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'[OT] stepper motor data..'
1999\05\23@083522 by paulb

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Janusz J. Mlodzianowski wrote:

> I have a couple of stepper motors disassembled from old 5.25"
> 360kB TEAC FDDs (FD-55BR-528-U). Motors work fine, but I do need more
> torque, so I am considering building new drivers (using e.g 1207).
> I would like to know more about motors.

 Mmmm.  I suppose http://www.doc.ic.ac.uk/~ih/doc/stepper/ doesn't help
so much as it is a different brand.  Motors in general, you will find
http://www.cs.uiowa.edu/~jones/step/index.html a good summary.

> The motor is driven via M54534P transistor array.  Can I increase
> torque by driving more current (how high),

 Frankly, I suspect the original would have been designed for near
maximum torque.  There is a limit on the current to which you can safely
subject the windings for one thing.  You may use conservation techniques
to limit idling current, but your concern for torque hints you may want
more than intermittent use.

> what is the winding sequence?

 Try this.  You know the brown is common.  Connect a speaker between
this and one other wire, then "flick" a single (1.5V) cell between the
brown and each of the other three.  The one which gives a healthy click
is the other side of the same winding.  Do the test with the other two
wires to confirm.

 I feel it to be rather silly to separate these motors from the drive
electronics, at least the part which is designed, presumably optimally,
to drive them.  Unless perhaps, you are concerned about size.

 In addition, it gives you a very versatile interface.
--
 Cheers,
       Paul B.

1999\05\23@091333 by Peter van Hoof

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If no motor data is available I suspect you could just give it a try. Most
industrial steppers I work with get quite warm (80 deg celsius or so) at max
torque and speed and I know the steppers in diskdrives do not.

There are (at least) these things to consider:
-Increasing the current thru the windings might not increase the magnetic
field due to saturation of the core (not likely but needs to be mentioned)
-Is the rotor a permanent magnet? if so you might demagnetise it with a too
high current.
-The max current (thus torque) could be limited by the current being the
maximum current for the winding diameter (most likely cause in small
steppers like these)
-The max current could be limited by winding heating max power /cubic mm
...a high motor temp would be an indication for this

As paul webster already suggests in his message if the ratio run/stopped is
low enough you could benefit from a reduced current when stopped and a
boosted current when running.

Peter

{Original Message removed}

1999\05\24@131057 by Brian Whittaker

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Janusz J. Mlodzianowski wrote:

> I have a couple of stepper motors from an old 5.25" Motors work fine, but I do
need more torque, so I am considering building new
drivers (using e.g 1207).

 IMHO floppy drives use unipolar 4 phase driving. A scheme that uses 1/2 of eac
h coil at a time. Alternating the side that is
driven alternates the effective magnetic polarity of the coil. One way to almost
double the low speed torque is to drive both sides
of each coil simultaneously with a PIC and bipolar driver using twice the motors
rated voltage because the coils are in series. The
more turns of wire you drive the larger is the generated magnetic force. If you
have power supply capacity to waste you can also use
a resistor to ballast the coil and operate it safely at a higher voltage. This w
ill increase the torque at high speed. For more on
this see this URL:
www.svskits.com/FreeInfo/Motion/Stpnote.htm
For a Schematic of a 1/2 bridge bipolar driver see this URL.
www.svskits.com/FreeInfo/Motion/Halfbrdg.htm
If you are driving only one motor then a full bridge driver would allow the use
of a more cost efficient power supply.

Disclaimer: these are information pages provided by the company I work for. Noth
ing is offered for sale on these pages . . Brian
--------------------------------------------
Brian Whittaker SVSKITS.COM
Voice: 510-582-6602 FAX: 510-291-2218
spam_OUTSVS_KITSTakeThisOuTspamMSN.COM URL: http://www.svskits.com

1999\05\24@135654 by Michael Shiloh

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>> I have a couple of stepper motors from an old 5.25" Motors work fine,
>> but I do need more torque, so I am considering building new
>> drivers (using e.g 1207).
>
>  IMHO floppy drives use unipolar 4 phase driving. A scheme that
>uses 1/2 of each coil at a time. Alternating the side that is
>driven alternates the effective magnetic polarity of the coil.
>One way to almost double the low speed torque is to drive both sides
>of each coil simultaneously with a PIC and bipolar driver using twice
>the motors rated voltage because the coils are in series.

I could be wrong, but didn't the original poster say he his motor had 5
leads? This would suggest an internal star connection, with 1 common lead
and 4 leads for the other ends of each coil. If I understand this correctly,
this would make it impossible to use in a bipolar mode.

It might be possible to carefully open the case and see if the internal
star connection can be opened, making each winding completely independent.

