[JesseK]

This year, we're going to do a custom gearbox ... somewhere, but not on the drive train. We've been mucking around with 1-1/8" hole cutting for a few weeks now, getting them correctly positioned and straight. In the end, I think we'll use custom gearboxes for a small wrist, a conveyor, or roller intake of some sort.

These systems do have a good argument for attempting custom gearboxes:
Those types of robot systems seem to need the most compactness of any robotic system, and often modifying COTS to can be more difficult or time consuming than designing the gearbox from scratch. With a custom gearbox it's easy to control mounting points and which side of the gearbox the output shaft is on -- with COTS, modifications have to be made to get the same effects. If the manufacturing of the mods goes wrong, new parts have to be ordered -- eliminating any time/headache saved by modifying COTS to begin with.

On another note -- The black FP gearboxes come with very forgiving plastic gears that have giant teeth. While they're probably not great for high-precision or high-power systems, they do seen to find their way onto some very successful robots every year. Hopefully they'll be in the kit again this year so they're legal to use.