[Kevin Sevcik]

It does in fact cost more. 4140 hex shaft from McMaster has a -.008 tolerance. Any hex broach you'd care to find is going to have a +something to -.001 tolerance or so. So if you're interested in inexpensive product, you buy the preformed hex shaft, round it off, and worry about something else. If you're worried about fit issues that only matter at the extremes, you buy larger stock, machine a hex on it, and charge a heck of a lot more for the trouble of having to use 2 machines on a simple shaft.

As to the rapidly reversing heavy loads... I'm talking about a 140 lb robot with 2 CIMs per side and ultra grippy tires driving at a top speed of 15 fps across the field and then instantly throwing the motors into full reverse. Repeatedly. And that's assuming the robot stays rubber side down. And even then, I think you're more likely to shear a key, or snap a chain before you ever dent that gearbox. So like I said, not the kind of load commonly encountered by FRC robots, and anyone who's planning on that kind of loading is probably already looking elsewhere for their trannies.