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'Stepper Motors'
1996\03\19@100659 by muel Yerardi

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> ...how can I increase the number of steps?...

If you can get a copy of the January 1994 issue of Embedded Systems
Programming there is an excellent writeup on driving stepper motors using
an 'hc11.  Basically what he describes is a unipolar drive that is driving
a 200-step motor.  The unipolar drive utilizes 4 MOSFETs, each driving on
of the four windings of the motor.

Here is the full-stepping sequence:

STEP    Q1      Q2      Q3      Q4
1       ON      OFF     ON      OFF
2       ON      OFF     OFF     ON
3       OFF     ON      OFF     ON
4       OFF     ON      ON      OFF

Here is the half-stepping sequence:

STEP    Q1      Q2      Q3      Q4
1       ON      OFF     ON      OFF
2       ON      OFF     OFF     OFF
3       ON      OFF     ON      OFF
4       OFF     OFF     OFF     ON
5       OFF     ON      OFF     ON
6       OFF     ON      OFF     OFF
7       OFF     ON      ON      OFF
8       OFF     OFF     ON      OFF

Hope this helps.

Sam Yerardi
Innovative Solutions
spam_OUTsyerardiTakeThisOuTspamzoomnet.net


'Stepper Motors'
1996\08\23@184735 by Philip Lalone
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       Is it possible to control a stepper motor from a PIC16c84, how
would I go about doing this?

                                               Philip Lalone
                                               .....plaloneKILLspamspam@spam@alphax.com
                                               Alpha-X Development

1996\08\25@140251 by Mark K Sullivan

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Driving stepper motors can be as difficult as you want to make it.  Driving
steppers can also be real easy if you're not after maximum performance.

You need a power supply (more on that in a moment) and a switch for each coil.
The basic principle is to switch the coils on and off in sequence to create a
rotating magnetic field.  Reverse the sequence and they go backwards.  Stepper
motors may be have permanent magnet rotors or unmagnetized rotors.  The latter
are called "variable reluctance" and are less common than the permanent magnet
type.  You can tell the difference because a PM motor has a "cogging" effect
where you can feel the poles as you turn the shaft by hand with no current
applied to the windings.  In contrast, an unenergized VR motor turns freely.

Permanent magnet stepper motors come in bipolar and unipolar flavors.  Bipolar
motors have a simple winding for each "phase" or set of poles.  You have to be
able to drive current through the winding both ways (i.e. the electrical drive
needs to be bipolar).  This is typically accomplished with an H bridge.
Unipolar motors have a biflar winding with wired so you can reverse the flux of
the pole by energizing one or the other winding with a unipolar drive circuit.
Unipolar is pretty common.  A VR motor doesn't care about polarity so you only
need a unipolar drive.  Unipolar drive uses an open collector transistor for
each half winding (i.e. two per biflar winding, one for each direction).  If a
PM stepper has four wires, it is a two-phase bipolar type.  If it has 6 or 8
wires, it is *probably* a unipolar two-phase type.

The power supply can either be a constant voltage type, which is easy or
something more sophisticated.  Because the motor's windings are inductors,
simply applying a square voltage waveform results in a current ramp.  As you
switch through the phases faster and faster, the current never gets a chance to
ramp up and torque is low.  At some speed, the motor will quit working at all.
To overcome this, stepper power supplies have used a variety of tricks to
deliver a higher voltage to the winding when it is switched on and a lower
voltage as it saturates.

One obvious (and good) choice is a constant current supply.  Because of the
power levels are large, these are typically implemented with a high frequency
switching circuit that maintains a constant average current.  The other
advantage of switching is that you can use the same switching transistor that
selects the phase to chop the winding for constant current.  There are a number
of commercial drives and stepper motor drive ICs that work this way.  Note that
you really need multiple constant-current supplies, one for each concurrently
energized winding.  A two phase motor needs two.

A low performance but easy solution often seen is L/R or L/4R drive where a
resistor is wired in series with the motor winding and the power supply voltage
raised to the point that the winding still sees rated static current.  For
example, a 5 volt stepper with L/4R drive and 10 ohm windings would have a 40
ohm resistor in series and require a 25 volt power supply.

