Hello,
I bring my stone to the building of this project, or my grain of salt, it is according to the opinion of each! ...
For my DIY that requires a regular movement or a frequency, I use the small mechanical watering programmers which offer pre-settings (in frequency and duration), and can be easily diverted from their intended use by a small mechanical DIY.
In this case, once we have determined the frequency and duration of watering, there is a small mechanical valve that turns 1/4 of a turn at the opening (frequency), then another 1/4 of turn on closing (duration), and the reduction of which is significant enough to cause a mechanism either door opening or hatch, or to rotate something.
It's still plastic but quite resistant and by adapting this type of programmer to a more solid mechanism, I think we can train a much heavier object.
This type of product costs 20 to 30 € depending on the quality (or brand), works with 2 small 1,5 volt batteries, is waterproof against rain and humidity, the hourly accuracy is very correct (I tested), and the autonomy is about 1 year but you can easily add an additional battery pack for more autonomy.
I have just recovered this one, and on reading the technical proposals, it seems to me that it can be suitable for a mini solar tracker with a suitable choice of frequency and duration which each time produces a rotation of 1 / 4 turn of the ball valve:
I indicated in yellow the direction of rotation of the sphere and the red point indicates the axis.
Fixing a small pulley on this small sphere is simple, with possibly an additional reduction to have more torque.
It remains to find the right combination of frequency and duration for the rotation of the sphere exactly following the movement of the sun in steps. I haven't thought about it yet, but if someone finds it instinctively, I will test to tell you if the rotation of the sphere follows the sun!