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PICList Thread
'[PIC]: frying eggs with a ULN2003 : my apologies'
2001\03\02@151715 by Joan Ilari

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Dear Piclisters

Some days ago I posted this email to the list :

{Quote hidden}

Many people have answered with different suggestions as you can
check by reviewing the thread. Many of these postings contained
interesting hints and suggestions of great value for me. I wish
to thank all of you for your help.

However, I must admit that I was TERRIBLY wrong because the motor
I was trying to control is NOT a stepper motor. Olin Lathtrop
friendly suggested this possibility :

== Do you have any evidence that this is not a brushless DC motor?  That
would
== be more likely if it turned the disk drive spindle.  If it moved the
heads
== then it is more likely a stepper.

Another piclister did it also. First (in another thread) he was polite :

==  Those are commonly 3 or more phase, but they aren't
==  steppers, they are designed for continuous spin.  They will 'step' when
==  you apply power to windings, but they aren't steppers and don't have the
==  low speed torque, it's a different type of motor.

In a second e-mail he was not so polite :

== If this is the SAME STUPID MOTOR that we already talked about, ***I***
== already explained to you that it IS **NOT** A STEPPER MOTOR!!!    *JUST*
== because you can power a coil and it goes to a position DOES NOT MAKE IT
== A STEPPER MOTOR.  *YOU* said you understood.  When I SAID it is not a
== STEPPER, I MEANT it is not a stepper.  Using your ignorance of what a
== stepper is, and it's ability to move to a point when you power a coil,
== STILL WON'T MAKE IT A STEPPER MOTOR!!!!  What part do you not
== understand???
==
==  AT THE VERY LEAST, *TELL* these more knowledgable people *WHERE*
== exactly you got the damn motor.  TELL them it is from the spindle of a
== hard drive.  THAT WAY they know to yell it into your stubborn head that
== THIS IS NOT A STEPPER MOTOR no matter what you think, you don't know
== enough to decide what is a stepper motor or not, and YOU HAVE DECIDED
== WRONG because you don't know how to test a motor at all for being a
== stepper.
==
==
==  Sorry if this is not the case, but it looks like you're using the same
== stupid motor I ALREADY told you is not even a stepper.  Not knowing
== something is one thing, not listening is another.  If this is the same
== motor you're being TERRIBLY TERRIBLY RUDE wasting their time trying to
== help you.  At the very least I already explained it is very important
== WHERE the motors come from on the drive and what type of drive, and
== making them have to waste time guessing what motor you have when you
== already know you should have told them is rather rude even if it's a
== different motor.  Especially if it's that same stupid spindle motor we
== discussed and you already had other evidence to suggest it is NOT A
== STEPPER MOTOR DAMMIT!
==
== What part of NO IT IS NOT A STEPPER do you not understand.  It is NOT
== well disguised, YOU are just too ignorant of how a STEPPER motor works,
== and also TOO IGNORANT of HOW OTHER MOTORS WORK (YES THEY 'STEP' LIKE I
== TOLD YOU BEFORE) to have the slightest IDEA of which is which.  WE
== ALREADY DETERMINED YOU DON'T KNOW, why do you insist on deciding again
== later that YOU DO KNOW???   YOU DON'T!!
==
==
== (which, BTW is being incrementally reduced
== by means of the comments and suggestions in this list).
==
==  I don't think it is reduced at all.  In fact, if this is the same
== motor, YOUR IGNORANCE HAS **INCREASED** GREATLY!  Get that in your head,
== *IF THIS IS THE SAME MOTOR YOU ARE DISCUSSING AGAIN, YOUR IGNORANCE IS
== EVEN *MORE* THAN WHEN WE TALKED ABOUT IT BEFORE!!!*  You have CONVINCED
== yourself that this motor is a stepper motor because it moves to a point
== when you power a coil, EVEN though I have explained otherwise YOU are
== resistant to that knowledge because YOU have taught yourself wrong.  You
== now have WRONG knowledge stuck in your head and are even WORSE than when
== you were just ignorant and didn't know, now you KNOW WRONG, and it is
== even harder to explain and convince you of what is right.  STOP TEACHING
== YOURSELF with no guidance.
==
==  And for your general info no stepper motor on a hard drive is going to
== have a 36W coil, of course if you had listened to me when I said this
== wasn't a stepper you wouldn't be doing something as dumb as trying to
== power this type of motor like that.
==
==  If this is a different motor and is a head stepper, what on earth
== makes you think it's supposed to be 12V?  Why do YOU decide to think
== that a motor that is only supposed to move a tiny part of a hard drive
== is supposed to have a lot of torque and take 3 amps?  You don't know
== anything about a hard drive, definitely not how much torque the motors
== are supposed to have, so how can you decide that 12 V would be right
== because there is less torque at 5V?  YOU don't know remotely how much
== torque you are supposed to have!  But it is not, it is the same damn
== stupid motor YOU already KNOW is not a stepper!  OR you would KNOW IT if
== you listened at all.  IT is a spindle motor, OBVIOUS by the numbers
== you're giving.

In other words and in a language accessible for people as dumb as me :
the spindle motors in most disk drives are brushless low profile DC motors.
The feedback for controlling these motors is taken from special marks
recorded in the disk surface and requires special IC drivers. You can
find details of these motors in :

http://www.pcguide.com/ref/hdd/op/spin.htm
http://home.fuse.net/Walts_Place/harddriveoperation.htm

I feel terribly guilty for my stupidity and I hope you will forgive me.
I sincerely hope also that the guy who sent me the abovementioned e-mail
have not had any heart disease due to my (sic) IGNORANCE, my stubborn
head and my damn stupid motor.

Anyway, thanks to all of you and, once again, excuse me.

Joan

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