For fun i have create an 5:1 planetary gear with ball bearings, it's running but not perfect.
If you want use it please remember that it's better to do some modifikation.
Printed with an Prusa i2 0.5mm nozzle
eletric motor = Johnson HC785LP/HS
2x 626ZZ ball bearing ( 6x19x6mm)
6x MR63-2ZZ ball bearing (3x6x2,5mm)
3x screw M3x 35mm
5x nut M3
3x screw M3x 20mm
3x stop nut M3
2x screw M4x 8mm
1x rod 6x 40mm
2x grub screw M3x 6mm
6x washer M3