[Info-vax] OT: the Daily WTF for today is a VAX/VMS story

[johnwallace4 at yahoo.co.uk]

On Monday, 15 February 2016 19:24:44 UTC, Chris  wrote:
> On 02/14/16 19:58, Johnny Billquist wrote:
> > On 2016-02-14 14:31, Scott Dorsey wrote:
> >> Johnny Billquist <bqt at softjar.se> wrote:
> >>> However, no hard drive uses a 3-phase AC motor to drive the disk. Anyone
> >>> with half a brain should realize this. 3 phase AC motors always follows
> >>> the phases of the supply like slaves. There is no spinup time. You go
> >>> from standstill to full speed immediately, always. That is not how you
> >>> want to spin up a disk drive.
> >>
> >> If the motor is designed to have some slip, you can bring it up to speed
> >> without too much trouble. Synchronous motors in general always follow
> >> the supply like slaves, no matter how many phases they have.
> >
> > "Slip"? An AC motor cannot have slip. It is controlled by the phases of
> > power. It has to follow the phases.
> >
> 
> Sorry, but that's incorrect. Ac squirrel cage induction motors,
> single or multiphase, have slip which varies with load. The only
> exception is synchronous ac motors, which are used where constant
> speed is required. They do tend to be less powerful than similarly
> sized induction motors though. First year electrical eng stuff
> really.
> 
>  From memory, many dec drives (R80, RA**) used induction ac motors for
> spindle power, (they are cheap and reliable) but may have had
> thyristor or other solid state control to stabilise the speed. RLxx 
> series also used ac motors. Most vendors would try to avoid any
> motor design with brushes, as they are very electrically noisy and
> are not very reliable...
> 
> Regards
> 
> Chris

Not necessarily even first year electrical engineering; there's a
handy and reasonable looking quick reference on induction motors
in Wikipedia:
https://en.wikipedia.org/wiki/Induction_motor
(well, reasonable in comparison with some stuff recently written here).