Re: [CAD_CAM_EDM_DRO] First note-Help Mariss Help us with shielding???

Dear Brave Soul,

Tim Goldstein is correct about the 320's and 340's and although I am a penny
pincher, I always seem to find some way to do something different with
whatever I buy, sometime in its lifetime. So, for me, the $30.00 extra per
drive gives me some added flexibility that I am buying. It also allows me
to choose many different encoders. Sometimes I want to try some other
machine, and with the built in multiplier, I can experiment on
configurations. Of course, that is 30 * 3 or 90 bucks. It would not hurt
to try one 340 and 2 320's, just so that you had one around. I will not
drag this point out.

As far as the encoder noise is concerned, what a puzzling thing. We used a
foil shielded cable for the servo motor drive voltage, and a separate foil
shielded cable for the encoder signals, and kept them separate all the way.
We also put a .1 uf cap at the encoder end of the cable between +5 and gnd.
Cables around 10 feet from drives. We grounded the encoder cable (no
twisted pairs inside) at the drive end, and left the motor shield
disconnected. The drives faulted constantly. We cut the ground wire
connecting to the shield on the encoder cable, and it ran with only an
occasional fault. We grounded the servo motor drive cable and the faults
stopped. Never could see much on the scope in the way of noise. Before we
found success, we also built a little amplifier and put it right in the
cavity of the servo motor with the encoder. The amplifier was made with a
74HC04 (per Marris's advice). We paralleled three of the inverters for A
and three for encoder B signal. It still faulted every time until we
shielded the servo motor power cable. Jon Elson has pointed out to us that
this foil shielding will not last the life of the cable if the cable flexes
all the time. So, keep that in mind when you select a cable. If I have
dragged this out too long to keep up, the bottom line is that the only
configuration that works at this time is to have the servo motor drive cable
shielded, and leave the encoder cable unshielded. Don't ask me why. I
don't know. I would have thought it better to shield the encoder cable. If
we try to ground the encoder cable sheild, it faults out all the time.

Electrical noise has been a real pain for me in many projects I have worked
on.

----- Original Message -----
From: Tim Goldstein <timg@...>
To: <CAD_CAM_EDM_DRO@yahoogroups.com>
Sent: Friday, June 29, 2001 10:51 AM
Subject: RE: [CAD_CAM_EDM_DRO] First note-Help


> I will second the recommendation of going with Gecko G3X0 step and
direction
> servo drives if you have not purchased anything for steppers yet. While
Tom
> is suggesting G340's my preference is to go with G320 and select the
> encoders to give 6,000 - 10,000 steps per inch. The only difference
between
> the G320 and the G340 is the latter has an additional plug in board that
> allows you to "multiply" you incoming pulses to drive servo setups that
> require very high steps per second. Helps to take the stress off the
> computer, but you can accomplish the same thing by selecting appropriate
> encoder counts. The G320 is US$30.00 cheaper per axis that a G340. I have
> G320's on my Shoptask and am in the process of setting up Bridgett (a
> Bridgeport series II) with G320's. I love them and feel there is no
> comparison to a stepper.
>
> I would also give an endorsement for US Digital ( www.usdigital.com ).
Nice
> products, reasonable prices and super to deal with. For motors I have been
> very successful picking them up on E-bay.
>
>
> Tom,
> How did you avoid electrical noise interfering with the encoder? I seem to
> be having some problem with that and just got some National DS9638 &
DS9637
> differential driver and receivers to eliminate the problem. Regarding the
> 9638/9637 can any of you electronic gurus help me with a circuit diagram
to
> interface them with the encoders, the G320's, and an external power
supply?
> Don't want to tap the power off the G320 encoder power taps as I am sure
the
> current draw is beyond the Gecko spec.
>
> Tim
> [Denver, CO]
>
> > -----Original Message-----
> > I'll throw in my recommendation that you get some Gecko 340s
> > and find some
> > servo motors and skip the steppers, if you haven't already
> > started down that
> > road. The Geckos really only have two adjustments to make, Gain and
> > Damping, and you can tinker with them and get them running
> > pretty well. The
> > limit pot adjustment is no big deal. I think CNC pro is
> > very popular on
> > this list, and many others will suggest their favorite cad
> > /cam software.
> > Yesterday, I just finished retrofitting a series I Bridgeport
> > mill with the
> > Geckos, and I love them for their simplicity. US digital has
> > cheap encoders
> > too. Just watch out for electrical noise interfering with the encoder
> > wiring. Tim is also in the process of retrofitting a big
> > Bridgeport mill.
> > Get a catalog from US Digital on their encoder products.
> > Their encoders
> > will fit many shaft sizes.
> >
> > Others may suggest servo motor sources.
> >
> > Tom Eldredge
> > >
> > > Addresses:
> > > FAQ: http://www.ktmarketing.com/faq.html
> > > FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
> Addresses:
> FAQ: http://www.ktmarketing.com/faq.html
> FILES: http://groups.yahoo.com/group/CAD_CAM_EDM_DRO/files/
>
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