In applications where the motor runs at substantially constant speed, the proper
voltage for that speed may be pre-determined and a two level constant voltage
supply may be used.  The supply switches to high voltage when the motor is
running and back to low voltage when the motor is holding or running at low
speed.

Because the motor is open loop, you lose track of the position if you try to
accellerate or decelerate too fast.  You must ramp the step rate up and down,
not just start and stop stepping at full speed.  A simple trapezoidal speed/time
profile is adequate.  Certain step rates may cause the motor or the mechanical
system to resonate.  This can cause loss of accuracy.  When you are ramping the
motor up to speed is a good time to experience this problem as the accelerating
step rate passes through the resonant frequency.  A technique called
half-stepping may help with resonance.  Half stepping is a simple case of
micro-stepping where you partially energize two phases at once with a current
ration that reflects an intermediate position between gross motor steps.  If I
start explaining this, this "quick note" is going to get way too long.

The short answer is:
1> Get a stepper motor data book from Superior Electric.  They explain a lot of
this stuff.  Another good data book is from North American Phillips Controls
Corporation.  They also sell a drive chip.

2> Read about stepper motor drive chips.  SGS makes some.  The L298 is popular.

3> Hook the four windings of a unipolar, two-phase PM motor between four
open-collector transistors and a power supply at the motor's nameplate voltage.
Put a diode across each winding to soak up the inductive spike.  Drive the bases
(or gates) of the four transistors from the PIC.  Now you can experiment without
burning anything up.  Lets say you have the windings like this (color code for
Superior Electric 6 wire motor, white and black to V+):
Phase A forward (red) - PA0
Phase A reverse (red with white stripe) - PA1
Phase B forward (green) - PA2
Phase B reverse (green with white stripe) - PA3
This is the bit pattern sequence you send out port A.  Start at 10 steps per
second or so.
0101
0110
1010
1001
and repeat.
Reverse the sequence to rotate backwards.  If the motor just buzzes, you
probably have the windings wired up in the wrong order.

How many wires and what colors does your motor have?

- Mark Sullivan -

1996\08\25@211047 by Philip Lalone

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On Sun, 25 Aug 1996, Mark K Sullivan wrote:

> How many wires and what colors does your motor have?

I got a stepper motor from a 1.44 floppy drive, 4 wires, blue, red, white,
yellow.  I assumed that 2 of them needed to be grounded, and I sent 00,
01, 11, 10 to the port, it didn't move at all :)

                                               Philip Lalone
                                               plalonespamKILLspamalphax.com
                                               Alpha-X Development

1996\08\25@212128 by Prashant Bhandary

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At 07:38 PM 25/08/96 -0700, you wrote:
>> How many wires and what colors does your motor have?
>
>I got a stepper motor from a 1.44 floppy drive, 4 wires, blue, red, white,
>yellow.  I assumed that 2 of them needed to be grounded, and I sent 00,
>01, 11, 10 to the port, it didn't move at all :)

I've played around with one of those. It is a bipolar stepper. Drive the
windings
with H bridges. I once controlled one of those using the parallel port on a
PC and an L293. Details are at ftp.ee.ualberta.ca in
/pub/cookbook/comp/parallel.
The file is called flpystpr.zip.

Regards

Prashant
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 Prashant Bhandary             | Tel:  +61-2-9662 5299
 Spatial Information Solutions | Fax:  +61-2-9662 5348
 Roads and Traffic Authority   | Email: .....prashbKILLspamspam.....rta.nsw.gov.au
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--------------------------------+---------------------------------

1996\08\26@064020 by R.J.Smith

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On Fri, 23 Aug 1996, Philip Lalone wrote:

>         Is it possible to control a stepper motor from a PIC16c84, how
> would I go about doing this?
>
>                                                 Philip Lalone
>                                                 EraseMEplalonespam_OUTspamTakeThisOuTalphax.com
>                                                 Alpha-X Development
>

Philip,

The short answer is yes. I did it by using a simple look-up table for the
coils and then had counter to hold the position information. Then by
cycling through (left or right) the stepper can be controlled very easily.

I hope this has been of help.

