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> How long does it take to do a computer simulation to check that something
> won't break? How complicated is the process, and how much computer time
> does it take?
That sort of simulation is very quick and easy, only a few hours for a
moderately complicated part and then you get back data about the stress at
every point.
The harder simulations are the ones where you want to actually simulate some
dynamic force (like your product being dropped on the floor) and then of
course the simulator needs to deal with collisions and deformations. These
sorts of simulations can take a long time to set up and run for days just to
simulate a fraction of a second.
> So... corrugated? Or something.
On the one I worked on we just bolted the base of the display to the car,
and then had two hooks at the back half way up that hooked into the car
mechanics (no screws). That way when you pulled forward on the display the
hooks provided the strength and stiffness, and if you pushed back the hooks
did nothing so you were free to bend the bottom fixing points if you hit it
hard enough.
> Heh, yeah. I guess if you've made something similar before it helps a lot.
> ;-) I was just thinking, I imagine for "most" manufactured items, the
> designers probably have a basic intuition about roughly what thickness of
> metal is required. I don't suppose they do an exhaustive mathematical
> derrivation of optimal thickness for every single component ever designed.
It depends on the product and how critical it is, plus how many you are
making. For something you are only making 1 of, like a bridge or a big
building, you will probably do a lot of calculations. If you are planning
to make 10 million of something, you can probably just make a few hundred
test samples and have chance to optmise them if needed.
> Right. So you take an educated guess, and if the prototypes fall apart,
> you figure out which bit broke?
Yup, for car parts we usually have 3 rounds of prototypes before mass
production starts.
> Almost every platform known to man already has a C compiler - even if it
> has nothing else. The C compiler is typically the very first thing that
> gets built. ;-)
Someone still has to build it though in the first place.
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>> How long does it take to do a computer simulation to check that
>> something won't break? How complicated is the process, and how much
>> computer time does it take?
>
> That sort of simulation is very quick and easy, only a few hours for a
> moderately complicated part and then you get back data about the stress
> at every point.
Right. So not instantaneous, but not months of computer time either.
I take it there's more to it then just asking the computer "hey, will
this break if I put 25 N through it?"
> The harder simulations are the ones where you want to actually simulate
> some dynamic force (like your product being dropped on the floor) and
> then of course the simulator needs to deal with collisions and
> deformations. These sorts of simulations can take a long time to set up
> and run for days just to simulate a fraction of a second.
At what point does it become cheaper to just make the thing rather than
simulate it?
>> So... corrugated? Or something.
>
> On the one I worked on we just bolted the base of the display to the
> car, and then had two hooks at the back half way up that hooked into the
> car mechanics (no screws). That way when you pulled forward on the
> display the hooks provided the strength and stiffness, and if you pushed
> back the hooks did nothing so you were free to bend the bottom fixing
> points if you hit it hard enough.
Mmm, ingenious.
> It depends on the product and how critical it is, plus how many you are
> making. For something you are only making 1 of, like a bridge or a big
> building, you will probably do a lot of calculations. If you are
> planning to make 10 million of something, you can probably just make a
> few hundred test samples and have chance to optmise them if needed.
Well yeah, it's going to depend on how safety-critical it is. If you're
making a coathanger, probably not much need to test it. If you're making
a karabina... there are probably legal requirements for exhaustive testing.
>> Right. So you take an educated guess, and if the prototypes fall
>> apart, you figure out which bit broke?
>
> Yup, for car parts we usually have 3 rounds of prototypes before mass
> production starts.
One thing I always wondered... You see people doing all these crash
tests, right? So... where the hell do you get an endless supply of red
cars to crash into things?!
>> Almost every platform known to man already has a C compiler - even if
>> it has nothing else. The C compiler is typically the very first thing
>> that gets built. ;-)
>
> Someone still has to build it though in the first place.
Sure. But not the Haskell development team. ;-)
I would think it's by a cross-compiler though, yes. Indeed, some systems
are "too small" to run a C compiler natively, so you *must* cross-compile.
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Invisible wrote:
> myself. OTOH, I have yet to write a working Tic-Tac-Toe program, so...
> maybe not. :-/
I did that in grade school. :) It was unbeatable.
--
~Mike
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>> myself. OTOH, I have yet to write a working Tic-Tac-Toe program, so...
>> maybe not. :-/
>
> I did that in grade school. :) It was unbeatable.
The hard part is figuring out how to draw the graphics on screen and
register the mouse clicks. Usually you have to mutilate your program to
fit the window manager's event loop...
