Re: [CAD_CAM_EDM_DRO] Stepper Motor steps and other questions

Russ: Good, proper questions! Some folks members here know more than I
do, but I will throw in MY 2¢ worth, anyway, as I have "been there, done
that":

> . . . leadscrews are 10 TPI. My questions are, does a stepper motor make
> one step for each input pulse?<<

Not exactly, but yes, sorta! The DRIVER CIRCUIT usually CAUSES the motor to
make one step for each STEP-input
pulse. An "input pulse" is just a 5 V. square-wave pulse, on/off. But a
"motor step" is caused by a polarity-change on
one of two windings in a stepper, the NEXT step being a like polarity-change
on the OTHER winding, etc.

> Can a computer output the pulses from the parallel port fast enough to

make it run at a rate of 2000 pulses a second?<<

Even an old '286 with a 5 mHz. clock can ouput up into the tens of kHz. from
the parallel port, with approp. programming.

> I will probably have to run windows NT as an operating system. I see that
> most stepper motors make 200 steps per revolution so I can calculate that.
> The nice thing about the DRT is Ieverything is relative. I don't need to
> know where the "bug" is, just make it move the correct direction and
> distance following ship movement. The bug is manually positioned initially
> and when it reaches the limits of travel. I don't know how much torque is
> required to turn the screw but without the gearing I don't expect too much.
> I am thinking of using nema 23 or 34 motors.<<

I suspect the machine you describe at the outset will need AT LEAST
good-sized NEMA-34 motors, preferably KML- series bipolar (which have much
more torque than "same size" unipolar "six-wire") Size-23 are big enough for
plotters!

I also don't quite understand the high voltage I have seen mentioned. I
was under the impression that the motors ran > on 5 or 12 volts,<<
Though some steppers actually have (approximately) "5 volt windings", and
a few very-special ones may have even higher voltage winding-ratings,
MOST have quite-low voltage winding-ratings FOR the current-ratings specifiec
for these same windings. Confusing to a non-electrical type, yes. But a
stepper has WINDINGS in a VERY magnetic environment, so there is TREMENDOUS
inductance and CURRENT. This can cause VERY slow "energize" and "decay"
times at those "rated, steady-state voltages". BUT, when a stepper's
windings are being PULSED on/off, the CURRENT will drop much lower, UNLESS
the VOLTAGE is made higher. This is where the DRIVER circuit's complexity
comes in. On "old fashioned" unipolar "L/R" motors, this is done via a
COMPROMISE with "ballast resistors" in series with the motor-windings and the
HIGHER-voltage power-supply. This "extra" voltage is "wasted" in those
resistors when the motor is still or running slowly. NOT efficient!
Present-day "bipolar chopper-drives" (like Gecko G210 or Superior Electric
2000 series) "put the high-current through, regardless of speed" (sorta),
and, to do so, require those "higher" voltage power-supplies. The Gecko
drives can go up to 80 VDC for motors that "want" only 2 or 3 VDC on their
windings! They keep the AVERAGE current through the motor-windings proper
via "chopping" the DC, and modulating the "duty-cycle" of the current! Nuff?
OK, I will stop.

although I would like to run the motors at 28 volts since I have those
supplies available.<<>

>

Just fine! The Gecko 210, for example, will put ONLY the set current through
your motor's windings (so long as you select the CORRECT "current-set
resistor" when installing them), and 28 VDC is sufficient for this size of a
machine, I think!

I hope this isn't too far off topic.<<

Not at all, I think! Lotsa luck! Jan Rowland




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