I designed a simple baby mobile, since a colleague of mine got a kid, and we wanted to gift him something. 

The mobile contains of 8 arms and a base. The arms have to be glued to the base, otherwise the tolerances are probably too big, and then the arms can fall out easily. 

I have designed two interchangeable arm types. A long and a short one. In my make I mixed them, but when you like you could use also only one type. The diameter with the long arms is around 33 cm. 
You can easily scale the model. I originally designed it a lot bigger and then scaled it down for printing it a second time. The uploaded files should match the 33 cm. 

For the attachment of the base, I used some Paracord, but any string will probably work fine. 
To attach the single items to the arms, I used the inner strings of the Paracord. 

For printing, I have used an adaptive layer height to get the round edged smoothly. 
It took approximately 2,5 h to print and needed less than 70 g of filament.

Print settings:
- Wall loops: 3
- Top and Bottom shell thickness: 1 mm
- Infill: 10 % Gyroid

For my print, some of the outer layers at the bottom didn't attach to the model. I just removed them after the print, but you may have to change your cooling or printing speed a little bit.