Re: Machine Setup

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Heidi Johnson <hjjohnson@...>
wrote:

>
> Thanks Les, The G100 is in the cards for sure, I'm kinda holding out

to see how this machine run's first before either jumping to servo's
or..?? [not sure.. might wait for the unstallable stepper thing if
this current design is good enough power wise] Is it possible to
somehow shield the parrallel cable? I was wondering if wrapping it in
that aluminized tape would do it or.. I can get my hands on actual
copper foil [ used in making electrical cable] which I could wrap
around the cable and then ground with the rest of my shielded cables?
Is this a no-no or..?? I'd really hate to have to get that long of a
mouse, VGA, and keyboard cable if I can help it :-) It'd be much
easier to just run two [ power and parrallel].. I've already know that
the easy route isn't always the best so.. I'll take the best route,
but.. you know where I'm coming from..


If you look at commercial machines they often put the drive
electronics close to the motors and then all you have to worry about
is feeding them the step and dir signals. Those are easier to amplify
or use differntial line drivers on (two signals on each driver) than
to try an run logic level signals all over creation. I used that
approach on my plasma table because I didn't want to deal with the
encoder signals (non-differential) coming back across acres of noise.
The Gecko's are mounted less than 6" from each motor and the only
thing that you have to try and feed remotely is the motor DC (easy)
and the step and direction signals. Using good buffers, shielded
pairs and the low impedence of the opto inputs makes this easier to
do. For extremely long runs a set of differential line drivers on the
step and direction signals would make it usable up to 200' or more.
It also eliminates a source of transmitted noise since the high
current PWM motor signals are at the motor and not 20' away with long
feeds. After having observed a lot of commercial and industrial
equipment and seeing the drive electronics almost always mounted close
to the motors it occured to me that maybe those engineers were on to
something! (:-)

Do not try to use video, mouse and keyboard extensions in an
environment with a lot of noise. It's bad enough with the
conventional 6' stuff. Hanging more antennas out there can only make
things worse. One of the better things you can do on longer cables is
to clamp on big ferrite filters on both ends. Several surplus
electronics sources have them for computer cables. All that being
said, cables longer than 15 feet for critical signals should be
avoided. The inner capacitance of the cable causes high frequency
signals (like the leading and falling edge of a square wave) to round
off. For things like switches and such it's no big deal but for drive
signals it's a killer.


Tom Caudle
North Texas

Http://www.CandCNC.com
"We just made CNC easier!"

Hardware for Home Shop CNC:
Low cost, powered/isolated, breakout card
AC and DC "Drive Saver" power controls
2nd Generation digital THC
Handheld Manual Pulse Generator (MPG)