Re: Geckodrive

To "keep a motor turning no matter what" is clearly impossible; it
requires infinite power from the motor. Nice mental picture though.:-)

Slowing down under load is a better option than the alternative;
having the motor skip steps, desynchronize or fault-out. That is the
practical definition of "stalling".

Mariss





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

>
> Mariss, this isn't making any sense, but I think it has to do with
> what you call a stall and what I call a stall.
>
> To me, a motor is stalled when it no longer rotates. Are you

saying

> that your GREX device will keep that motor moving no matter what?
>
> Now unless you have magic powers, this isn't possible. Which makes
> me think that your interpretation of stall is different than mine.
>
> Based on your description below, it appears as though the drive

will

> slow down the velocity in hopes that the greater torque at low

speed

> will overcome the load and allow the motor to rotate again.
> However, at some point, there will be a load in excess of what the
> drive/motor can overcome - resulting in a stalled (Stopped) motor.
> Does the GREX then fault or what is planned for this condition?
>
> Thanks
>
> Chris
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> <mariss92705@> wrote:
> >
> > No, the motor does not stall. It is prevented from doing that by
> > monitoring the lag angle and decelerating the rotating magnetic
> field
> > to prevent it from getting more than 1.8 degrees ahead of the
> rotor.
> >
> > The net effect is the motor slows down under heavy load. As it
> does,
> > more torque is available as speed drops until a "balance point"

is

> > found where available torque equals load torque.
> >
> > Relieve the load torque and the motor accelerates until a new
> balance
> > point is found.
> >
> > The lead/lag angle register is analogous to the position error
> summing
> > node in a classic servo. A step pulse increments this register,
> the
> > encoder count decrements it. The contents of this register is
> input to
> > a PID algorithm; the PID algorithm output then modifies the step
> pulse
> > rate to keep the summing node at a desired constant value.
> >
> > The lead/lag register also is used to increase the
> motor's "stiffness".
> >
> > An open-loop step motor has +/- 1.8 degrees of stiffness. In

fact,

> a
> > step motor only delivers its rated holding torque when its shaft
> is
> > displaced 1.8 degrees from its no-load position. The servoed
> response
> > is to "step into" the load, canceling this error. A 500-line
> encoder
> > gives a 10-fold increase in stiffness over an open-loop step

motor.

> >
> >
> > Mariss
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "lcdpublishing"
> > <lcdpublishing@> wrote:
> > >
> > > Okay, so the motor still stalls like any other stepper system.
> > > However, it tolerates the stall and provides feedback to the
> > > controlling software which would allow for a recovery if in

fact

> the
> > > problem causing the stall is self-correcting?
> > >
> > > It sounds neat, yet impossible at the same time. Either way,

it

> > > sounds like it has the potential of allowing higher speed
> performance
> > > from stepper systems. Perhaps I should look at this as if it
> were in
> > > an adaptive control system and it would make more sense.
> > >
> > > Sounds cool guys.
> > >
> >
>