CDROM Spindle Stepper motor

Correct. Some people do not understand that there is no fundamental difference between 'stepper motors' and ' brushless DC motors'. They both will move to a fixed position and stop when their coils are driven by DC, to make them spin continuously requires sequential coil drive, which is really AC not DC, isn't it ?

Have a look at the May 2008 issue of Silicon Chip, page 16. Leo Simpson argues that 'In reality, there is no such thing as a brushless DC motor', and I totally agree that the terminology is misleading.

WRONG !!!!

What makes you think a 'brushless DC motor' is any smoother than a 'stepper motor' ? How many poles does a 'brushless DC motor' have ? What is the size of the 'step' for a 'brushless DC motor' (they don't actually work with just DC, do they ?) How many poles does a' stepper motor' have ? Neither type has commutators, so any 'smoothness' is entirely due to the design of the drive electronics, and is ultimately limited only by the number of poles, isn't it ?

You clearly do not understand the construction of these types of motor. There is really f*ck-all difference between what is called a 'stepper motor' and what is called a 'brushless DC motor'. Mechanically, they are virtually identical. The differences lie mostly in the drive electronics (for the application), and the way the stator coils are terminated. A 'brushless DC motor' usually (but not always) has Hall-effect devices mounted to sense the rotor position and control the phase of the (typically)

Have a look at the May 2008 issue of Silicon Chip, page 16. Leo Simpson argues that 'In reality, there is no such thing as a brushless DC motor', and I totally agree that the terminology is misleading.

"fritz"

Brushless DC motors and stepper motors are the NOT the SAME - each type is suited to particular applications and they have very different characteristics.

See:

The see:

...... Phil

Why have you got 'steper motors' stuck in your 'brain' ?

CD players and CD-ROMs do NOT use stepper motors. None. Never.

geoff

Thanks Geoff. I used to repair CD players which at that time mostly used DC commutator spindle motors. One of the most common problems was the commutator becoming slightly erratic, causing increased rotational speed variations which caused the data from the disc to overflow/underflow the buffer. When you turn an unenergised stepper motor's shaft by hand, it jumps from one magnetically-held step to the next. Normal motors move smoothly and stop wherever you stop turning them. Leo Simpson's a good bloke, but I kinda doubt that he's an expert on the characteristics and applications of motors. Stepper motors and small linear-rotation motors all have magnets and coils but they don't all behave in the same way.

"Bob Parker"

A better name might be " Electronically Commutated Motors " - but that has no mass market appeal.

...... Phil

Well he's been nice to me in the past.

When I get a new SC I just skim through it for 15 minutes then give it to a mate who collects them, so I don't even remember seeing anything about motors (or anything much else in it).

Exactly!

That's what I call them. :-)

Well, with respect Geoff, I have disassembled probably far too many and an awful lot of them use a stepper to move the laser sled. As to the definition of the spindle motor, I don't really see the difference between a stepper and a brushless but I admit I'm not sure how you define the two types to see the difference, maybe you can clarify that?

Are you sure ? How can a stepper motor, with it's "quantised' discrete stepped positions track a continuous spiral groove ? My understanding is that all CD spindle motors are servo-controlled , to enable accurate tracking.

Could it be that people are not aware of what stepper-motors are. They are NOT the same as a multi-pole DC motor, as the OP seems to think, from his description ...

geoff

You don't understand what a spindle motor does, obviously. It just spins the disk, it has nothing to do with the tracking of the laser, which I have already explained. The spindle motor has feedback to spin the CD at the right speed, usually with Hall effect sensors. The coarse tracking is controlled by a separate motor with position feedback, and fine tracking is controlled with a 'voice coil' suspension connected to the laser lens.

Actually they are very similar in construction and theory. They both have a multi-pole rotor and a number of stator coils. They both will move to fixed position and stay there when a coil is energised by DC. To get either type to spin requires a controller to drive the coils in the correct sequence. The main difference is the coil terminations, steppers bring out all coils separately while so-called 'DC brushless' motors usually have the coils connected in star or delta (for 3-phase types).

ROTFLMFHO !!! You are obviously describing yourself there, Philthy !!!!!

They both have a multi-pole rotor and several stator coils, both will move the rotor to a fixed position when a coil is energised by DC. They have far more in common than you realise.

QUOTES from YOUR link above : 'Brushless DC electric motor......' 'Two subtypes exist: The stepper motor type may have more poles on the stator. The reluctance motor. '

"fritz the f*****ad "

Brushless DC motors and stepper motors are the NOT the SAME - each type is suited to particular applications and they have very different characteristics.

...... Phil

" fritz the f*****ad "

Brushless DC motors and stepper motors are the NOT the SAME - each type is suited to particular applications and they have very different characteristics.

Then FOAD.

...... Phil

QUOTES from YOUR link above : 'Brushless DC electric motor......' 'Two subtypes exist: The stepper motor type may have more poles on the stator. The reluctance motor. '

QUOTES from YOUR link above : 'Brushless DC electric motor......' 'Two subtypes exist: The stepper motor type may have more poles on the stator. The reluctance motor. '

Dude, I think I know eactly what a spindle motor does - I fix Denon, Sony, and Nad ones every week and have don for decades. Also DVD and DVD/CD-ROM/RWs.

None of these contain stepper motors, and I can't see how any other CD could, given the pusly buzzy motion that a stepper can only supply. I have never seen a CD with a spindle motor or a sled motor, that is a stepper. I have seen stepper motors in telex machines,printers, and iindustrial process machines.

Stepper motors move one discrete finite 'step' (surprisingly ?) for each discrete DC pulse that is sent to drive it. All CD motors I have ever seen are driven by a continuous DC, the voltage of which is finely varied to control the speed of the spindle, or the position of the sled.

Grateful you specify which make/model CD contains a stepper motor.

So now you are trying to fudg the distinction between stepper motors and the type you really mean. OK, I concede the I can therefore never 'win'.....

geoff

Have you ever seen a CD drive with a stepper motor ?

geoff

Sorry - slip of the keyboard. The Denon, Sony, and NADs are not, of course, stepper motors but CDs and DVDs....

geoff

Maybe you just have a problem with express> Are you sure ? How can a stepper motor, with it's "quantised' discrete

So what has the tracking of the 'groove' (sic) got to do with the spindle motor, which always was the obvious subject ?