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> The hard part is figuring out how to draw the graphics on screen
Choose a language / IDE / API that gives you easy access to graphics?
> and register the mouse clicks.
Ditto.
> Usually you have to mutilate your program to fit the window manager's
> event loop...
Don't see how, if you have written functions like:
MouseClicked(int xpixel , int ypixel)
RedrawScreen()
etc, you just need to call them in response to the correct window manager
messages. Of course if you write the whole game as just a big long chunk of
code you are going to find it hard to fit it in with a window manager.
BTW why don't you just do a text based version?
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> I take it there's more to it then just asking the computer "hey, will this
> break if I put 25 N through it?"
Not much more, just specify which parts are fixed (eg mounting brackets) and
then tell it which surfaces to apply a force to. It will then run some sort
of iteration algorithm until it has "solved" the structure so that all
internal forces are perfectly balanced. Then you can just ask it for the
maximum stress in the structure and see how big it is compared with the
yield stress of the material...
> At what point does it become cheaper to just make the thing rather than
> simulate it?
Hmm, the first samples are always quite expensive to make because you are
making so few of them, but usually it's more a time thing than money. It
can take 2 or 3 months from finalising the design until you have assembled
samples in your hands, and of course the customer usually has a deadline for
releasing the product so you can't just carry on making more and more
samples until you get it right. If you know something is critical to get
right and you haven't done it much before, then you simulate it.
> Mmm, ingenious.
Similar to how your steering wheel is connected to the wheels by a
telescopic tube, so in the event of an accident the telescopic bits collapse
rather than the rod coming through the front of the steering wheel and into
your chest! Although Jeremy Clarkson would say that would make people drive
safer...
> Well yeah, it's going to depend on how safety-critical it is. If you're
> making a coathanger, probably not much need to test it. If you're making a
> karabina... there are probably legal requirements for exhaustive testing.
Well yes, and then you get things inbetween, like the wrist strap for the
Wii remote control, where for some reason they didn't realise it would snap
if you pulled it hard. I mean WTF how can you miss that one? I would have
thought they would have got some really strong guy to throw it around while
measuring the force, and then made sure it could withstand double or
something. Maybe Japanese "strong guys" are not that strong :-)
> One thing I always wondered... You see people doing all these crash tests,
> right? So... where the hell do you get an endless supply of red cars to
> crash into things?!
A car factory? They make lots of prototypes too for many different
purposes, btw I don't think they have to crash very many to pass the
official tests, maybe even only 1 car, IDK.
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>> I take it there's more to it then just asking the computer "hey, will
>> this break if I put 25 N through it?"
>
> Not much more
Mmm, OK.
> just specify which parts are fixed (eg mounting brackets)
> and then tell it which surfaces to apply a force to. It will then run
> some sort of iteration algorithm until it has "solved" the structure so
> that all internal forces are perfectly balanced. Then you can just ask
> it for the maximum stress in the structure and see how big it is
> compared with the yield stress of the material...
I guess like you say, working out whether a component will snap under a
given load is much easier than determining (say) whether a car engine
will explode when you ignite petrol vapour inside it.
>> At what point does it become cheaper to just make the thing rather
>> than simulate it?
>
> Hmm, the first samples are always quite expensive to make because you
> are making so few of them, but usually it's more a time thing than
> money.
Ah, but time *is* money, because...
> of course the customer usually has a deadline for releasing the product
Even so, I'm kinda surprised at the lead-time for a prototype. Mind you,
I guess if you just want to build a model of something, that's quite
easy. If you want to build it out of the real materials for strength
test purposes, that's a tad slower...
> If you know
> something is critical to get right and you haven't done it much before,
> then you simulate it.
OK.
> Similar to how your steering wheel is connected to the wheels by a
> telescopic tube, so in the event of an accident the telescopic bits
> collapse rather than the rod coming through the front of the steering
> wheel and into your chest! Although Jeremy Clarkson would say that
> would make people drive safer...
LOL! Well, Clarkson is a moron. ;-)
> Well yes, and then you get things inbetween, like the wrist strap for
> the Wii remote control, where for some reason they didn't realise it
> would snap if you pulled it hard. I mean WTF how can you miss that
> one? I would have thought they would have got some really strong guy to
> throw it around while measuring the force, and then made sure it could
> withstand double or something. Maybe Japanese "strong guys" are not
> that strong :-)
Hehehe. Apparently the world record for the loudest human shout is held
my somebody from Japan or China. They're pretty crazy people, really.
Not sure how strong though...
