That answer about the plate on the back of the magnet strikes me as a little bit odd.
If a magnet is defined as a pure chunk of magnetic substance, then to use ordinary rare earth magnets, you'd have isolate the actual magnetic material by removing the plating—because plating material is not on the allowable materials list. (That's a
horrible idea for many reasons, and would be an absurd ruling.)
But if a magnet can have other stuff attached to it, what's permissible? A fridge magnet has a label, or paint—and indeed the "magnet" part is really a polymeric substrate with ferromagnetic inclusions. And as noted above, rare earth magnets are almost always plated.
So why can't hard drive magnets have a backing plate? They're still magnets, aren't they? Or are we reverting to the absurd definition I gave initially? I'm not seeing a middle ground either—the rules don't imply anything about the definition that might be used to discriminate between different varieties of magnets.
On a related note, FIRST has been quite consistent this year in defining components in terms of the way they're sold. It would follow that if these things are
sold as magnets, then they would be considered magnets. So, is there a vendor that sells these (as COTS items, to the public), either after having salvaged them from hard drives, or as the supplier to the hard drive manufacturer? If you can find
such a vendor, I think it's pretty clear that FIRST's ruling is not correct for all cases (again, unless we're falling back on the discredited definition).
But if you can't find a vendor selling
the exact hard drive magnet you want to use, then from a material utilization perspective,
you're actually using a modified hard drive (which is not in <R92>). At that point, you need to know whether or not FIRST is operating with a dualistic definition—something like "either it's sold as a magnet, or is inherently a magnet"—or if they're just picking one criterion and sticking to it. You might therefore want to ask the Q&A.
If this were to come up at inspection, I'd say giving the team the benefit of the doubt would be appropriate. I'm not sure how to interpret FIRST's intent based on that Q&A, and I don't think we can expect that of a team in this circumstance. (The team shouldn't suffer because of a rule that was not clear, and for which they executed a reasonable attempt at compliance.*)
By the way, odds are it's not going to be possible to remove that magnet from its plate without something horrible happening to the magnet. It's probably epoxied to the plate, and there aren't many solvents that can dissolve that in a reasonable time. Rare earth magnets are very brittle, so trying to shear it off will probably snap something. Same goes for machining the plate off, except
maybe by grinding. And when heated past a certain temperature—like if you tried to torch the glue off, or if you let it get too hot while grinding—they'll demagnetize. Then, even if you get it off, you'll probably lose the plating, meaning the magnet will corrode. And did I mention that magnetic dust is pretty hazardous (both because it's magnetic and will stick to things, and because it's chemically toxic when ingested).
But while I'm on the topic, remember that ferrous metals can be turned into magnets. (Yes, I'm looking at you, Vex sheet metal!) Most magnets are made the same way—using a powerful electromagnet, and a sintered slug of randomly magnetized rare earth or ferrous alloy—so it's not an illegal process. And that theory works in mundane ways too: want to bet that the backing on your hard drive magnet is made from steel—a ferrous metal.
(This of course raises the question of whether FIRST meant to say "permanent magnet", or whether any magnetized substance—like in an operating electromagnet, or a slug of iron next to a permanent magnet—will do.)
*When I say "reasonable attempt at compliance", I mean that they read the rule, attempted to determine its meaning as written, came to a plausible conclusion given the rulebook (this is the key; clearly incorrect interpretations are worthless), and successfully executed a design that complies with that meaning. This is certainly not a validation of the idea that they should be passed for giving it a good effort, even if noncompliant.