Pretty much just stripped bildrule's mount down to the very basics, making it more or less a pillar with an Arca base, so you can use a tripod to polar align it, and a 3/8" bolt hole on top so you can use a cheap ball head to mount the camera. (I sized it for https://www.amazon.com/Koolehaoda-Rotating-Panoramic-Ballhead-Release/dp/B0CB5LK4LV/ but there should be plenty of other options.) It's doing pretty well with my old Rebel T5, but I have no idea what the actual weight capacity is.

The little tube on the edge was theoretically for a quick eyeball polar alignment, but I missed that the tripod head I was mounting it to blocked my view through that.

I haven't come up with a good electronics housing yet, because after some frustration at a couple of digistamps, I just upgraded to a Nano, which now has me wanting to bring off an output to trigger the camera, and maybe a speed adjustment so it can also be a planetary tracker. I'll probably end up with a box mounting to a tripod leg to hold both boards and a 9V battery.