[Joe Ross]

On the other hand, some teams have very similar arms from year to
year, and add different attachments. Two teams I can think of off the
top of my head are 60 (kingman) and 173 (rage). I think they've
figured out that practice time is more important then time spent
reengineering a whole new robot each time.

So, it becomes the same as the gear box. They build 20 arms, with easy
mounting hardware on each end, and sell them in the offseason. Then
when the 6 weeks start, you plop that arm on the base you've just
built with the gearbox from Andy, and build a ball grabber, or
innertube grabber, or whatever, put that on the other end of your arm,
practice for 3 weeks, and do very well.