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'[OT]: Stepper motor sequence question'
2001\04\25@153005 by Joan Ilari

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Hi, PicListers

I have built a 3 wheel rover powered by two unipolar 4 phase
stepper motors (one wheel is free). Each motor is controlled
(of course!) by a PIC. According to the motor datasheet,
the motor stepping sequence should be :

A -A / A -B / B -B / B -A

that is, powering always two windings. However, if I use the
sequence

A / B / -A / -B

I do not appreciate any traction difference (and I spare 50 % power).

To test this I have powered one wheel with the first sequence and
the other one with the second one. No traction difference at all.

Any clue ?

Thanks

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2001\04\25@160145 by michael brown

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Sorry, I can not answer your question.  However, I would like to know what
kind of motors you are using.  I too am building (glomming together :-) ) a
similar thing.  I was trying to use some stepper motors I obtained from old
5.25" floppy drives.  But they are not powerful or fast enough.  I built a
pic-controlled motor controller using TIP-120 transistors as drivers.  I
need to keep this as cheap as possible.

Michael Brown
Instant Net Solutions
http://www.KillerPCs.net

{Original Message removed}

2001\04\25@162034 by Quentin

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Try this:
http://www.piclist.com/techref/io/steppers.htm

Quentin

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2001\04\25@172722 by steve

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> According to the motor datasheet,
> the motor stepping sequence should be :
>
> A -A / A -B / B -B / B -A

This is called "full-step drive" and it provides the most torque over
the speed range.

> that is, powering always two windings. However, if I use the
> sequence
>
> A / B / -A / -B

This is called "wave drive" and produces less torque but is more
susceptable to motor resonance problems which probably aren't an
issue in your situation.
The advantage is the power consumption (as you know) and that
when you remove the power, the motor doen't move half a step to
its resting (detent) position. Again, not really an issue for you but it
is in some cases.

> To test this I have powered one wheel with the first sequence and
the
> other one with the second one. No traction difference at all.

If you keep adding weight to your vehicle, you'd eventually find that
it would start to go round in circles as the wave driven motor
started missing steps.

Steve.

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TLA Microsystems Ltd         Microcontroller Specialists
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2001\04\26@060224 by Roman Black

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Joan Ilari wrote:

> I have built a 3 wheel rover powered by two unipolar 4 phase
> stepper motors (one wheel is free). Each motor is controlled
> (of course!) by a PIC. According to the motor datasheet,
> the motor stepping sequence should be :
>
> A -A / A -B / B -B / B -A
>
> that is, powering always two windings. However, if I use the
> sequence
>
> A / B / -A / -B
>
> I do not appreciate any traction difference (and I spare 50 % power).


Hi Joan, both are full-step systems. The top one
is called "2 windings on" the bottom one is
"1 winding on" or "wave mode".

Mathematically the top one has 1.41 (41% more)
holding torque than the bottom. In real life it
is more like 55% to 60% more holding torque.

Yes the bottom system uses half the power. The
problem is that one field is collapsing at the
time you are making the next field. This will
be much worse at higher speeds for jumping
(losing position). The top system always has
one field at full magnetic strength when the
other is collapsed/rebuilt. This may be 3x more
torque at higher speeds.

You may find that you can reduce the current
to the coils and run two coils on. This may
give same power usage but better performance.
:o)
-Roman

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2001\04\26@061110 by Peter L. Peres

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The difference will show in slow mode. Try to set a very slow speed and
see what gives. There should be appreciable vibration in the motor running
the simple sequence.

Peter

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2001\04\26@062721 by Bob Ammerman

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Roman,

Would it make any sense to use

> > A -A / A -B / B -B / B -A

at higher speeds, but then use:

> > A / B / -A / -B

when running slower?

Bob Ammerman
RAm Systems
(contract development of high performance, high function, low-level
software)

{Original Message removed}

2001\04\26@071530 by Roman Black

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Bob Ammerman wrote:
>
> Roman,
>
> Would it make any sense to use
>
> > > A -A / A -B / B -B / B -A
>
> at higher speeds, but then use:
>
> > > A / B / -A / -B
>
> when running slower?


Absolutely, this also has another benefit mentioned
in "Jones" that the resonance speeds are different
and changing modes can be good for accelerating
through resonance problems.

The more common system is to use 2-coils on
when running and switch to 1-coil on for stationary.

A preferred system is to use chopper current drive
to the coils, this uses minimum current from the
PSU in holding and low speeds and brings in more
power at higher speeds to compensate for motor
inductance (copper) losses. There are a lot of cheap
one-chip stepper chop drivers now, for smaller <2A
motors anyway. :o)
-Roman

PS. The 2-coil on is properly shown as:
A+ B+, A+ B-, A- B+, A- B-

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2001\04\27@211429 by alshinn

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Content-Type: text/plain; charset=us-ascii
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Subject: Re: [OT]: Stepper motor sequence question


> Joan Ilari wrote:
>
> > I have built a 3 wheel rover powered by two unipolar 4 phase
> > stepper motors (one wheel is free). Each motor is controlled
> > (of course!) by a PIC. According to the motor datasheet,
> > the motor stepping sequence should be :
> >
> > A -A / A -B / B -B / B -A
> >

This cannot be right!
A -A, and B -B are both null.
More like A B / A -B / -A -B / -A B
here is a diagram:

     A
 -B     B
    -A

Go CCW in above diagram with 2 phases always on, for CW it's
A B / -A B / -A -B / A -B

Sorry if this is too pedantic!
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