Comments? Corrections?

Michael Shiloh

1999\05\24@164242 by wagnerl

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Michael Shiloh wrote:
> I could be wrong, but didn't the original poster say he his motor had 5
> leads? This would suggest an internal star connection, with 1 common lead
> and 4 leads for the other ends of each coil. If I understand this correctly,
> this would make it impossible to use in a bipolar mode.
>
> It might be possible to carefully open the case and see if the internal
> star connection can be opened, making each winding completely independent.
>
> Comments? Corrections?
>
> Michael Shiloh


Oh ho.... I could be wrong too, but even in a star connection with 5
wires, you could use it in bipolar mode, since the middle of the star
(center of both double coils tied together) would always be aprox in
Vcc/2,  Just forget the common wire, or then attach it to a VCC/2
voltage point, or to a large capacitor to ground.

Think about it.  Even sudden high current from low impedance caused by
changes in the load and torque would generate a proportional voltage
drop on both coils of the same drive.  It could create a small
unbalanced voltage due differences in the internal coils, not perfect
impedances, but it would be so close that probably could be not
considered.

I never did it, but I don't see why it would be impossible.

Wagner

1999\05\24@174957 by Brian Whittaker

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-----Original Message starts -----
Michael Shiloh wrote ** edited **
I could be wrong, but didn't the original poster say he his motor had 5 leads?
This would suggest an internal star connection, with
1 common lead and 4 leads for the other ends of each coil. If I understand this
correctly, this would make it impossible to use in a
bipolar mode.
-----Original Message ends -----

Hi
 Actually It works just fine. The 5 wire motor is a modified 6 wire motor. When
driving the 6 wire motor in the bipolar mode the
center taps are left unconnected and float at 1/2 of the applied voltage. It doe
sn't matter which way current is flowing in the
coil, the voltage is always the same for both coils. In addition the inductance
and capacitance associated with each coil is the
same so the relationship holds for complex ac waveforms as well.

The 6 wire motor.
     coil#1A       coil#1B
     =====================
(gnd)---\/\/\/\---.---/\/\/\/----(+6v)
                 |
                 +--------------(+3v) <---.
                                          |**
                 +--------------(+3v) <---'
                 |
(+6v)---/\/\/\/---'---\/\/\/\----(gnd)
     =====================
     coil#2A       coil#2B

** this connection made to turn 6 wire motor into a 5 wire motor

 The 5 wire motor has the Center taps tied together, but connecting two equal p
otentials together has no effect on current flow. I
have done this many times and it has always worked. I suppose there are minor di
fferences in the coils and they do reduce efficiency
somewhat, but compared with the increase of torque they are not noticeable.

 I have not tried this with a chopper driver yet, but I think it may not work.
The small differences in coil impedance might cause
one coil to charge faster and turn off before the other does. In that event the
voltages would not be equal and strange things could
happen.

 The big problem is the 5 wire motor can not be connected correctly with only t
he information from an ohm-meter check because the
resistance from wire 1 to wire 2, 3, or 4, is the same. In fact the only wire yo
u can identify correctly is wire 5. the rest must be
found from the spec sheet or from trial and error.

A previous post, I forget by whom, to this list suggested using a speaker to fi
nd the correct wires.
 connect + 1.5 volts and one speaker lead to the center lead
 choose a wire at random and connect the other speaker lead
 momentarily connect the remaining leads to ground one at a time
 the lead with the loudest click matches the lead the speaker is connected to.
 the remaining two wires are the other coil

- This sounded like a good idea to me but I haven't tried it yet.
. . Brian

 Do not take the motor apart to trace the wires. The rotor of a stepper motor h
as many poles that must align exactly ( like within
a few 1000ths of an inch ) to the --gear-- teeth of the stators. To achieve this
accuracy the rotor is magnetized after the motor is
assembled. Taking it apart and putting it back together again usually destroys t
he alignment and the motor never works again. It may
turn but it will not produce the torque it was designed to.
--------------------------------------------
Brian Whittaker SVSKITS.COM
Voice: 510-582-6602 FAX: 510-291-2218
.....SVS_KITSKILLspamspam@spam@MSN.COM URL: http://www.svskits.com

1999\05\25@171238 by paulb

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Brian Whittaker wrote:

> One way to almost double the low speed torque is to drive both sides
> of each coil simultaneously with a PIC and bipolar driver using twice
> the motors rated voltage because the coils are in series. The more
> turns of wire you drive the larger is the generated magnetic force.

 Assuming you are not limited by power dissipation in the coils.

