Ya, I hear you. If you have two motors on your elevator, it’s nice to be able to use those motors to also power the elevator wrist.
Fundamentally, we’re talking about using two motors to power two different degrees of freedom - a differential slaves these motors together, but it doesn’t reduce the total number required. What I was trying to communicate was that doubling up on motors for one mechanism is less mandatory because each motor can now provide so much power. If you can design/build competitive mechanisms powered by only one motor, than the differential doubling up on power is redundant/unnecessary.
Lets say we both build robots with elevators + wrists. I put a falcon on the elevator, and separately a falcon on the wrist. Maybe I spend extra time to make my elevator + wrist + manipulator really light weight (improving the power/weight ratio on the side everyone seems to forget about). Ultimately, this combo should have enough power to move the manipulator anywhere in it’s range of motion within 0.75sec (or whatever fast made up number). Even if you have designed a differential elevator with two falcons manipulating the elevator + wrist, your power advantage is only going to marginally improve your manipulating speed/maybe start to approach a controllability limit and you have incurred additional complexity/design/software/maintenance risk.
Maybe an aside, but the longer I’ve been in frc, the more I’ve come to value reliability in a robot. (This hit me hard back in 2013 when the 33 robot was having issues/died on Einstein.) If you have a mechanism that fails in a single match, that can often be enough to cost you the match/top 8 spots, an elimination run etc. Conversely, having a robot that’s mostly maintenance free is worth an unquantifiable amount (I recall instances during the round robin where you only have time to change the battery, then have to get back on the field.) That’s why I want to be supremely confident in the reliability/controllability of any novel/especially complex mechanism before putting it on the field. These types of mechanisms require so much prototyping/design/testing bandwidth that my personal preference is to (1) minimize these to 0-2 per robot and (2) only execute on them when they will create some kind of significant competitive advantage. 971 only considered the single stage differential elevator because we were confident that we could design/build it with basically no risk (double timing belt loops, one terminates on the carriage, one around a pulley on the wrist.) Once we started talking two stages, we were really concerned about the long cable lengths and general controllability.