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Stephen wrote:
> The Romans pretty much had the same gods as the Greeks, the names were changed
> to protect the innocent. :)
Well, yes, naturally. All the more reason to start wars over it. ;-)
> Also when the Romans were in power Greece was subjective to them and I would
> think that they would talk about Jupiter or Jove rather than Zeus to Romans out
> of respect.
I wasn't sure that was the case. My ancient history isn't too good. :-)
--
Darren New / San Diego, CA, USA (PST)
Helpful housekeeping hints:
Check your feather pillows for holes
before putting them in the washing machine.
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>> Exactly, which is why they should have systems in place to stop mistakes,
>> which will happen, getting outside their company. But I guess that costs
>> money so they make some compromise.
>>
>
> Those systems are made by humans, so they are always compromises.
Of course, but a group of clever humans can design a system that prevents
all the common mistakes from getting out.
> Or why do you think software has bugs and holes? :)
Because usually it's not worth the effort preventing them getting out? It's
not because it's impossible. Compare software released for home/office use
with software released for running cars, or factories, or power stations, or
planes, or space ships.
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And lo on Mon, 14 Jul 2008 17:18:06 +0100, Warp <war### [at] tag povrayorg> di
d
spake, saying:
> Phil Cook <phi### [at] nospamrocainfreeservecouk> wrote:
>> On that note I recall reading somewhere a suggestion that it's caused
by
>> us thinking in binary - If A = Good then !A = Bad; such that if w
e've
>> been
>> doing A a lot because we think it's good and it turns out not to be w
e
>> automatically turn to !A, because now that must be good :-)
>
> Actually we think in ternary. The third value is "I don't care", whi
ch
> sometimes also causes problems when taken to an extreme.
I don't think you'll find anyone who's that neutral.
To use my hypothetical hat-wearing law; there will be those who think it
's
bad and those who think it's good. It may be possible to argue that thos
e
who say "I don't care" have no strong feelings either way, but I would
expect a modifier such as "I don't care, but I think it's a bit stupid"
or
"I don't care, but it certainly makes everyone look smarter".
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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On Mon, 14 Jul 2008 11:20:31 -0700, Darren New <dne### [at] sanrrcom> wrote:
>Stephen wrote:
>> The Romans pretty much had the same gods as the Greeks, the names were changed
>> to protect the innocent. :)
>
>Well, yes, naturally. All the more reason to start wars over it. ;-)
>
A very good point.
>> Also when the Romans were in power Greece was subjective to them and I would
>> think that they would talk about Jupiter or Jove rather than Zeus to Romans out
>> of respect.
>
>I wasn't sure that was the case. My ancient history isn't too good. :-)
I guessed :-)
--
Regards
Stephen
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scott wrote:
>> Or why do you think software has bugs and holes? :)
>
> Because usually it's not worth the effort preventing them getting out?
> It's not because it's impossible. Compare software released for
> home/office use with software released for running cars, or factories,
> or power stations, or planes, or space ships.
>
You don't think there's bugs in these? ;) NASA's space shuttle is an
exception. I read an article somewhere that before any program change is
made, there are meetings upon meetings. I'm sure there are glitches in
the firmware of cars, you probably don't notice, or think its something
mechanically wrong.
I can tell you automated manufacturing equipment does, in fact, have
bugs. I've seen serious software errors in the FIRMWARE of servo
drives*. Some of which are used in such applications as airplanes. No
worries, though, most of the bugs can be worked around and the main PID
loop seems to do what its supposed to. Mostly. I've seen bearings in our
equipment crushed because a drive didn't stop pumping current into the
motor when it ran against a hard stop. Entertaining -- it ramped the
current up high enough to fry the motor coils. Oops. I've personally
stripped toothed belts bare because of a software error. Had I had the
blade running (I never do in testing, I always have the blade removed) I
would have run a saw blade into a steel I-Beam. I can't even imagine the
consequences for that. I don't think it would be pretty.
There's a reason equipment has a hard-wired emergency stop button that
cuts the power to the drives and motors.... Oh, and most avionics have
direct linkage to the controls. The drives AFAIK are only used in
autopilot, so that can be disengaged if something goes awry.
