Invisible <voi### [at] devnull> wrote:
> On 07/06/2011 07:49 PM, Aydan wrote:
>
> > As for precision, try the following experiment:
> > 1. Sit in front of your computer and put your finger on a key.
> > 2. Close your eyes
> > 3. wave aroud wildly with your arms
> > 4. put the finger back on the key from step one.
> > 5. open your eyes
> > Did you hit the same key? I doubt it.
>
> News flash: Robots can't do this either.

They absolutely can. Have a look at industrial robots

> For example, a hard drive has a "servo track" recorded on one platter,
> so that the read/write heads can sense where they are, since the voice
> coils that steer the heads can't reliably return to the same location
> with the necessary precision.

That's not a robot

> This, even though those voice coils are controlled by a normal computer,
> which is capable of doing perfectly "precise" calculations.
>
> This has nothing to do with the precision of the calculations that the
> controller performs, be it a computer or a brain. It's just an inherent
> result of mechanical devices being imprecise.

You should not conclude the precision of all possible drive mechanisms from the
precision if a single one.
HDD head positioning is done gearless. This is inherently imprecise.
They did it like that to be fast, reliable (no worn gears), and they knew they
can get the feedbak they need for accuracy.
Industrial robots for example have geared drives and you can have them move from
one positio to another and back to the exact same position without needing
external calibration. This is because they use stepper motors and geared drives
with very little play for exact reproducability of positions.
You can have one of those move for hours and it won't drift.
And it doesn't get feedback if it's still on track either.

> > If you can do that than that's what I'd call precice.
> > Moving your finger a few centimeters without watching and hitting a key that is
> > more than a finger wide is not precise.
>
> You don't play a musical instrument, do you?

No, but in this case it doesn't matter.

> Let me tell you, the black keys are *narrower* than a human finger. And
> if you're not careful, your fingers slip off the side. Doesn't sound
> very nice...

That may be, but does it really matter if you are a  millimeter off?
And let's say you move your hand about 10 cm and can hit a key within a
millimeter. Sounds realistic? That's still only 1% accuracy.
Your printer head for example can do much better. It can position to a fraction
of a millimeter over 20cm. Multiple times. Without recalibrating.
CNC machines can position to less than a tenth of a millimeter over several
meters. They don't get feedback either. They calibrate onec before starting a
process and run through the process without the need to recalibrate.

> Anyway, if that fails to convince you, try throwing a ball through a
> hoop. By the time you get any feedback about whether you hit or not,
> it's far too late to do anything about it; you've already let go of the
> ball! And yet, many people manage to throw precisely enough to do this
> reliably.

Precisely enough? Right.

Even the absolute pros won't be able to hit the hoop all the time exactly in the
center without touching the rim.
Sinking the ball has a much higher probability, because , up to a point it
doesn't matter if you hit the rim, it will still go in.
A basketball has a diameter of about 24cm the hoop has a diameter of about 45cm.
That makes 10 cm of error margin right there.
Let's say you need to hit the hoop within a radius of 15cm from a distance of
say 5 meters.
That's a whopping 3% of accuracy.
Even if you go out to 15m distance youl only be at 1% accuracy.
Not what I'd call accurate in robot terms.
Program a robot to throw the ball and you'll get better precision once you have
it calibrated properly.
That's the big difference: A human can quite confidently throw a ballinto a hoop
from a multitude of positions without much "setup" time.
But once a robot is calibrated to it's position it can hit the target forever.
The human usually can't.

> Similar story for anyone who plays darts, snooker, tennis, ...

OK, next time you are in a Pub with a darts board, have a look at the
"professionals" and how often they actually hit the triple 20 if they want to.

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