1 gear head, and 1:1 belt and pulleys to the worm gear.
The worm period for the mount is 480 seconds.
So I took an exposure that is 960 seconds (two rotations), of Albireo (with a known distance between A and B of 34 arc seconds). The result is attached.
There is no PEC yet on this mount (neither with a sensor, nor with parking only).
Look at the two orange stars on the left below center.
There is a large wave which is due to periodic error.
The question is: what are the smaller fluctuations?
My configuration is posted on the link above.