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Never trust a system that seems to be working

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Re: Never trust a system that seems to be working

#121

Post by deepspace »

lisper wrote: post #84
adrian_b wrote: post #72

Earlier quoted context omitted.

This happens because the real insulators are better approximations of ideal insulators, than real conductors are approximations of ideal conductors. In electrical circuits made with normal conductors and insulators, e.g. copper wires and organic polymer insulators, it is possible to ignore the currents that branch from the wires and close through the insulators, because they are extremely small (e.g. in the femtoampe…

I have a bachelors degree in electrical engineering and work experience in hardware design and in the back of my mind I've always known this to be true, but this is the first time in my life I've ever heard anyone say this explicitly. EE pedagogy is badly broken in places.

As another EE, I had the opposite experience. Voltage drops due to wire resistance and transmission losses were drilled into our heads at any possible opportunity.

Re: Never trust a system that seems to be working

#122

Post by JoshTriplett »

macintux wrote: post #110
csours wrote: post #79

Earlier quoted context omitted.

"Read the error message, no wait don't close that go back" when helping people is a definite feeling. Take a deep breath. Take off your headset. Go outside. Never look at a computer again. Start driving a bulldozer. Life is good.

I’ve lamented here before, but the number of technical people who absolutely freeze up at the sight of an error message is daunting. Being able to interpret errors correctly is a huge step up in this industry; to me it feels like table stakes, but clearly isn’t.

> I’ve lamented here before, but the number of technical people who absolutely freeze up at the sight of an error message is daunting.

"freeze" is still a much better reaction than "quickly dismiss without paying attention". I can understand "freeze"; it's possible to learn and train from there to "good, well done, now read everything and think". I do not understand "quickly dismiss without reading and paying attention".

(I know about the studies for "people dismiss something that isn't getting them their goal", but I still don't understand the mindset that can dismiss something like that even when theoretically trying to figure something out.)

Re: Never trust a system that seems to be working

#123

Post by deepspace »

freedomben wrote: post #102
lisper wrote: post #84

Earlier quoted context omitted.

I have a bachelors degree in electrical engineering and work experience in hardware design and in the back of my mind I've always known this to be true, but this is the first time in my life I've ever heard anyone say this explicitly. EE pedagogy is badly broken in places.

Indeed, when discussing theory we love pretending that there's no voltage drop from the wires, which can really bite you when you get into design or deep failure analysis. All good technicians and engineers learn this reality fairly soon, and it's one of the things we check especially when dealing with indeterminate failures. As much as I love academia, I really wish there were more instructors with real experience t…

Maybe it has to do with the culture at specific schools. As I mentioned in another comment, my instructors loved to include wire resistance in their problems, and always explicitly stated the zero-loss assumption when applicable.

We did have a healthy incubation program, where instructors helped companies with product development, so perhaps that is what brought the real-world experience.

Re: Never trust a system that seems to be working

#124

Post by fknorangesite »

stewx wrote: post #116
hedora wrote: post #61

Earlier quoted context omitted.

It is also why white traffic lights no longer mean "go". White means "the red glass lens in front of the incandescent bulb shattered again". Related, from train signals: > The invention of the track circuit in 1872 by William Robinson permitted automatic block signals. Most simply, a low voltage battery current runs up one rail and down the other. As long as current flows from the battery through one rail to the rela…

We have white traffic lights now in Canada for "transit advance", when buses are allowed to proceed before the rest of traffic.

Yes but it's also a different symbol - a vertical line rather than the full circle (at least in my experience).

Re: Never trust a system that seems to be working

#125

Post by nordsieck »

bombcar wrote: post #111
acdha wrote: post #100

Earlier quoted context omitted.

Train air brakes are similar in failing safely for the same written-in-blood reasons: https://en.wikipedia.org/wiki/Railway_air_brake

Some military trucks are designed the opposite way on purpose - because they’d rather have no brakes and be able to move than be stuck on the battlefield.

> Some military trucks are designed the opposite way on purpose - because they’d rather have no brakes and be able to move than be stuck on the battlefield.

Do you have any details on that? Or a source I could read? I'm pretty curious now.

I drove trucks in the military - specifically, FMTV, HEMTT, HMMWV, and 5 tons. None of them had the reverse brakes you describe.

Re: Never trust a system that seems to be working

#127

Post by bombcar »

acdha wrote: post #120
bombcar wrote: post #111

Earlier quoted context omitted.

Some military trucks are designed the opposite way on purpose - because they’d rather have no brakes and be able to move than be stuck on the battlefield.

That’s a great example of how you always have to design for a context.

Yeah, any design is going to be various trade-offs, and you have to understand them (and how they may relate to your mission) when determining what to do and what would be a bad decision.

For example, cars have "fail open" brakes but have independent cylinders so that it is relatively hard to have all four wheels fail at the same time (older cars had single master cylinders) - and one of the tradeoffs is that people want cars to get going immediately and not wait for brake cylinders to "charge up".

As more and more things get computerized, you have more options for "intelligent failover" - anyone who used to drive an old manual car knew you could slow down using the engine - but now the computer could detect brake failure and do things for you to help recover.

And as seen from other comments, the modern US military prioritizes "on-road safety" over "under ongoing attack ability" - partially because of changing strategies I suspect, but also from the realization that the US military kills more members of the US military each year via accidents, etc, than anything else.

Re: Never trust a system that seems to be working

#128

Post by malloci »

usrbinenv wrote: post #88

A bit of an off-topic: I only ever saw white traffic lights in the US and Canada (specifically, pedestrian traffic lights) and they confused me a lot at first - the rest of the world uses green. The icons displayed (hands) are confusing too: the rest of the world uses an icon of a man walking or standing.

The hand is to mimic that of a traffic cop. When they want you to stop, they hold up their hand to indicate that you need to stop.

It used to be that you had to know english in order to understand them as well...many of the signs used to use the words "walk" and "don't walk"

Re: Never trust a system that seems to be working

#129

Post by bombcar »

nordsieck wrote: post #125
bombcar wrote: post #111

Earlier quoted context omitted.

Some military trucks are designed the opposite way on purpose - because they’d rather have no brakes and be able to move than be stuck on the battlefield.

> Some military trucks are designed the opposite way on purpose - because they’d rather have no brakes and be able to move than be stuck on the battlefield. Do you have any details on that? Or a source I could read? I'm pretty curious now. I drove trucks in the military - specifically, FMTV, HEMTT, HMMWV, and 5 tons. None of them had the reverse brakes you describe.

The deuce/half air-over-hydraulic brakes fail open (loss of air pressure leaves you with hydraulic brakes alone, loss of hydraulic leaves you with no brakes at all). However, there is a failure mode that leaves the brakes full on if the air cylinder jams.

At the time it was an acceptable trade-off; later military vehicles have more in common with trucks than tanks, I suspect.

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