Can anyone help me figure out a DC motor that I took from an old CDrom drive? It seems to be a brushless DC motor and was the one used to spin the CD. It is mounted on a small PC board attached to a narrow ribbon cable.
The question is that this ribbon cable that attaches to the PC board has 11 leads. My question is what are all those leads for? I've googled for answers but haven't found any. Stepper motors, yes. But this one not yet.
> Can anyone help me figure out a DC motor that I took from an old CDrom
> drive? It seems to be a brushless DC motor and was the one used to
spin
> the CD. It is mounted on a small PC board attached to a narrow ribbon
> cable.
>
> The question is that this ribbon cable that attaches to the PC board
has
> 11 leads. My question is what are all those leads for? I've googled
> for answers but haven't found any. Stepper motors, yes. But this one
> not yet.
The usual answer with these is that those extra leads are for the hall
effect sensors. Most of these low-cost brushless motors are not
commutated at the motor; there is a controller chip somewhere else that
does the job. To get the information about the rotationnal position of
the windings, you can either use Hall sensors or do some back-emf
detection. Hall is usually cheaper.
So the cable would break down like this:
3 coils @ 2 ea = 6 wires
3 Halls @ 1 ea = 3 wires
Hall + & - = 2 wires
Note that often the Halls run on less than 5V, derived from the 5V rail
via a (very important) current-limiting resistor.
> Hi Group,
>
> Can anyone help me figure out a DC motor that I took from an old CDrom
> drive? It seems to be a brushless DC motor and was the one used to
> spin the CD. It is mounted on a small PC board attached to a narrow
> ribbon cable.
>
> The question is that this ribbon cable that attaches to the PC board
> has 11 leads. My question is what are all those leads for? I've
> googled for answers but haven't found any. Stepper motors, yes. But
> this one not yet.
3 x magneto resistive sensors a' 2 pins each = 6
2 pins to feed power to the mr sensors = 2
3 phases wye connected = 3
total = 11
Lindy,
The CD spindle motors in front of me have only 2 terminals directly on the
motor. The ribbon cables (12 way in my case) are connected to the laser
head assembly.
Yours could well be different as I guess there are a large number of
variations. The previous answer relating to hall sensors sounds feasible.
Do you have the rest of the CDrom that you could trace the connection back
to a likely looking driver chip or discrete transistor.
The rotational speed is often measured from the optical output so motor
speed sensors are not always required.
Richard P
"Lindy Mayfield"
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Hi Group,
Can anyone help me figure out a DC motor that I took from an old CDrom
drive? It seems to be a brushless DC motor and was the one used to spin
the CD. It is mounted on a small PC board attached to a narrow ribbon
cable.
The question is that this ribbon cable that attaches to the PC board has 11
leads. My question is what are all those leads for? I've googled for
answers but haven't found any. Stepper motors, yes. But this one not yet.
Thanks to all. I don't have it in front right now, but it is from a 3'rd generation old Dell Optiplex GX1 (or GXa) that was in a fire.
But this solves my curiosity that the connections are for feedback for speed or position. I guess a CD ROM drive needs to run at a regulated speed or that the drive needs to know just where it is in the spin phase.
Actually I'm scavenging for things for robots, maybe a BEAM robot, but I'm still new at this all.
How do you normally figure these things out? I see one way is to try to figure it out from the physical characteristics of the motor and from what it is connected to on the board.
I had a stepper motor from a thrown away PC's 5 1/4 floppy. I figured it out by reading about steppers on the net and taking two 5v wires and I found when I simply raked one wire across the leads it would step! I managed to program a Pic to control it, then I connected the Pic to my PC's serial where I could send it commands to step forward and backwards. That was cool! I felt like I'd really done something then. (-:
On Mar 30, 2005, at 2:41 PM, Lindy Mayfield wrote:
>
> Actually I'm scavenging for things for robots...
Older, slower CD drives (and probably STILL audio CD drives that
only need to run a '1x' speed) used normal DC brushed motors for
the spindle.
Higher speed spindle motors on CD and HD drives are usually three
phase brushless motors with hall sensors used for feedback to
create the proper drive waveforms (not so much exact speed control,
although that follows as well.) Most of the ones I've seen have
the three phases connected in either Delta (3 connections) or Wye
(4 connections), with additional connections for the hall sensors.
In the drive, these motors are drive by high-integration wonder
chips that connect to all the pins on the motor, plus assorted
inputs from a microcontroller, plus (frequently) other outputs
for the other motors and things in a typical drive. Most of
the drives I've dissected use Rhom chips that are particularly
hard to find spec sheets for, especially if they're not the
"current" generation, but here's a representative sample:
Power to each coil seems to be on the order of an amp. I have
not seen simple circuits to do anything useful with these motors,
but it ought to be possible, I keep thinking, even if it is in
somewhat "jerky" stepper fashion... I also haven't been very
successful using the original driver chips to drive the motors;
they seem to require quite a bit of 'housekeeping' or something...
Now, if you're into remote control, there's a whole movement
in taking these spindle motors and turning them into high power
brushless motors for driving your propeller in an electric plane.
This requires a controller of considerable complexity or expense
(>$50 for commercial units), but is getting wonderfully documented:
www.rcgroups.com/forums/showthread.php?s=&threadid=127606 http://www.gobrushless.com
All you do is replace the magnets, rewind the coils, put in better
bearings... These guys are crazy, but they're getting performance
equal to $60 motors from $10 worth of parts and some time.
Let us know if you discover anything particularly interesting...
