--- In
Homebrew_PCBs@yahoogroups.com, "mycroft2152" <mycroft2152y@...>
wrote:
>
> Since we are all eagerly anticipating the machine photos, how about a
> little info on the electronics to whet out appetites.
>
> Myc
That's easy.
using wires and connectors, the bits and bobs are connected to each
other using Ben Franklins discovery of St. Elmo's Fire or maybe
slightly more correctly the harnessing of it.
With copper and tin, solder and flux, electricity is directed thru
paths and across depletion regions and even thru carbon !
I know many of you would like the details, so here it is....
Starting with some gallium and arsenic a voltage is passed, that runs
into the black box and from there magic happens.
That magic extends to end switches on each end of each axis, (6) along
with HOME switches on each axis (1 per), all controlled by one master
Emergency stop switch that also substitutes as a master-ON switch.
In another set of conductors, other magic happens. pulses are
transfered from digital bits to electroncal bits and then into motion.
these pulses create a pattern that control the movements of 3 separate
motors. each motor is controlled independently and with a precise
driver so that each pulse represents one specific movement in the axis
of which it controls.
The 1/4-20 leadscrews are connected directly to a stepper motor that
has an natural or full step movement of 200 steps per revolution.
mathematically, this results in 4,000 steps per inch in a full step
mode. One can calculate how a half step mode would yield 8,000 steps
per inch, or a 1/4 step mode would yield 16,000 steps per inch and so on.
For those who have a passing interest in the distance a 'step' might
be, at 4,000 steps per inch, each step would be 0.00025 inches or 1/4
of a mil. For those who prefer the metric system, that would be
0.00635 mm.
Power comes from a generating plant many miles from your location and
travels, uninterrupted, in a sinusoidal pattern called an AC wave
form. Our black box takes that AC wave and converts it into a 24
volt, 10 amp output. From there it takes a simple bridge to the DC
side and with the aid of some Aluminum Electrolytic material, is
turned into a much refined direct current. Interestingly, this also
simultaneously decreases and increases the voltage. First a slight
decrease of about 1 volt to get up and over the bridge, and then a
whopping 1.4x increase to yield a robust 33 volts to be used to power
the motors. Sadly, our endevours have not revealed the free lunch, so
that 10 amps on the primary side is reduced to about 7 amps on the DC
side.
Motor control is by means of a microstepping driver that can be set by
the user for full step, 1/2 step, 1/4 step, 1/8 step and even 1/16
step. All by some very simple jumper settings. nice !
We include the requisite red, ON light to indicate that power is
present along with a slightly audible hiss from the motors that
indicates the motors are being powered.
Motor power is still a little bit of a consideration. A PCB could be
etched with a 50 oz-in motor, although that is on the light side for
the capability of the machine, especially if one wanted to cut hard
woods and some dense plastics.
On the flip side, 200 oz-in is so robust that small carbide cutters
are in danger of breaking.
This is an area we do hope to get a lot of feed-back. just what
materials are being cut and how well the motors perform.
I hope I've answered some of your questions.
But, I think that any further discussion is best done on the FireBall
group, as this is really off-topic for this group, and although the
members have been very patient and courteous about this topic, I hate
to take advantage.
http://groups.yahoo.com/group/Fireball-CNC/Dave