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

Jake,

Thanks for the kind words.

1. It's what you would call a "weak output". My problem in designing
this drive was sort of embarrasing; there weren't enough terminal
connections. Properly, the FAULT should have been an output and the
RESET should have been a seperate input. Rather it is both; primarily
a fault output which can be overpowered by a reset input. In your
case, I would connect it to an input on your PIC and also to a tri-
statable output. Read the input, then decide if you want to enable
the output.

2. The 6-pin header is there primarily for OEM customers. When
shorted, the top pair diables the "anti-dither" circuit, the middle
pair decreases the differential time constant by an order of
magnitude primarily for motors less than 1" in dia. and the bottom
pair inverts the default motor direction.

Our testing setup is a little simpler than you may imagine. The
trimots are set to the default position (shipping default). The drive
plugs into a test stand that has 12 spring loaded pins that match the
connector (pogo pins). Doug Yeager's CNCpro then drives a 2kW test
motor attached to a 1" / turn leadscrew that carries 15 lbs of lead
as a load on the slide. The drive must accelerate / decelerate the
load 5 times at 5G to a speed that requires 1kW to accomplish. This
is done at 100VDC and 20A. Drives that pass, ship; drives that don't
get careful scrutiny and rework. Most make it. Some don't.

Mariss

--- In CAD_CAM_EDM_DRO@y..., "jbordens" <jake@a...> wrote:
> Thanks Mariss,
>
> I do have a faster machine available, and I'll give that a go and
> report back here to let you know. Thanks again. You're the best.
>
> To nonrelated questions, if I may:
>
> #1 - Is the err/res pin tristated? The docs don't say specifically
> but I'd like to hook the err/res pin up to a tristate pin on a
PIC.
> I'm looking to monitor/set the err/res pin from a small PIC thats
> part of my Estop circuit.
>
> And #2 - I asked this in an earlier post, but I'll ask again. What
> is the 6 pin header near the test points for? Do you guys have a
> test harness that hooks there?
>
> The reason I ask is that I'd really like to somehow be able to hook
> up to the test points through that small hole there in the case.
> I'm wondering if I could biuld some sort of connector through the
> hole in the case that would connect to the test points (or maybe to
> the 6-pin header?) ;)
>
> thanks again guys. And thanks Mariss. I'll try a faster PC. ;)
>
> Jake
>
> --- In CAD_CAM_EDM_DRO@y..., "mariss92705" <mariss92705@y...> wrote:
> > 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.