Each gearbox is built from scratch and then tested for speed and torque. Flat layouts only (gears are on the same plane) for better visualization. Enjoy!

00:00 2speed
01:09 2speed with driving ring
02:31 4speed
04:02 6speed
05:58 8speed with range change
08:29 12speed with splitter
11:48 all gearboxes sidebyside
12:09 graphs

Key Lego parts used in this video:
Driving Ring 2L [6539] https://www.bricklink.com/v2/catalog/...
Axle Connector 2L [6538c] https://www.bricklink.com/v2/catalog/...
Gear 16 Tooth with Clutch, Smooth [6542b] https://www.bricklink.com/v2/catalog/...
Changeover Catch [6641] https://www.bricklink.com/v2/catalog/...
Changeover Plate [6631] https://www.bricklink.com/v2/catalog/...
Driving Ring Extension [35186] https://www.bricklink.com/v2/catalog/...

Check out a great resource on Lego gearboxes:
https://www.lugnet.com/~3813/