Hi! I created 3D printed gearbox which I will use in my robot but you can use it anywhere you want.

Supplies

1x BR2212 1000KV BLCD motor

1x 8mm shaft 500mm

4x Ball bearing 688ZZ

1x 3mm shaft 55mm for BLDC motor

5x 3mm screw

Step 1: 3D Projecting

First I created 3D model of this gearbox. Gear ratio is 1:9 it means I used 2x10 tooth gears and 2x30 tooth gears.

Step 2: 3D Printing and Assembling

Next I sliced model and printed on my 3D printer it takes something around 5 hours then I placed ball bearings. There is a important thing. My BLDC motor had too short shaft so i repleced shaft to longer from old cordless screwdriver. There was another problem the gears was rotating on shaft so I driled 3mm holes for screws to keep it in one position. The shaft is 8mm but one of this gears has hole 6mm to be more stable, so on the lathe I cut extra material from shaft. Next i assembled everything in one part. At the end I added some 3d printed washers betwean gears and bearings.