What drives the main motor of a hard disk drive? Is it a constant DC
voltage, or is there some more complex control?
And for the arm that moves the heads, actuated via a voice coil, what
sort of input does the voice coil receive?
We used to understand the technolgy around us - or could study it and
replicate it. Now the knowledge and ability is with so few.
I could understand a steam engine well enough to design a fundemental one.
I could not design say a memory chip!
On 15/05/17 14:36, email@example.com wrote:
"Earliest speeds of rotation varied widely, but by 1910 most records
were recorded at about 78 to 80 rpm. In 1925, 78.26 rpm was chosen as a
standard for motorized phonographs, because it was suitable for most
existing records, and was easily achieved using a standard 3600-rpm
motor and 46-tooth gear (78.26 = 3600/46)"
Of course that was America, where 60hz was the norm, here at 50hz you
get 3000rpm motors
And of course ratios using exact ratios of gears are deprecated because
of uneven gear wear, so we can throw that one out of the box.
It may be that there was some sort of motor/gear assembly that produced
about 78 rpm, and that this got to be 'the standard' but there is no
real reason for any turntable speed to be a standard.
Any more than 4' 8 1/2" is the ideal railway gauge.
There is something fascinating about science. One gets such wholesale
returns of conjecture out of such a trifling investment of fact.
Of course not, there was no existing standard. Someone just picked a
horse drawn cart at random, measured the distance between the wheels and
said "that's how far apart we'll make the rails'. From then onward all
wagons that were to run on the rails had to have the wheels that far
apart. There was no previous standard for the distance between the
wheels of horse drawn carts, if they'd picked a different cart in the
shed the track width would have been different.
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