Rich


Department of Applied Physics, University of Hull, HU6 7RX
Tel 01482 465135  Fax 01482 465606 // E-mail R.J.Smithspamspam_OUTapphys.hull.ac.uk

1996\08\26@085635 by Mark K Sullivan

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Philip:

Measure continuity with an ohm meter.  You will probably discover that you have
two windings.  If so, this is a two-phase bipolar motor.  If all four wires
are interconnected, this is a three-phase unipolar motor.  In the latter case,
find the common wire (the one with the same DC resistance each of the remaining
three).

If it's bipolar, you need two H bridor each winding.  Now use the four
bits to drive each winding forward or reverse polarity.

If it's three-phase, connect common to +12V and ground the three coils one at
a time like this:
0001
0010
0100
and repeat.

You can experiment with phase switching sequences by hand.  Get a bunch of
clip leads and wire up the motor for each phase pattern one at a time.  When
you energized each new phase pattern, the motor should "clunk" and advance a
little bit.

- Mark Sullivan -


'Stepper motors'
1999\04\19@141844 by Alan King
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 Finally found my data book I was going to recommend..  Sure enough,
look it up and it's on the web.  Haven't seen it mentioned before, and
everyone using stepper motors should read through this at least once,
and have it on hand for reference.

http://www.compumotor.com/catalog_eng_ref.htm

 I haven't actually downloaded it yet to check, but their data book is
the best stepper motor theory through application info I've ever found
in one place, and from the headings this looks to be a complete online
version.  You will be a stepper motor engineer after reading this, just
hope it's in time to help..

Alan




Lawrence Lile wrote:
{Quote hidden}

1999\04\19@161831 by Lawrence Lile

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Thanks, Alan!


-----Original Message-----
From: Alan King <@spam@shadedemonKILLspamspammindspring.com>
To: Lawrence Lile <KILLspamlilelKILLspamspamtoastmaster.com>
Cc: RemoveMEPICLISTTakeThisOuTspamMITVMA.MIT.EDU <spamBeGonePICLISTspamBeGonespamMITVMA.MIT.EDU>
Date: Monday, April 19, 1999 1:17 PM
Subject: Re: Stepper motors


{Quote hidden}

motors,
{Quote hidden}

true
>> at higher speeds or do they smooth out?
>>
>> Here's some information I've gathered so far, but have not completely
>> digested:
>>
>> http://www.eio.com/stepindx.htm   Surplus supplier kindergarden intro to
>> stepper motors.  Has a neat link to an artist/genius who made a stepper
>> motor controlled easter egg painter...
>>
>> http://servolink.com/gearspec.htm    Servolink corp - CHEAPEST good
quality
>> delrin gears and good engr. information.  Online gear calculators!
>>
>> ftp://ftp.armory.com/pub/user/rstevew/     FTP site with several
interesting
>> articles about steppers, H bridges, electronics, etc.


'Stepper Motors'
1999\09\12@020311 by Greg Hastings
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<x-flowed>Hi,

 I am still fairly new to electronics and have a pretty basic question on
using the PIC to controll stepper motors.

 I wrote a simple program to send out the pulses and I did get a motor to
turn but it turns very weakly.  My guess is that the PORTA voltage levels
are too low.  I have heard one can use transistors and a separate larger
voltage level to increase the power of the motor.

 So I added four 2222 NPN transistors w/ the base of each connected to the
PORTA.0 - PORT.3 bit outputs.  I had +9V from a wall wart going into the
emmitter and then the collector was connected right to one of the motor
inputs.  With this addition to my circuit the motor does not turn at all.  I
have also tried swapping the emmitter and collector but that fails as well.
Anyone know why this is so?

Greg (TakeThisOuTghpicEraseMEspamspam_OUThotmail.com)

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</x-flowed>

1999\09\12@032738 by Greg Brault

picon face
I recently played around with this.
try putting resistors going to the base, you may be overdriving them and the
PORTB pins.
Also, if you have tried to swap emitter and collector, you may have blown the
transistor.  Also, since all the current in a transistor flows through the
emitter, have your stepper motor wire connect to that, and then going to ground
(for an NPN) or + (PNP)

Greg Hastings wrote:

{Quote hidden}

1999\09\12@122716 by Dave VanHorn

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>   I wrote a simple program to send out the pulses and I did get a motor to
> turn but it turns very weakly.  My guess is that the PORTA voltage levels
> are too low.  I have heard one can use transistors and a separate larger
> voltage level to increase the power of the motor.

