I don't know why but i really like to design gearboxes. This one has a ratio of around 126:1 and uses herringbone gears. It works pretty well and can be used for whatever purpose you want( use grease for better performance )
I also included .f3d and .step files so you can easily edit all the parts.

Parts list

1x 6V Brushed DC Motor 24mm x 30mm
( https://pl.aliexpress.com/item/32709347843.html )
2x 2mm x 68mm rod
10x small 3mm screws
Optional grease for gears

1x Gear 36-9t
1x Motor Gear 20t
1x Top Gear 36t
2x Gear 23-9t
2x Gear 36-22t
1x Bottom Plate
1x Top Plate
1x Case with or without holes

Youtube video https://youtu.be/7-ai_ZqaiQE

Make sure your 3D prints don't suffer from elephant foot , because that would increase the diameter of gears making them unable to spin correctly.

Creality

Ender 3

No

No

200

20