I'm sorry for you guys to write this in English, my written German is not so good. I do read German, but I will respond in English.
This planetarium (a mechanical model of the planets in our solar system) consists of 6 planets (Mercury, Venus, Earth, Mars, Jupiter and Saturn) who are in orbit around the sun. Each planet has it’s own Raspberry Pi Zero W, a stepper driver (Adafruit Motor HAT) and a stepper motor (NEMA 17).
On a website any date can be entered after which the website sends out a string with the positions for each of the planets. The Raspberry Pi picks the position up via wifi, calculates the position and takes the steps necessary with the stepper motor.
The whole story (and pictures and movies) can be found at: https://demoor-orrery.com/en