You're lucky the micro still runs!  No micro is going to have enough output
to run a stepper without some huge drivers.

>   So I added four 2222 NPN transistors w/ the base of each connected to
the
> PORTA.0 - PORT.3 bit outputs.  I had +9V from a wall wart going into the
> emmitter and then the collector was connected right to one of the motor
> inputs.  With this addition to my circuit the motor does not turn at all.
I
> have also tried swapping the emmitter and collector but that fails as
well.
> Anyone know why this is so?

Most likely, a problem with turning the 2222s on and off.
The low output voltage of your micro may not be low enough to turn off the
2222s.
Try using one of the open collector driver chips.  ULN2003 or similar.

1999\09\12@132148 by Bob Blick

face
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>  So I added four 2222 NPN transistors w/ the base of each connected to the
>PORTA.0 - PORT.3 bit outputs.  I had +9V from a wall wart going into the
>emmitter and then the collector was connected right to one of the motor
>inputs.  With this addition to my circuit the motor does not turn at all.  I
>have also tried swapping the emmitter and collector but that fails as well.

I'm surprised it didn't work when you had positive to collectors and
stepper leads to emitters. Maybe this is a 4 wire stepper? If it is a 5 or
6 wire stepper, try this:

All the emitters go to PIC ground, along with the negative of your wall
wart. Positive of the wall wart goes to the common(5 wire) or commons(6
wire) of your stepper. The four collectors each get a stepper lead. Put
resistors between PIC and base! Let's say 220 ohms.

This doesn't give you snubbing, but depending on the size of your motor you
might get away with it.

If your stepper is a 4 wire forget what I said, it won't work because
you'll need bipolar drivers.

-Bob

http://www.bobblick.com/

1999\09\12@133017 by Dave VanHorn

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> All the emitters go to PIC ground, along with the negative of your wall
> wart. Positive of the wall wart goes to the common(5 wire) or commons(6
> wire) of your stepper. The four collectors each get a stepper lead. Put
> resistors between PIC and base! Let's say 220 ohms.

Another note here, don't try to run the stepper from the supply that feeds
the micro.
Separate supply (common ground) or batteries is easier to get working.

1999\09\13@200230 by Peter Homann

picon face
Hi,

Usually they use a small dc motor and a gear train to the pot shaft. It's
all open loop. Apply voltage to the motor until the music is loud enough.
That sort of thing.


Oatley Electronics at http://www.oatleyelectronics.com sell them. They even
have a kit to control it via infrared remote control.

Redards,

Peter.


Peter Homann   email: peterhEraseMEspam.....adacel.com.au       Work : +61 3 8530-7755
Adacel Technologies Ltd                          Fax  : +61 3 9596-2960
250 Bay St, Brighton 3186, VIC, AUSTRALIA      Mobile :     041 4494578
http://www.adacel.com.au     Australian Software Engineering Excellence


> {Original Message removed}

1999\09\14@124912 by Erik Reikes

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At 12:27 PM 9/12/99 -0500, you wrote:
>> All the emitters go to PIC ground, along with the negative of your wall
>> wart. Positive of the wall wart goes to the common(5 wire) or commons(6
>> wire) of your stepper. The four collectors each get a stepper lead. Put
>> resistors between PIC and base! Let's say 220 ohms.
>
>Another note here, don't try to run the stepper from the supply that feeds
>the micro.
>Separate supply (common ground) or batteries is easier to get working.

I can reiterate this advice.  The coils of your motor are giant inductors
across which you are switching full supply voltage.  When you start running
the thing quickly it will reset your micro.

