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

[Johnny Billquist]

On 2016-02-14 23:10, Scott Dorsey wrote:
> Johnny Billquist  <bqt at softjar.se> 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.
>
> Look at the nameplate on a typical induction motor, you will see that it
> is probably rated for around 2% slip.  A fan motor will have much higher.
> A synchronous motor won't have any.
>
> Because of that, a synchronous motor has an additional winding (or set
> of windings) in order to get it up to speed, or else it needs to be
> spun up by a second motor or a hand crank.
>
> If you watch Cinema Paradiso, for instance, the projectionist is using
> a Prevost projector with a synchronous motor and no start winding.  On
> the first film cue, he pushes in a crank, spins the motor up, turns the
> motor on so it can lock in on speed, then waits for the second film cue
> which is spaced long enough for the motor to be at speed and hits the
> douser to change over to the projector.

So we are down to a separate starter motor? Fair enough, if you have 
that then yes, you can definitely do different tricks. But then you no 
longer have that simple AC motor.

And I can tell you that the RP06 have no such thing. There is just one 
electric motor, and it's a DC one.

	Johnny

-- 
Johnny Billquist                  || "I'm on a bus
                                   ||  on a psychedelic trip
email: bqt at softjar.se             ||  Reading murder books
pdp is alive!                     ||  tryin' to stay hip" - B. Idol