Re: Servo Hum (Was: Two Q's...)

Hi,

A badly tuned servo can break out into oscillation and rapidly
overheat the motor. Just short of that, it may "hum" for a second or
so after any direction or load change.

I don't think that is what's happening here though. This could be the
result of poorly spaced step pulses. The motor faithfully tries to
follow them; the resultant acceleration / deceleration causes the hum
you hear. The tipoff is the abrupt change from no hum to hum at a
certain speed.

I don't know your CPU speed. If it is slow, you may wish to try it
again with a faster PC if you have one.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "jbordens" <jake@a...> wrote:
> > If these motors are sitting loose on the bench you may just be
> hearing
> > some standing wave sort of rattle. This can happen with loose
> motors
> > that have very low inertial loads.
>
> I think this might be the case. I tried backing off on the gain
but
> this didn't reduce the motor noise. In fact, reducing the
dampening
> actually had more of an effect on the noise. With reduced
> dampening, I had to reduce the gain, almost to the lowest setting,
> which is not really good since I could stop the motor with my
> fingers and cause a fault condition with the gain so low.
>
> Bascailly, the hum starts at a specific RPM (almost like a switch,
> one second quiet, and the next humming). I could make the hum
start
> at a lower RPM by loading the motor with my fingers.
>
> For reference, gain is set to just past 50% and the dampening set a
> little further than that on my gecko.
>
> Even with the noise, things work fine, but I'll know more once I
> strap them to the mill (if it will ever get off backorder and get
> here already).
>
> For reference, can mistuning the servodrive result in a stituation
> that will damage the motor or the servodrive itself?
>
> As always, thanks again to everyone,
> Jake
>
>
> --- In CAD_CAM_EDM_DRO@y..., Ray Henry <rehenry@u...> wrote:
> >
> > Oops. Input and output scale are the number of pulses per unit
> distance.
> > They are not a measure of the gain of the axis. Axis gain (P) is
> > disabled with steppermod so that will not help you a bit.
> >
> > With your slow pc steppermod is the one to use. If you set the
> number of
> > pulses per unit and max velocity to high, steppermod will cause
> your pc
> > to crash or be really erratic. Short of that you should be okay.
> >
> > If these motors are sitting loose on the bench you may just be
> hearing
> > some standing wave sort of rattle. This can happen with loose
> motors
> > that have very low inertial loads.
> >
> > HTH
> >
> > Ray
> >
> > BTW -- Freqmod does not use external feedback but it does use the
> tuning
> > parameters P -> FF2. Smdromod does use encoder feedback from the
> > Kulaga/Mauch ISA board.
> >
> >
> >
> > On Friday 09 August 2002 10:00 am, you wrote:
> > > Message: 9
> > >    Date: Fri, 09 Aug 2002 10:31:59 -0000
> > >    From: "jbordens" <jake@a...>
> > > Subject: Re: Two Q's: Servo Hum and FreqMod issues
> > >
> > > Norm,
> > >
> > > Hmm, my output/input scale is already pretty high (20000).
> > > StepperMod is working well for me, so I can stick to it. ;)
> > > I just thought that FreqMod's behavor was a bit odd.  I suspect
> its
> > > looking for a closed loop which just isn't there, but as far as
I
> > > can tell, my settings are right.
> > >
> > > Mariss,
> > >
> > > I'll play with my gain a bit.  I guess when I tuned them my
pulse
> > > generator wasn't putting out enough pulses to really get the
> motor
> > > spinning fast enough to hum/rumble.  Now that I'm hooked to real
> > > software, I get the hum.