When I built a micro-stepper motor driver for an art project I used a
couple of NPN's to drive the coils of a SPDT relay.  My motor had 4 wires
and I had to alternate between +/- voltages.  The order of alternations on
the wires caused to to turn in opposite directions.  The way I figured it
out is to use a multimeter to figure out which wires went with which coils
(there will be maybe 100 ohms resistance between pairs of wires).  Then I
sat there for about 20 minutes with a 5 volt power supply and and touched
wires here and there until I could get the thing to turn around and learn
the sequence.

It looked like an encoder :
00
10
11
01
00

was CW

and

00
01
11
10
00

was CCW.

Test out each individual part separately without the micro.... i.e. use
twisted wires and your relays/transistors to drive the motor by hand then
hook to your micro.  Make sure you start the pulse counting slow, because
if you go too fast you will saturate the relays as they have a max switch rate.

-Erik Reikes

1999\09\14@192548 by Gennette Bruce

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       Stepper motors
       <snip>
> Test out each individual part separately without the micro.... i.e. use
> twisted wires and your relays/transistors to drive the motor by hand then
> hook to your micro.  Make sure you start the pulse counting slow, because
> if you go too fast you will saturate the relays as they have a max switch
> rate.
>
> -Erik Reikes
>
       Relays ???,  Common 0 volts ???
       Get with the modern approach - opto isolation between 2 *COMPLETELY*
separate circuits.

       Many advantages are gained, not least freedom from inductive
interference and ground loops, and you can physically separate the circuits
by at least 5m of ribbon cable. If you build the opto couplers by hand, ie.
use discrete LEDs and photodiodes, you can separate them by 20m of cheap
optical fibre (clear, thick fishing line).

       Hint - if you fit a reverse biased diode across the opto coupler LED
and a large value (1M) pull down onto the base of the phototransistor in the
opto coupler you will be able to achieve *CLEAN* switching up to the maximum
rate the stepper motor can handle.

       Bye.

1999\09\14@195246 by Greg Hastings

picon face
<x-flowed>Is there a relay (available from Jameco or Mouser) that you recommend I use?
 The motor for this project just says 12V on it.

Some other motors I have just say Vexta DC 1.2Amp, 0.8Amp, and 3.3 ohm, 7.5
ohm respectively.  What voltage and relay should I drive these last type of
motors at?

Greg

{Quote hidden}

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</x-flowed>

1999\09\15@003039 by Erik Reikes

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At 09:24 AM 9/15/99 +1000, you wrote:
>        Relays ???,  Common 0 volts ???
>        Get with the modern approach - opto isolation between 2 *COMPLETELY*
>separate circuits.
>

Are you talking about optcoupling to a relay to do the switching or do you
want your photodiodes to be switching the possibly high currents of a big
motor?  There are problems with switching _large_ current through an
opto-isolator.  I'd think 50mA or so would be tops, then you have to go to
something bigger like a MOSFET, or whatever.

Not much of an analog guy myself.

Good luck

-E

1999\09\15@134334 by Edson Brusque

face
flavicon
face
> >     Does anyone knows how motorized pots (rotatives and
> > sliders) works?
> > Where can I find infos on the web about it?
> Usually they use a small dc motor and a gear train to the pot shaft. It's
> all open loop. Apply voltage to the motor until the music is loud enough.
> That sort of thing.
> Peter.

   Peter and all,

   There are a kind of motorized pots used on automated audio mixers and
other audio gears that moves to an absolute position.

   With an automated audio mixer, you could make things like program the
guitar track to raise volume from 50% to 80%, for the guitar solo in the
middle of a song, and then go back to 50% (and obviously, some much more
complicated things).

   This is the kind of motorized pots I need.

   Thanks and regards,

   Brusque

___________________________________________________________________________
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1999\09\15@135148 by paulb

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Edson Brusque wrote:

>   Does anyone knows how motorized pots (rotatives and sliders) works?

 Small DC motor and gearbox AFAIK.  No feedback in domestic
applications.  If there are "professional" versions I can't answer for
them.
--
 Cheers,
       Paul B.

1999\09\21@113340 by Wagner Lipnharski

picon face
Let's not do confusion between "opto-coupler" and "opto-driver", the
first one acts as a bare low power connection, while the second can be
considered a large power transistor with an opto-gate/base.
Wagner.


Erik Reikes wrote:
{Quote hidden}

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