Re: Geckodrive

Well, it's a motor physics thing. Unlike steppers, servomotors have a
torque limit independent of speed. Nothing is gained by slowing the
motor down; if the continuous rated torque 250 in-oz, it's the same
at 3,000 RPM and at 1 RPM. The only benefit would be if the work-load
decreases with speed.

In a word, if the G100 can monitor the servomotor encoder, it can
adaptively slow the servo down if the following error exceeds a set
threshold.

If the overload torque is speed independent (lifting a weight against
gravity), then the consequence would be a speed reduction to zero or
reversed direction motion.

An apt analogy with which to view step motors is to imagine a
constant-speed motor attached to an infinitely-variable gearbox. The
step pulse frequency modifies the gearbox reduction ratio; double the
ratio and you get half the speed at twice the torque, etc.

You don't get that with servomotors.

Finally, give the poor step motor a break.:-) It too is a mighty
servomotor deserving of respect when run closed-loop. What is your
servomotor outside a closed-loop? Just an ordinary AC or DC utility
motor.

Mariss

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

>
> So Mariss, Is your G100 going to have an advantage using it
> with a servo system? or is it primarily going to be for
> use with steppers. There are a lot of servo guys out there
> that need the G100 advantage in there servo systems.
> What can a G100 do for a servo system?
>
> Scott
>
>
>
>
>
> --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Mariss Freimanis"
> <mariss92705@> wrote:
> >
> > A truly unstallable motor would have to deliver infinite power.:-)
> >
> > I call this "the unstallable step motor project" because of its
> > practical implications. An open-loop step motor has only two

options,

> > run or stall. If stalls while work is being done then more likely
> > than not that work will be ruined.
> >
> > This is also true for ordinary servo drives. If overloaded, they
> > develop a following error; if the following error is large

enough,

> > the drive faults-out and the motor stops. Same result.
> >
> > The "unstallable" step motor will just slow down when overloaded.

The

> > G100 will slow the other axis motors down by the same ratio and

your

> > work will be unaffected. You may not even notice it until after

you

> > oil your machine.:-)
> >
> > By this definition the motor is "unstallable" in practical terms.
> >
> >
> > Mariss
> >
> >
> > --- In CAD_CAM_EDM_DRO@yahoogroups.com, "Graham Stabler" <eexgs@>
> > wrote:
> > >
> > >
> > > It seems there is some confusion because it is not unstallable
> > because
> > > the system can beat any load and carry on regardless rather it

rolls

> > > with the punches. If something loads the motor such that it

cannot

> > > carry on at its current speed it slows to get some more

torque. At

> > > the limit I guess it will stop but it won't be trying to go

anywhere

> > > either!
> > >
> > > I suppose you could say the definition of a stall is for a

motor to

> > be
> > > trying to move when it can't. The unstallable drive knows when

it

> > > needs to slow down to keep moving and ultimately when to give

up :)

> > >
> > > Jack, the resonant type stall dues to the mid band stuff it not

the

> > > kind of stalling that is being refered to as far as I can

tell. I

> > > also beleive that the geckodrives deal with the mid band

resonances

> > > already.
> > >
> > > Graham
> > >
> >
>