>> One thing I always wondered... You see people doing all these crash
>> tests, right? So... where the hell do you get an endless supply of red
>> cars to crash into things?!
>
> A car factory? They make lots of prototypes too for many different
> purposes, btw I don't think they have to crash very many to pass the
> official tests, maybe even only 1 car, IDK.
"And in this test, we're going to crash a new car into an 20-year old".
Uh, and where did you get that from, exactly?
Also, why do they already have to be painted random colours?
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Invisible <voi### [at] dev null> wrote:
> Even so, I'm kinda surprised at the lead-time for a prototype. Mind you,
> I guess if you just want to build a model of something, that's quite
> easy. If you want to build it out of the real materials for strength
> test purposes, that's a tad slower...
Even more so if you not only want to get the real material, but also the real
manufacturing process. It may make a hell of a difference, for instance,
whether you drill a hole or instead punch it. Planes have crashed due to such
details.
I guess machined parts are easy to prototype: Just feed the CAD data into a CAM
machine and wait a few moments, that's it (basically).
However, often you don't want your final product to be machined, because that's
prohibitively expensive for a lot of purposes. Pressed (is that the right
word?) or cast parts or the like are much different: They need special tools
that need to be made first (e.g., the molds in case of cast parts). Again,
they're prototypes.
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> I guess like you say, working out whether a component will snap under a
> given load is much easier than determining (say) whether a car engine will
> explode when you ignite petrol vapour inside it.
Yes, in fact some calculations you can even do by hand without simulation
just by using elementary beam bending mechanics.
> Even so, I'm kinda surprised at the lead-time for a prototype. Mind you, I
> guess if you just want to build a model of something, that's quite easy.
> If you want to build it out of the real materials for strength test
> purposes, that's a tad slower...
I did have a break down of the lead time somewhere, but there are mechanical
parts, optical parts, electrical parts, which all have to be designed in
complete detail and work together (your electrical engineer can't say he
needs a PCB that is bigger than the mechanical housing, and his circuit
needs to give the correct voltages to the LCD etc etc), then the tool-maker
must take those designs and design and build his tools, then the tools have
to be approved and tested to make sure they are making parts with the
correct accuracy, then finally the individual parts can be made (perhaps 500
pieces for a typical prototype run), and then they are assembled. For the
later prototype stages they have to actually be made using the same
equipment that will be used for mass production, so the whole assembly line
needs to be set up and checked etc.
> "And in this test, we're going to crash a new car into an 20-year old".
> Uh, and where did you get that from, exactly?
I think the crash test standards give quite detailed information about what
you have to crash into. All those crash test dummies you see are made to
exact specifications that simulate eg the 95th percentile of human
proportions and weights.
> Also, why do they already have to be painted random colours?
I don't think the colour matters too much, but they usually have all those
circular stickers on them divided into 4 for the software to easily measure
the movement and distortion of the car from the video sequence.
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scott wrote:
>> I guess like you say, working out whether a component will snap under
>> a given load is much easier than determining (say) whether a car
>> engine will explode when you ignite petrol vapour inside it.
>
> Yes, in fact some calculations you can even do by hand without
> simulation just by using elementary beam bending mechanics.
Heh. Rather you than me! ;-)
> I did have a break down of the lead time somewhere, but there are
> mechanical parts, optical parts, electrical parts, which all have to be
> designed in complete detail and work together (your electrical engineer
> can't say he needs a PCB that is bigger than the mechanical housing, and
> his circuit needs to give the correct voltages to the LCD etc etc), then
> the tool-maker must take those designs and design and build his tools,
> then the tools have to be approved and tested to make sure they are
> making parts with the correct accuracy, then finally the individual
> parts can be made (perhaps 500 pieces for a typical prototype run), and
> then they are assembled. For the later prototype stages they have to
> actually be made using the same equipment that will be used for mass
> production, so the whole assembly line needs to be set up and checked etc.
Makes you start wondering how anything ever gets made at all...
>> "And in this test, we're going to crash a new car into an 20-year
>> old". Uh, and where did you get that from, exactly?
>
> I think the crash test standards give quite detailed information about
> what you have to crash into. All those crash test dummies you see are
> made to exact specifications that simulate eg the 95th percentile of
> human proportions and weights.
...20-year old *car*. :-P
>> Also, why do they already have to be painted random colours?
>
> I don't think the colour matters too much, but they usually have all
> those circular stickers on them divided into 4 for the software to
> easily measure the movement and distortion of the car from the video
> sequence.
Oh, is *that* what those are for??
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