Re: [CAD_CAM_EDM_DRO] Aaah! (Magically Moving Steppers)

In a message dated 12/28/2002 5:32:39 PM Central Standard Time,
abbylynx@... writes:

> Aaah! I'm thinking this is due to induced mains
> hum throwing the dir/step pins. Any advice?
>
> My system is a little limited still, so it's basically:
>
> Xylotex driver board
> Switched Mode PC power supply (12V driving the steppers)

Whew! Abby, surely Mariss will have more erudite advice for you, but
essentially, your "PC Power Supply" is probably the source of your problem!
A "switcher" is NOT the kind of supply, particularly at only 12 VDC, for
driving steppers! You do NOT need a stabilized ("regulated", here in the
USA) supply, and you want at least 24 VDC "unreg".

I don't know about the details of the Xylotex driver boards, but I downloaded
one the other night for SOME firm I don't recall, now, and it had NO
opto-isolator inputs---the Step/Direction inputs were 5 V. logic direct to
74HCnnn inputs, and, while 'HC' is very noise-immune compared to other logic
families, that is simply INVITING nebulous "where did THAT come from?" inputs
like you are experiencing!

Build, steal, purchase, or borrow a 24-36 V. supply that consists SIMPLY of a
"mains transformer", a bridge-rectifier (or four suitably-large silicon
rectifier diodes connected properly), and a good-sized electrolytic filter
cap. (I think the one you say you have will do fine). Use suitably-large
copper wires, and dress the "power lines", especially those to the motors, as
far from any "logic input lines" as you can, and if they must cross, do so at
right angles, not laying parallel for a few inches! Uh, centimeters!

Check that the 5 VDC lines that run around on the PC-boards of your
stepper-driver(s) have more than one or two 0.1 uF bypass-capacitors from +5
to common ("ground" or negative). If the 5 VDC "logic supply" is no more
than a 7805 type regulator which takes "motor voltage" and drops/regulates it
to +5 V., make sure there is a suitably sized 1N4001 or 1N5401 type diode in
series with the "incoming unreg. +ve" to that regulator-IC, and that there is
then a generous electrolytic from that "+in" diode's anode, to ground, of 470
uF or so.

On my last "stepper CNC machine", I used shielded ("screened" in UK, I
believe?) multiconductor cable to the motors. I also did several other
"just-in-case" tricks, such as mentioned above, etc., so I don't know if any
ONE of those things was the most important detail, but I DO know that this
new CNC machine has NEVER any missed or "gained" steps from no discernable
source, as do my previous still-in-use machines, from time to time!

Jan Rowland


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