 If you *are* however, this logic is worthy of closer examination.  If
we put both windings in series across the *same* supply voltage, we
halve the current but with twice the turns, develop the same torque.
Each coil with half the current, dissipates one quarter the heat, but
there are now two, so half as much heat is dissipated overall at exactly
the same steady-state voltage.

 The *inductance* is now quadrupled however, but compensated by the
doubled resistance, the "charging" time is only doubled so the usable
motor speed is only halved in the process.

 OK, we can now increase the overall drive voltage by a factor of
sqrt(2).  This increases the torque by that factor and doubles the heat
in the winding so it now equates to the original single winding at the
original voltage.  It also increases the motor speed in proportion, so
we now have sqrt(2) times the original torque and 1/sqrt(2) times the
original speed.

 Interestingly, the power developed by the motor is half the torque
times the square of the angular velocity, which suggests that while this
alteration has increased torque (by sqrt(2)), it has reduced power
output by the same factor.

 Can someone spot a flaw in this reasoning?

(Please note that the two windings per pole share the same space and
thus the allowable power dissipation for driving the pair together is
the same as for only one at a time).
--
 Cheers,
       Paul B.

1999\05\27@145319 by Wagner Lipnharski

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"Paul B. Webster VK2BZC" wrote:
{Quote hidden}

I am not quite sure, I think that the difference between using a single
coil or two coils in series attached to the *same* drive VCC, as you
said, results in a half current, half dissipated power, but the torque
*would not be the same*, it should be less.  If this is true, than
multiplying the coil turns by 100, it will go for an infinite low
current and power, keeping the the same torque, what unfortunately I
think is not true. I really wish you would be right :)

I really don't know how to calculate some "gross" torque, but I believe
it has a direct relation to several factors in the motor, mainly applied
power.  There must have a "perfect" relation between torque, maximum
possible magnetic flux, core size (dictated by the winding coil size to
generate the maximum magnetic flux with the maximum current), and heat
dissipation.

Using a bipolar motor in a unipolar fashion (coils in series) almost
doubles the torque if you double also the VCC applied, but care need to
be observed to the dissipated thermal power.  A bipolar motor is
designed to stand one coild of each net energized all the time, not
both, so I think it is not a good idea to feed double VCC to the double
coil (unipolar) fashion.  First because the motor will dissipate double
heat, second that it will be trying to generate a double magnetic flux,
and the core can get saturated and the motor productivity would not be
the same as in bipolar fashion.

Each case is different, how long the motor is used (pwm, rest time and
so on), against real extra torque required from the motor.

I use bipolar motors in "H" bridges, but always try to feed them with
less than double voltage.

--------------------------------------------------------
Wagner Lipnharski - UST Research Inc. - Orlando, Florida
Forum and microcontroller web site:  http://www.ustr.net
Microcontrollers Survey:  http://www.ustr.net/tellme.htm

1999\05\27@181733 by paulb

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Wagner Lipnharski wrote:

> I think that the difference between using a single coil or two coils
> in series attached to the *same* drive VCC, as you said, results in a
> half current, half dissipated power, but the torque *would not be the
> same*, it should be less.

 Well, half the current through twice the turns = same *static* force.
However, I then went on to consider the apparently "disproportionate"
effect on the inductance of using twice as many turns, which affects
stepping speed.

>  If this is true, than multiplying the coil turns by 100, it will go
> for an infinite low current and power, keeping the the same torque,
> what unfortunately I think is not true. I really wish you would be
> right :)

 This is *not* the same as considering the situation where you have two
coils already wound and are deciding whether to use one or both in
series.

 If you use 100 times as many turns on a given former, then each turn
has 100 times the resistance as before (you have reduced its cross-
section by that factor).  You have therefore increased the resistance
10,000-fold and the magnetic field and thereby torque of a motor is
*reduced* to one-hundredth.

> There must have a "perfect" relation between torque, maximum possible
> magnetic flux, core size (dictated by the winding coil size to
> generate the maximum magnetic flux with the maximum current), and heat
> dissipation.

 You've twigged to it.  That was essentially my reply to the original
posting; if a motor is used at its design target, then "simple" changes
like using two windings instead of one, or just "bumping up the drive
voltage a little" will *not* necessarily increase performance *at all*.

> A bipolar motor is designed to stand one coil of each net energized
> all the time, not both, so I think it is not a good idea to feed
> double VCC to the double coil (unipolar) fashion.

 That's what I was saying!

> First because the motor will dissipate double heat, second that it
> will be trying to generate a double magnetic flux, and the core can
> get saturated and the motor productivity would not be the same as in
> bipolar fashion.

 That's what I was saying!

> I use bipolar motors in "H" bridges, but always try to feed them with
> less than double voltage.

 That's what I was saying!
--
 Cheers,
       Paul B.

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