1) Start with the 2 Motor Drivetrain Gearbox Motor Plate- the larger of the two plates included in the base kit.
2) Affix your motors to the Motor Plate using four 1/2in long 10-32 button head screws.
3) Install a Flanged Bearing for 1/2in Rounded Hex into the smaller hole of the Motor Plate, and install the larger Flanged Bearing in the larger hole of the Motor Plate. The flanges should face away from the motors.
4) Insert the 1/2in Hex Cluster Shaft into the smaller Flanged Bearing, and insert the 1/2in Hex Through Bore Shaft into the larger Flanged Bearing on the Motor Plate.
5) Install the 1/2in MAXSpline spacer on the output shaft of the gearbox.
6) Install the gears onto the shafts. First, the 52-tooth gear goes on the cluster shaft closest to the motors. The smaller hex bore gear then also goes on the cluster shaft, and the larger MAXSpline gear goes on the output shaft. See the product page to determine the appropriate Wheel Gear Ratio here: 2 Motor Drivetrain Gearbox - Through Bore
7) Insert the 2mm keys into the motor shaft keyways.
8) Slide the appropriate pinions, based on the speed option of your gearbox, onto the motor shafts.
9) Install the external retaining rings on the ends of the motor shafts.
10) Retrieve the Output Plate from the kit, and install a Flanged Bearing for 1/2in Rounded Hex into the smaller hole of the Output Plate, and install the larger Flanged Bearing in the larger hole of the Output Plate.
11) Slide the Output Plate with bearings onto the ends of the shafts of the Motor Plate. The flanges of the bearings should face inwards, towards the gears.
12a) Slide a 1-1/8in spacer between the two plates and line it up with one of the holes near the middle of the plates.
12b) Install a 1-5/8in long 10-32 button head screw through the Output Plate, through the spacer, and into the Motor Plate. Leave this screw loose, for now.
12c) Repeat steps 12a-12b for the other screw and spacer on the top left side of the plate.
13a) Slide a 1-1/8in spacer between the two plates and line it up with one of the holes near the bottom of the plates, on the far outside edges.
13b) Install a 2in long 10-32 button head screw through the Output Plate, through the spacer, through the Motor Plate, and retain it with a locknut at the end. Leave this screw loose, for now.
13c) Repeat steps 13a-13b for the other screw and spacer on the bottom left side of the plate.
14) Ensure that the gearbox is well-aligned, and then begin tightening the four screws holding the Motor and Output plates together.
Note: Do not tighten one screw all the way tight before tightening the other screws. Alternate between tightening all of the screws a little bit at a time.
For best results, spin the gearbox by hand between tightening each screw until you have completed assembly!