Three robot arm specs that don't trade off the way you'd guess. Two of them interact through leverage. The third barely trades off against either.
Every industrial robot arm datasheet leads with three numbers: payload (how much it can carry), reach (how far it can carry it), and repeatability (how consistently it returns to the same taught position). They sound like three independent facts you can read off a spec sheet and combine freely. They aren't. Payload and reach are physically coupled through leverage at the base joints — quote a single payload number and you've implicitly quoted it at a specific reach. Repeatability, meanwhile, is almost entirely decoupled from both — and it is routinely confused with a fourth spec, absolute accuracy, that most repetitive industrial tasks don't actually depend on.