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With apologies to the late Mitch Hedberg, always design your device to fail like an escalator, not an elevator. When an escalator fails, it becomes stairs. When
by noonespecial 9y ago
With apologies to the late Mitch Hedberg, always design your device to fail like an escalator, not an elevator. When an escalator fails, it becomes stairs. When an elevator fails, it becomes jail.
Don't design a computer that is a smoke detector, design a smoke detector that happens to also have a computer. A kernel panic or complete loss of computing should leave behind a traditional smoke detector in a fancy looking case.
- ghaff 9y agoI agree (of course). It's even a bigger problem for me with the Nest thermostat. Living somewhere that gets cold in the winter I absolutely won't tolerate an added failure mode in my heating system. And I have other ways to monitor temperature that happen out-of-band of my furnace control.
- DougWebb 9y agoA couple of years ago I had a 'failure mode' problem with my heating system. A winter storm knocked out power in my area. My heating system was a natural-gas-fired boiler that produced steam, which thanks to gravity would rise up through my radiators, condense to water, and flow back to the boiler. The power outage didn't stop the gas, so the only thing that kept my furnace from running was the electric thermostat that sent on/off signals to the electric device that controlled the gas valve and sparked an ignitor. The thermostat itself had a battery backup, so it was trying to turn the heat on as my house cooled off. But the controller and ignitor had no backup. I couldn't even use a match to light the thing manually, because there was no way to open the gas valve. I understand the safety implications of adding a manual valve and spark ignitor to a furnace, but letting my pipes freeze (and me too) also has safety implications. Besides, there's probably already a thermo-mechanical safety mechanism that would slam the valve shut if the furnace gets too hot. Luckily, the power came back on in a few days, before my house got colder than light-jacket conditions. No frozen pipes.
- tgtweak 9y agoUnfortunately the ones that were immune to this employed Mercury switches, which I don't believe are sold any more. We had an older gas heating stove which had this and worked even when the electricity was out (particularly good in the winter when heating with electricity). Eventually that part failed and being an older model, that part was discontinued by the manufacturer. This forced us to get a "new" stove which now uses an electrical system to control it, and which doesn't have a battery backup integrated. Technically one could add a UPS, but since it also uses an electrical fan it would probably empty that ups within a few hours.
- thescriptkiddie 9y agoI don't know if these are available for boilers, but many natural-gas-fired water heater controllers are powered by a peltier device, which is heated by a small pilot flame.
- bjelkeman-again 9y agoI have an electric heatpump for heating and hot water. The first thing I did when moving in to the house was install a reasonably efficient, manual wood burning stove, with 2 m3 of wood in the basement. I have had the heat pump fail in the middle of the winter, but the wood burning avoided any freezing disaster.
- ghaff 9y agoOf course, that assumes you're at home. I added a wood stove (in addition to a fireplace that I already had) partly as a backup. But I also travel a fair bit.
- ihattendorf 9y agoAny reason you didn't have a backup generator? I would think if you were at risk of frozen pipes without electricity, it would be a wise investment.
- ghaff 9y agoThat's the situation for pretty much everyone in northern states. A generator that's wired in with propane tanks is a pretty significant expense and I'm still not sure how reliable it all is if no one is at home.
- soneil 9y agoIf the control line for your furnace is just a 24V loop (or a dry loop), a good hint is that you can keep a traditional thermostat in parallel with your 'smart" one - so that if either closes the loop, the furnace fires. Then you can aim for "comfortable" with your "smart" one and "safe" with your real one.
- ghaff 9y agoThat's probably true. And should also be part of the "smart" thermostat's design.
- sixothree 9y agoA nest failure in brutal New Orleans heat while I am out for a few days might spell death for one of my cats. I don't feel like Google takes their products seriously enough to trust them with the life of my pets.
- adrianratnapala 9y agoThis is a good point, but if I had pets, I don't think I would trust any air condition system at all to keep them alive for a few days. But then I don't really know what it's like to own pets, and I don't know how housing in New Orleans works either.
- PaulHoule 9y agoEscalators have bad failure modes too. An escalator can function as stairs because it has a set of brakes. If those brakes fail, gravity will send everyone on the belt into a high speed collision with the floor.
- marcuslager 9y agoThere has to be way to much friction in the mechanics for that to happen. No? Mitch. One of the greats. Uncopyable.
- pzenger 9y agoNope - Elevator failure in Hong Kong https://www.youtube.com/watch?v=ADb57ysvCbU https://www.youtube.com/watch?v=ADb57ysvCbU
- peller 9y agoDo escalators not come with a ratcheting mechanism to prevent exactly that from happening? Seems to me like a serious design error if not..
- euyyn 9y agoI guess they were designed to run in both directions, meaning you can't mechanically lock the "down" direction.
- FussyZeus 9y agoI mean, it's probably a Chinese escalator. We didn't get the term "Shenzhen Quality" out of thin air.
- StavrosK 9y agoThat seems a bit of a misnomer when everything is made in Shenzen.
- dechov 9y agoAs an exercise of the limits of this advice, how does this apply to designing elevators, short of "never design elevators"?
- ouid 9y agohard brakes that apply when doors are opened manually, and an emergency panel behind which a small ladder is located.
- jack9 9y agoThe costing difference between an elevator and stairs is substantial. Especially when you have to have stairs when you get an elevator by building code.
- bubblethink 9y agoBy having a manual fail safe that operates mechanically. i.e., without power.
- deleted 9y ago[deleted]
- OJFord 9y agoControlled descent to the next (lowest) floor, at which the properly aligned doors can be manually opened.
- squarefoot 9y agoI wonder how modern cars assisted steering and brakes fail when they do.
- catbird 9y agoYou can still steer and stop a car w/out power. It just takes a lot more force than you're used to.
- avisser 9y agoAlso, in an ICE car, the pump that pressurizes the power steering/breaking system is directly powered by belts off the engine. It's not electric and a computer does not mediate the power transfer. Which really makes me think what happens in a Tesla when the computer shits the bed...