* For the curious: A servo drive is generally a signal generator and
amplifier used for driving a servo motor. The signal is controlled by a
feedback loop (PID - Andrew should know what this means, Proportional,
Integral, Derivative ) the general case is the greater the error, the
more current fed to the motor. As the error decreases, so too does the
current (P), the motor will eventually settle into position smoothly
(I,D). Thankfully, the heavy calculus lifting is done in the drive's
firmware all the software has to do is give it the factors found from
running a tuning routine, then feed it position, velocity or torque
(depending on your goals) It will then use the PID loop to achieve the
desired value. Obviously there are limits. The drive may allow a few
counts either way on position to be "in position" it may allow some
slack in velocity, or may allow some difference in applied torque. There
is of course a maximum current the motor can handle for short bursts. A
maximum amount of error for a certain amount of time the drive will
tolerate before it gives up, powers down the motor and reports a fault.
The drive described above didn't do this. The error was right below
maximum, but far enough to pump the full amount of current into the motor.
I've had some fun with servo drives in a "lab" setting. Usually the
motor will have a toothed wheel on it, so I can see what its doing. Once
the motor is in position, if the drive is still on, you can grab the
wheel and turn it, and depending on the tuning parameters it can have a
very soft feel, or hard feel. It reacts almost like a rubber band or a
spring. The more you turn it out of position, the more it fights you.
Even small motors have an amazing amount of torque. With low enough
current limits, you can turn the motor past the maximum position error,
and have it "break free" You can also grab it while its turning, hold it
and feel it stop trying once the error gets past a certain amount.
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>> Because usually it's not worth the effort preventing them getting out?
>> It's not because it's impossible. Compare software released for
>> home/office use with software released for running cars, or factories, or
>> power stations, or planes, or space ships.
>>
>
> You don't think there's bugs in these? ;)
Of course there are, but far less than in desktop software. My point was
that depending how much effort you want to put in to it, you either end up
with software like Microsoft, software like Nasa, or somewhere inbetween.
> I read an article somewhere that before any program change is made, there
> are meetings upon meetings.
I think that happens for a lot of software development, not just in space
shuttles.
> I'm sure there are glitches in the firmware of cars, you probably don't
> notice, or think its something mechanically wrong.
It's extremely unusual though, almost unheard of, for there to be any
noticeable glitch in the core software running a car. It's simply because
the consequences are so great, that the effort is put in to ensure that no
glitches ever can occur. Especially nowadays with all the stability, engine
and other control stuff run by software, it would be a total disaster for
any company if their cars suddenly did something stupid under certain
conditions.
> I've seen bearings in our equipment crushed because a drive didn't stop
> pumping current into the motor when it ran against a hard stop.
I saw a solid steel drive bar approx 10cm diameter sheared in two by a
motor, it was meant to be driving a machine to compress paper, but it got
jammed and for some reason the controller didn't stop the motor but kept
giving it more power.
> Entertaining -- it ramped the current up high enough to fry the motor
> coils. Oops. I've personally stripped toothed belts bare because of a
> software error.
But if you knew your software was to control something like a car or plane
with people in it, you would have course checked and tested your software
more thoroughly. That's my original point, ditto with Andrew's order, if
they really cared enough they would have systems in place to make sure that
incorrect orders could not be delivered.
> Oh, and most avionics have direct linkage to the controls. The drives
> AFAIK are only used in autopilot, so that can be disengaged if something
> goes awry.
Maybe on very small civilian aircraft, but on any passenger carrying jet or
military jet the control system is totally electronic with no mechanical
linkages. I suspect it would be near impossible for a person to manually
control most planes mechanically, both because of the high forces needed,
and the lack of an electronic controller to help keep things stable.
But usually there are 4 totally separate controllers, so they do have a high
degree of redundancy.
> Thankfully, the heavy calculus lifting is done in the drive's firmware all
> the software has to do is give it the factors found from running a tuning
> routine, then feed it position, velocity or torque (depending on your
> goals) It will then use the PID loop to achieve the desired value.
Reminds me of doing PID control loops at University, our lecturer had this
huge example about 2 metres high with a beefy motor controlling this mass on
cables around a pulley. He spent almost the whole lecture explaining the
theory (where most people had fallen asleep due to the horrendous calculus
involved), and at the end did the demo. He had set it up to get from point
A to point B in the shortest time with something like 5% overshoot.
Everyone was suddenly paying attention now as he was about to switch it on,
and then as he flicked the switch, the mass moved extremely quickly to point
B, past point B, kept accelerating and smashed off the end of the demo.
Everybody laughed.
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On Tue, 15 Jul 2008 07:36:10 -0500, Mike Raiford <mra### [at] hotmailcom> wrote:
>(PID - Andrew should know what this means, Proportional,
>Integral, Derivative )
Thank you I read it as "Piping & Instrumentation Diagram"
--
Regards
Stephen
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scott wrote:
> Of course there are, but far less than in desktop software. My point
> was that depending how much effort you want to put in to it, you either
> end up with software like Microsoft, software like Nasa, or somewhere
> inbetween.
