List of used elements:

Electronics:

• 28BYJ-48 stepper motor with ULN2003 driver board (5V)

• ESP8266 D1 mini / ESP32 S2 mini - both are produced by for example Wemos - if you want a different one, then check the pin distance both horizotnal and between adjacent pins, because PCB is designed for those 2 boards specifically; you can ofc redesign the PCB to match your microcontroller of choice; I suggest picking one with Wi-Fi so that you can implement a wireless control viayour smartphone for example

• micro-USB breakout board (can be USB-C but then you have to match the power delivery standard by pulling down one pin of this socket, so I chose more straighforward approach with micro-USB)

• goldpin sockets (or you can use anything else to connect cables)

• On/Off switch (whichever you like, I had a round lever toggle switch around so I took that - ofc adjust the mounting hole accordingly if you use different one)

• bunch of short cables with isolation

Mechanical:

• bunch of M2.5 screws [different lenghts from around 6 to 12 mm] and nuts [5 mm diameter] - I used hex with pretty high cap, but if you can find some with smaller caps it's even better

• 6 mm diameter, 2 mm depth neodymium magnets

• one long (cutting needed) or a bunch of around 8 mm long stainless steel rods (3 mm diameter)

• 3x7x3 mm ball bearings (both the bearings and the rods sizes can adjust to your needs by editing the model ofc)

• sanding paper in case your 3 mm rod tolerance is bad and they are too thick to fit throughball bearings

• metal screw inserts - used to screw down the lid to the case box (soldering iron can be used for convenience or you can just heat them over a flame from lighter and precisely place in the holes)

• hot glue or any other adhesive of choice - I used it to glue down the micro-USB board to the case box so that it doesn't move when I plug the power in

• cyanoacrylate glue to glue down the magnets in their sockets

General Idea

So I ofc use this to wind up my automatic watch when it's not in use. The Wi-Fi board allowed me to use for example Arduino IoT Cloud to build a simple smartphone dashboard where I can control my winder via Wi-Fi (thanks to cloud it's "global" not only local). I programmed it in Arduino IDE, but I won't be giving out he code for now as probably everyone would like some different functionality and with the usage of AI everyone can programm boards these days.

In the design I use 5V micro-USB power supply taken from and old samsung phone. Better idea is tu use slightly higher voltage power supply and add a 5V stabiliser to the circuit, but I didn't think about that in original design. I leave it for you to chose. If you have stable 5V source then I think my design is ok, but stabilizing is always a better option.

PCB DESIGN:
<i will add it shortly via google drive link to KiCAD files>

Assembly:

It's pretty straightforward. Given you have all needed elements or your own substitutes then you can just look at the photos and place the elements as they are shown. Here again I leave the microcontroller fun for your own invention. 

1. First I would solder the PCB to have it ready.

2. Secondly I suggest to melt in the screw inserts into the CASE BOX.

3. Next take the INNER RING and screw down the HALF RING. Carefuly glue the ball bearings inside their sockets.

4. Take the MIDDLE RING and mount it to the INNER RING using the steel rods through bearings so that they rotate in respect to each other very smoothly.

5. Do the same thing with OUTER RING and mount it to the MIDDLE RING - now you should have all 3 RINGS with smooth, planetary motion.

6. Take the BACKBONE, screw down the OUTER RING to the LID, screw the stepper motor, place down the BACKBONE on stepper motor axis (do not glue it, it holds tightly and this way it's easily replacable if motor dies)

7. Now you can mount the inner system to hold the watch itself, glueing in the magnets, screwing down the side supports etc.