It consists of three layers.
At layer 1, the speed is halved.
The speed drops 2.5 times in the second layer.
1.7 layers decrease in 3rd layer

2X2,5X1,7 = 8.5 times the speed has been reduced.

Torque is increased at the same rate. What the torque is not tested. Cordless drill is used for screw tightening and loosening.

The engine used is 12v Johnson engine. Motor diameter 27.5mm, shaft diameter 2.5mm.

1st gear in 1st layer with 0.8M 10T 20PA 5FW --- S10N75H50L2N specification
1st layer 2nd gear 0.8M 20T 20PA 5FW --- S20N75H50L4N

1st gear in 2nd layer 0.9M 10T 20PA 5FWS10N75H50L4N
2nd layer 2nd gear 0.9M 25T 20PA 5FW --- S25N75H50L3N

3rd layer 1st gear 1M 10T 20PA 5FW --- S10N75H50L3N
3rd layer 2nd gear
1M 17T 20PA 5FW --- S17N75H50L3N

1st layer 2nd gear shaft diameter 4mm. bottom ball of this shaft is 8mm in diameter. If the upper ball is
It is 9mm in diameter.
The diameter of the 2nd gear shaft in the 2nd layer is 3.5mm, the lower ball diameter is 9mm, and the diameter of the upper ball (a material such as a ball is used) is 7.15mm.
2nd gear shaft diameter 3mm in 3rd layer bottom ball diameter 8mm.
8mm in upper ball diameter.

I did this from existing materials. I will also share sldprt files for you to do.

Solidworks files:

https://drive.google.com/drive/folders/1nlqQcgT4JIPUVCMwkm47u2QjZjvULEhI?usp=sharing