> Higher speed spindle motors on CD and HD drives are usually three
> phase brushless motors with hall sensors used for feedback to
> create the proper drive waveforms (not so much exact speed control,
> although that follows as well.) Most of the ones I've seen have
> the three phases connected in either Delta (3 connections) or Wye
> (4 connections
> Now, if you're into remote control, there's a whole movement
> in taking these spindle motors and turning them into high
> power brushless motors for driving your propeller in an
> electric plane.
> This requires a controller of considerable complexity or
> expense (>$50 for commercial units), but is getting
> wonderfully documented:
> www.rcgroups.com/forums/showthread.php?s=&threadid=127606
> http://www.gobrushless.com
> All you do is replace the magnets, rewind the coils, put in
> better bearings...
Yes. I've rewinded one of these brushless motors. And changed the magnets,
too. The resulting motor is really a beast of torque, for its size. It can
easily hover a little RC airplane, hanged from the propeller!. But the
changes in the windings and magnets are only to improve performance. The
motor can run as it is equally well.
> These guys are crazy, but they're getting
> performance equal to $60 motors from $10 worth of parts and some time.
These are (almost) all brushless motors, with a "rotating can" in wich the
permanent magnets lie. In fact, the stator is actually the windings,
normally 9 of them, in delta or wye configuration. The magets rotate with
the can and the CD-ROM in the drive, and are usually a cheap type one, with
12 poles arranged NSNSNSNSNSNS.
These motors are conceptually the same as the AC synchronous machines, only
the stator and rotor interchanged, and permanent magnets replacing DC
inductors (rotor, excitation). These are good motors to manage speed and
torque, but not as good for positioning. At least not until introduction of
new generation inverters. Nowadays, inverters from ABB or Siemens can easily
control position using these kind of motors. I am talking here of big
machines, in places like rolling mills, for example.
Lindy,
You did really do something. A traditional "hack".
Congratulations
Bill
----- Original Message -----
From: "Lindy Mayfield" <.....Lindy.MayfieldKILLspam@spam@eur.sas.com>
To: "Microcontroller discussion list - Public." <piclistKILLspammit.edu>
Sent: Wednesday, March 30, 2005 2:41 PM
Subject: RE: [EE] Help Understanding DC Motor from CD Player
snip snip snip
>
> I had a stepper motor from a thrown away PC's 5 1/4 floppy. I figured it
out by reading about steppers on the net and taking two 5v wires and I found
when I simply raked one wire across the leads it would step! I managed to
program a Pic to control it, then I connected the Pic to my PC's serial
where I could send it commands to step forward and backwards. That was
cool! I felt like I'd really done something then. (-:
>
>
The spindle motors I have here must be the older type.
RP
"Lindy Mayfield"
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It is connected to an IC labeled BA6858FM. Only one hit on Google and the
page is completely in Chinese. (-:
The older stuff is definitely easier to figure out.
> Actually I'm scavenging for things for robots, maybe a BEAM robot, but
> I'm still new at this all.
Some people build electric airplane models using those motors. They can
be pushed quite far apparently.
> How do you normally figure these things out? I see one way is to try
> to figure it out from the physical characteristics of the motor and
> from what it is connected to on the board.
The motor coil phases show 2 to 10 ohms between them. The gmr sensors
show 400 to 1200 ohms between each pair of outputs and ~3k between the
ends (where you apply power). The only way to knwo for sure is to remove
the rotor and trace the pcb.
This was very interesting. After I finally found the right screw driver bit (TORX #8) and got the old HD apart it wasn't anything like I expected.
First there was no stepper motor. The arm at the back end was a coil of wire between two *very* powerful magnets. After I finally got the platters off and down to the motor, I was baffled. It seems that it's built right into the aluminum chassis of the drive! Is this right?
Well I always have the wind chimes option from the page you mentioned. (-:
I've got a box of these, bet there's some clever new use they can be
put to
> After I finally got the platters off and down to the motor, I was baffled.
> It seems that it's built right into the aluminum chassis of the drive! Is
this
> right?
Well, they're pretty low profile. I haven't one handy but ISTR that there
were three very short wires - red, green and black I think, like this one
but shorter
On Apr 1, 2005, at 10:06 AM, Lindy Mayfield wrote:
> After I finally found the right screw driver bit (TORX #8) and got
> the old HD apart it wasn't anything like I expected.
I've taken apart lots of drives. It's fun :-)
> First there was no stepper motor. The arm at the back end was a coil
> of wire between two *very* powerful magnets.
"voice coil positioner." Though they don't look as much like voice
coils
as they did in the old days. The magnets are among the more useful bits
you can rescue from disk drives. (take apart a $100 disk drive, get a
$2 magnet. Oh joy. (Of course, by this time, the drives are no longer
worth $100.))
> After I finally got the platters off and down to the motor, I was
> baffled. It seems that it's built right into the aluminum chassis of
> the drive! Is this right?
That's pretty common these days, but not universal (it may be universal
in
NEW drives, but not the ones I've been taking apart.) The Aluminum case
is part of the heatsink for the motor...
> After I finally got the platters off and down to the motor, I was
> baffled. It seems that it's built right into the aluminum chassis of
> the drive! Is this right?
I opened up one recently, and indeed the motor is part of the chassis.
Nobody said it would resist being handled with a punch and a hammer,
though:-). I guess I was lucky, because I could wack the shaft from
the outside. So I have a brushless motor now, but no controller. Next
project.
> After I finally got the platters off and down to the motor, I was
> baffled. It seems that it's built right into the aluminum chassis of
> the drive! Is this right?
I opened up one recently, and indeed the motor is part of the chassis.
Nobody said it would resist being handled with a punch and a hammer,
though:-). I guess I was lucky, because I could wack the shaft from
the outside. So I have a brushless motor now, but no controller. Next
project.
mit.edu> 
