Re: fickle y-axis

Hi all,

To make it a little clearer, N for the rotor's north pole, S for the
stator's South pole. Cycle start with rotor's north pole at A2


A1-B-A2-B-A3-B-A4-B-A5-B
------N

..........S
A1-B-A2-B-A3-B-A4-B-A5-B
----------N

...............S
A1-B-A2-B-A3-B-A4-B-A5-B
---------------N

So even with B non-functional, A3, A4 strong enough to attract
rotor's north pole to jump past B and move to A3, then to A4, say, in
a clockwise direction......

Let's say, Cycle stop and start again with rotor's north at A4.

.....................S
A1-B-A2-B-A3-B-A4-B-A5-B
---------------N?

How would a missing B phase cause N to rotate in a counter-clockwise
direction?

.....................S
A1-B-A2-B-A3-B-A4-B-A5-B
----------N?

Where would momentum figure in this case? I just sense something
still lacking in my understanding of stepper motor's working and hope
someone will fill it in.

Thanks.

Peter


--- In CAD_CAM_EDM_DRO@yahoogroups.com, "forumtvm" <forumtvm@y...>
wrote:

> Thanks Jeff,
>
> Very clearly explained.
>
> A1-B-A2-B-A3-B-A4-B-A5-B
> ------X--------------
>
> A1-B-A2-B-A3-B-A4-B-A5-B
> -----------X----------
>
> A1-B-A2-B-A3-B-A4-B-A5-B
> ----------------X------
>
> Momentum causes rotor to bypass B and fly all the way to the next A
> coil. Just a little bit more for complete understanding. Starting
> from A2, How would starting a cycle cause the rotor X to go to A1
> instead?
>
> Thanks
>
> Peter
>
>
>
>
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "jeffalanp" <xylotex@h...>
> wrote:
> > Hi Peter,
> > Why a stepper can turn with only one phase hooked up.
> > Have you ever seen those old cartoons where two guys (A & B)

are

> > on the railroad tracks with one of those hand pump types of

cars?

> > The two take turns pushing down on the lever, first A pushes down
> > (while B's handle goes up), then the B pushes down (while A's
> handle
> > goes up). The two phase of your stepper motor are kind of like
> that
> > (in full step mode). Now if one if the people (B for example),
> isn't
> > there, you'll have half the power, but as long as A's handle

wasn't

> > all of the way down, he can start some motion by pushing down on
> his
> > handle. If he pushes enough so that his handle, after reaching

the

> > bottom, will cycle all of the way to the top, he can start a full
> > cycle by pushing down again. As long as each down stroke

provides

> > enough power so that momentum will carry the handle back to the
> top,
> > he can continue pushing, and moving the car. Your stepper can

move

> > similarly, as long as there is enough momentum to get the rotor

to

> > the next cycle.
> >
> > The direction your stepper takes with only a single phase

attached

> > will be pretty much arbitrary though. (If you've ever seen an

old

> > foot-powered treddle sewing machine, the pricnciple is also
> > similar).
> >
> > I hope that helps a little.
> >
> > Jeff
> > http://www.xylotex.com
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "forumtvm"

<forumtvm@y...>

> > wrote:
> > > Hi,
> > >
> > > Did some detective work - tried swapping motor cables around.
> > Turned
> > > out that the problem followed the "y-axis" cable. One of the

wire

> > was
> > > loose, in fact, eventually broked loose from the soldered pin.
> > > Changing to a new cable solved the problem.
> > >
> > > However, I am puzzled as to how a bad cable can lead to erratic
> > > behaviour, that is when a movement in the positive direction is
> > > commanded, sometimes it move in the positive direction, and
> > sometimes
> > > in the negative. How would a motor behave if, say phase A wires
> are
> > > OK but phase B connection is bad/broken. Would this cause the
> motor
> > > to move in the opposite direction to that commanded?
> > >
> > > Am more interested in understanding the problem than in getting
> the
> > > problem solved. Hope someone smarter than me will explain.
> > >
> > > Puzzled.
> > >
> > >
> > >
> > > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "forumtvm"
> <forumtvm@y...>
> > > wrote:
> > > > Hi,
> > > >
> > > > Using DeskWinNC, Camtronics 2A driver, 33VDC power supply, I
> was
> > > > getting only 16-18 ipm previously.
> > > >
> > > > Happy to report that after changing to a Pentium 4 and

DeskCNC

> > > (with
> > > > the same old controller board) I managed to squeeze 35 ipm

from

> > the
> > > x-
> > > > axis before stalling. For the z-axis, I could get 17 ipm.
> > > >
> > > > However, the y-axis seem to be acting up. At one stage, I

could

> > > only
> > > > get it to make noise without any movement. After powering

off,

> > > trying
> > > > another day, it was OK again. Now the y-axis can't seem to

make

> > up
> > > > its mind whether to move forward or backward. In MDI
> > > > G91 G01 Y0.1 F10
> > > > it is supposed to move forward (same direction) each time it

is

> > > > activated. But what is happening is, sometimes it move

forward,

> > > other
> > > > times it move backward.
> > > >
> > > > DeskCNC uses a serial cable from PC to controller board, and
> > > parallel
> > > > cable from controller board to driver. So I try to see if I

can

> > > > isolate the problem. I switched to TurboCNC which uses a
> parallel
> > > > cable direct from PC to driver. Same problem.
> > > >
> > > > What could be the possible cause? Where should I start

looking

> to
> > > > solve the problem?
> > > >
> > > >
> > > > Looks like a lot more work to get a consistent dependable
> system
> > > > going.
> > > > Thanks
> > > >
> > > > Peter