Re: fickle y-axis

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