Automatic egg turner for chicken incubator, fits 12 eggs. 

Uses an old microwave turntable motor that rotates at ~5 rpm. The gears step down the rotation by a factor of ~1000 so the eggs will rotate only a couple of times per day.

The assembly requires a number of M5x25mm screws and nuts as well as four 16mm diameter, 5mm thick cylindrical bearings for the rotators. Sandpaper or something similar must be attached to the rotators to grip and rotate the eggs. An egg incubator must be kept at ~37.5 C / ~99 F and so a higher temperature resistant plastic might be beneficial. At the very least one should pay attention to where the heat source is.