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Comment by Brian_K_White | Hacker News Reader

I'm not sure what the value is of a hunk of steel that can last forever, if it's wasting power that whole time, and needs to be rebuilt periodically anyway. In the end, all you save is not having to manufacture a couple of castings and a shaft again. Those aren't especially expensive materials or processes. And a lightweight motor is especially valuable in anything that moves.

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This is precisely why most people abandoned old appliances, even if they “last forever”. Often the energy efficiency of newer devices is well worth the reduced lifespan.

Also, survivorship bias. Not every electric motor made a century ago survived until today; we just see the really well made ones that did.

Really well made or really well designed? Even a century ago, there wouldn't be that much variation between one motor and the next on a given production line.

Made, not designed. Mass production a century ago was a fundamentally manual process, and therefore would show much more variation per item than modern processes.

The only argument for it being designed for durability is that the designers assumed poor tolerances in the manufacturing process, and therefore designed with that in mind.

  > The only argument for it being designed for durability is that the designers
  > assumed poor tolerances in the manufacturing process, and therefore designed with that in mind.

Another issue was uncertainty. A century ago we did not have such precise ideas of metal fatigue and other material failures as we have today. Witness the DeHavilland Comet for and extreme but well-known example. Today, the oft-maligned term "designed to fail" actually means that all parts of a device can fail at once, instead of over-building some parts at the expense of cost, weight, and efficiency.

That variation would account for some premature failures, not a few motors randomly lasting 100 years by exceptional luck and skill. 100 years is just the performance you get when the thing is assembled correctly.

The variation would occur on both sides of the bell curve. A few motors will die prematurely, and a few will last forever. The classical bathtub curve of failures will skew the bulk of the failures out past a decade or so, but on the order of a century only the lucky few exceptionally-built, or exceptionally-maintained devices will last.

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