NASA?
Aren't they those guys who tried to launch a rocket with a faulty O-ring?
Mmm, I guess it's not only M$ that sometimes rushes things due to
"launch shedules".
(You see what I did there?)
>> I'm sure there are glitches in the firmware of cars, you probably
>> don't notice, or think its something mechanically wrong.
>
> It's extremely unusual though, almost unheard of, for there to be any
> noticeable glitch in the core software running a car. It's simply
> because the consequences are so great, that the effort is put in to
> ensure that no glitches ever can occur. Especially nowadays with all
> the stability, engine and other control stuff run by software, it would
> be a total disaster for any company if their cars suddenly did something
> stupid under certain conditions.
Depends on how "stupid". I hear there's a car (I forget which) that has
a design fault so anybody who knows the "trick" can open the boot with
their bare hands even when it's locked - yet the manufacturers
repeatedly refused to admit that anything was wrong...
> I saw a solid steel drive bar approx 10cm diameter sheared in two by a
> motor, it was meant to be driving a machine to compress paper, but it
> got jammed and for some reason the controller didn't stop the motor but
> kept giving it more power.
I saw a machine that can casually snip through 30 mm spring steel the
way a hole punch cuts through tissue paper. The operator commented
"don't put your fingers in this". (!!)
> But if you knew your software was to control something like a car or
> plane with people in it, you would have course checked and tested your
> software more thoroughly. That's my original point, ditto with Andrew's
> order, if they really cared enough they would have systems in place to
> make sure that incorrect orders could not be delivered.
This is what it all comes down to. You can make things as reliable as
you want - it's merely a question of how much money you want to spend
doing it. ;-)
> But usually there are 4 totally separate controllers, so they do have a
> high degree of redundancy.
...I also saw a black-box flight recorder yesterday...
(It was orange.)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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Orchid XP v8 <voi### [at] devnull> wrote:
> NASA?
> Aren't they those guys who tried to launch a rocket with a faulty O-ring?
Take two programs of comparable size made in Microsoft and in NASA,
and compare the total amount of bugs found during testing. The former will
have in the order of thousands, while the latter will have something
like 10.
And the latter while never exceeding budgets nor deadlines.
--
- Warp
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scott wrote:
>> I read an article somewhere that before any program change is made,
>> there are meetings upon meetings.
>
> I think that happens for a lot of software development, not just in
> space shuttles.
>
Some, but definitely not all. Many places a small fix-up may not need a
day's worth of meetings, but with the shuttle, not a single line of code
can be changed.
I think this is the article:
http://findarticles.com/p/articles/mi_m0ISJ/is_n1_v33/ai_15103437
>> I'm sure there are glitches in the firmware of cars, you probably
>> don't notice, or think its something mechanically wrong.
>
> It's extremely unusual though, almost unheard of, for there to be any
> noticeable glitch in the core software running a car. It's simply
> because the consequences are so great, that the effort is put in to
> ensure that no glitches ever can occur. Especially nowadays with all
> the stability, engine and other control stuff run by software, it would
> be a total disaster for any company if their cars suddenly did something
> stupid under certain conditions.
I seem to remember a glitch in the ABS system for certain GM vehicles
many years ago.
>> Entertaining -- it ramped the current up high enough to fry the motor
>> coils. Oops. I've personally stripped toothed belts bare because of a
>> software error.
>
> But if you knew your software was to control something like a car or
> plane with people in it, you would have course checked and tested your
> software more thoroughly. That's my original point, ditto with Andrew's
> order, if they really cared enough they would have systems in place to
> make sure that incorrect orders could not be delivered.
In this case it didn't make it to production until it was corrected. We
really didn't want our customers to have to constantly replace bearings
and motors. ;)
>> Oh, and most avionics have direct linkage to the controls. The drives
>> AFAIK are only used in autopilot, so that can be disengaged if
>> something goes awry.
>
> Maybe on very small civilian aircraft, but on any passenger carrying jet
> or military jet the control system is totally electronic with no
> mechanical linkages. I suspect it would be near impossible for a person
> to manually control most planes mechanically, both because of the high
> forces needed, and the lack of an electronic controller to help keep
> things stable.
>
> But usually there are 4 totally separate controllers, so they do have a
> high degree of redundancy.
Ah, I figured the avionics linkages would be hydraulic, not computer
controlled.
> about to switch it on, and then as he flicked the switch, the mass moved
> extremely quickly to point B, past point B, kept accelerating and
> smashed off the end of the demo. Everybody laughed.
Heh. Ouch...
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