When I have asked about this previously (several years back now), it was stated that these limits are only for running 'spinners' in Grade 3 arenas and lower, aka the live event arenas that aren't fully sealed and have a net/fabric roof. If you're running a robot in a spinner friendly arena then the only parameter you really need to measure is tip speed (250mph max for all weight classes, 125mph for MW and HW machines at EXR I believe).

My featherweight Drumroll currently has a drum that is about 4kg and spins at 10,000+ rpm. I've never had to speak to an EO about it, or any of my spinners, attending prior to an event, and they have all exceeded one or two of the three limits stated in the rules. So what the rules technically say is that if you turn up to, say, a Robots Live event with a vertical spinner feather that has a 1kg disc, 400mm in diameter spinning at 450rpm, you should be allowed to run it. But in reality, that is less of a spinner and more of a rotational flipper. I've never understood why the rules haven't been updated to clarify this as it reads really oddly for a newcomer when they've watched featherweights with 3kg discs spinning at 5000rpm smashing into stuff.