Hard disk drive motors/actuators

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?
Thanks,
Daniele
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On 14/05/17 12:53, D.M. Procida wrote:

I beleive electricitry is involve4d
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On 14/05/2017 12:53, D.M. Procida wrote:

They are brushless DC motors, what else do you think Dyson copied?

Analogue servo controlled by digital controller, may be PCM but I haven't been involved or interested in the internals of HDD since they had stepper motors.
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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!
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wrote:

Yes, NASA figured that an alien civilisation might be able to play a gramophone record, but could they play a CD?
--

Graham.
%Profound_observation%
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Given we've not managed to travel to another inhabited planet, I'd say it would be fair to assume any aliens who managed to get here would likely be rather more advanced than us?
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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...but could have taken an alternative route in technology.
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If so, why assume a 'gramaphone record' would be obvious to them?
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*I wonder how much deeper the ocean would be without sponges*

Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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Because 45rpm is so logical!
It is between 33 and 78
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"DerbyBorn" wrote in message

16 2/3 rpm actually. LP at half speed.
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;-)
I did once find the explanation why the original tape speed was 30 ips - but never why 78 rpm was chosen for records.
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Dave Plowman snipped-for-privacy@davenoise.co.uk London SW
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On Monday, 15 May 2017 14:30:38 UTC+1, Dave Plowman (News) wrote:

IIRC it was originally 80rpm, with early recordings being inconsistent on speed. I suspect 78 was just somewhere among what we've already got.
NT
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On 15/05/17 14:36, snipped-for-privacy@gmail.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)"
https://www.library.yale.edu/cataloging/music/historyof78rpms.htm
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.
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The Natural Philosopher wrote:

Does not even convert to metric evenly
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On 16/05/2017 07:10, FMurtz wrote:

[snip]

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.
--
Mike Clarke

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On Tue, 16 May 2017 11:35:14 +0100, Mike Clarke

I think Network Rail still measures distances in chains.
--

Graham.
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"Dave Plowman (News)" wrote in message wrote:

Not here, moron. NASA sent it out there.
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On Sunday, 14 May 2017 15:24:00 UTC+1, Dave Plowman (News) wrote:

It can be shown statistically that there is no complex life elsewhere in the universe.
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On Monday, 15 May 2017 17:38:47 UTC+1, harry wrote:

quite the contrary - though we've never found any evidence of it existing.
NT
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"harry" wrote in message London SW

Show me.
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