The Mecanum Drivetrain Kit V2 comes with four of the UltraPlanetary Gearbox Kits with HD Hex Motors. This is an entry point into using the REV UltraPlanetary System. There are three UltraPlanetary Cartridges supporting seven different final gear reductions ranging from nominally 3:1 to 60:1. This allows for the right amount of torque for the application at hand. The motor provided already has the pinion gear pressed onto it making assembly of gearboxes easier.
Repeat these steps until you have four fully assembled gearboxes.