Re: Lost steps

By any chance are you using a full-step drive? The symptom you
describe is typical if your speed is low (less than 1 RPS)when
running a full step drive. The motor will have 2, possibly 3 severe
resonance speeds. For a size 23 motor they might be at 20, 40 and 80
full steps per second.

Is there a lot of vibration, like the motor would dance off the bench
if not held? Does the vibration become noticably less if the speed is
changed slightly? Then it is normal full-step drive behavior. Avoid
those speeds.

Other possibilites are bad connectors. Gently wiggle or tug on the
wires from both the motor and the PC and see if there is a repeat.
Check the DIRECTION input. A loose connection here could do that too.

Also check your drive's outputs with a scope if you have one. It is
possible to have a damaged phase output behave that way.

The least likely cause is a step motor. Bowling balls are easier to
break than step motors. You can check it by turning the motor shaft
with your fingers. The motor should be disconnected. Compare the
torque necessary to turn it to a similar, known-good motor. If it is
much higher then you may have an inter-winding short. Not likely
though.

The motor temp sounds normal if you deg F, it is very high if you
mean deg C.

Mariss

--- In CAD_CAM_EDM_DRO@egroups.com, Ozzie@h... wrote:
> Update:
> After quite a few hours of fiddling without much progress, except
to
> improve some wire connections, I decided to romove a motor and
watch
> it. I was amazed to see it not only stutter once in a while but
> sometimes take a backward step.
>
> Up until now I have wrapped the signal wires inside the cabinet
with
> aluminum foil and connected the foil to ground, reduced the
> acceleration in EMC, reduced the feed speed, and retested the
boards
> as the Camtronics direction instruct. I also moved the parallel
port
> cable away from all other wires.
>
> Is it possible my motors are bad? I don't know their history.
> Might I have them wired wrong? They seem to make 99% of their steps
> right.
>
> What else might help someone figure it out?
> The stutters are not at any particular part of the move. They vary
> fro
> one every third revolution to several a revolution. During an
hour's
> no load testing the motor gets quite warm, maybe 100 degrees.
>
> Anyone???
>
> Jerry
>
>
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@egroups.com, Joe Vicars <jvicars@c...> wrote:
> > True but the cost of precision is comming down. Precision
has
> two components, accuracy and repeatability. Machines in general
> > are becomming more repeatable (if not more accurate) and these
> machines are used to build other machines thus improving the overall
> > precision of what is available. The bell curve is getting
> narrower.
> Six sigma and all that.
> > Peace
> >
> > Terry Ackland wrote:
> >
> > > ---Ron,
> > > I have mill drill in my basement and the lead screw is all over
> the
> > > place. If I need to do anything fussy I have to set up an
> indicator
> > > because I cannot trust the dials.
> > > I can remember many years back working on a new Bridgeport with
> > > digital readout and expecting it to perform like a jig borer.
The
> > > first job sorted that notion out!
> > > You have to pay for precision and you cannot really expect it
from
> > > what most of us hobbyist are prepared to shell out for.
> > > Terry
> > >
> > > In CAD_CAM_EDM_DRO@egroups.com, Ron Ginger <ginger@s...> wrote:
> > > > Ozzie@h... wrote:
> > > > >
> > > > > In repeated attempts to determine the backlash on the axis,
I
> > > find
> > > no
> > > > > consistency in dial indicater readings. On the X axis I lose
> > > > > .002-.003" cumalatively in one direction. On the Y axis the
> > > readings
> > > > > are erratic with variations in the.002" area.
> > > >
> > > > Everyone else seems to be looking for electrical causes, Id
> look
> for
> > > > plain old mechanical ones. And this is exactly why I do not
> think
> > > > software compensation for backlash is worth it. You are
finding
> its
> > > > almost impossible to accurately measure the amount, so how
can
> the
> > > > software accurately compensate?
> > > >
> > > > Variations can come from wear in the screws, variation in
> friction
> > > from
> > > > move to move- chips in the way, etc. Try making the moves
under
> as
> > > > constant a load as possible- like while cutting a slot in some
> > > stock.
> > > >
> > > > The only solution to backlash is elimination! Ballscrews or
> Moglice.
> > > >
> > > > ron
> > >
> > >
> > >
> > > Welcome to CAD_CAM_EDM_DRO@e...,an unmoderated list for the
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