Pre-raquisite Software Skill for operating the BEAST

Building the CNC Router was a stressful but fulfilling experience. Inflated ego was the direct product of this memorable journey. BUT that is only the starting line of my CNC endeavour. Now that I have a machine at my disposal, I need to learn up how to drive this machine to churn out those beautiful artifact like we seen in the net.


In retrospect, running the machine is easy, but that is only after you actually operate the machine...

I totally over estimated my learning capacity, & underestimated the complexity of the software involvement in running a CNC machine. After over a month of tinkering with running the machine & many software packages, I come to this overly generalised summery.
You need a Drawing to convert to G-code, feed the G-code to the Motion Controller. To cut properly, one need to know the cutting tool characteristics, material properties & some machining procedure knowledge.


Drawings
To make something with or without CNC machines, we need to provide specific specifications of what to do, so coming up with a drawing is the first step.
From my understanding, we can use 2 types of drawing files, namely Raster & Vector.
In raster, examples are bitmap such as jpg, png etc. With this, the cutter will transverse the whole area covered by the file, this is how most 3D cutting is done. With Vector file, the cutter only travels along the path where the cutting is required, saving lots of time. this is how profile cutting & 2.5D are done.


Drawing software
With different cutting strategies different software are used. In vector files, we direct the cutter in straight lines to cut the profile or contours, leaving the other space alone. In raster file, the cutter will transverse every mm of the file... example of raster files are bitmap. & the generally accepted vector file format is .DXF, other formats are SVG, AI, STL... etc etc
I'm fortunate enough to have worked with AutoCad in my junior career life & residue memory helps a lot when relearning. This is my preference for 2D & 3D rendering but there are others such as SolidWorks. You can also use CoralDraw, Win Paint, Adobe Inventor, SketchUp Pro,.... Open source CAD drawing are not quite up to the fee software but I find Blender is a promising, still crude but its getting somewhere.
I also learn that one doesn't need to draw a drawing from scratch everytime, especially when we are dealing with ornamental & art craft... We can "convert" raster files to vector files by tracing bitmap. I downloaded the open source INKSCAPE software which can do many capabilities of fee software such as the Coraldraw & Adobe AI.

G-code
One can write G-code from scratch if they feel they are up to it, BUT I'm too lazy for that... CAMBAM, UCANCAM, SHEETCAM, LAZYCAM... a whole library of CAM software which can translate vector file into G-code. I evenetually ended up with VCarve Pro for 2D & 2.5D works & Cut3D for 3D works..

At the end of the day, depending on requirement, all common or not so common software packages works, the difference are in the learning curve & the ingenuity of the user to utilise the available capabilities of each. Its a compromise of $, time & requirement.

The CNC Electronics & Electrical Department Happening

I have a confession to make....

I finally did it! I killed ALL the board in my control panel!!! There goes the PMDX-122 breakout board & the Atom MOBO!!! :(

It all happend in that thundering night, wind howling... fist size rain drop pouring.... blue flashing thunder... door banging....... Err.... nothing of that sort, ;p

Over the X'mas holidays, I proceed to wire up the control panel. Individually,  the magnetic coil contactor, E-stop circuit worked out the Mobo worked fine, BUT they don't jive with each other, ...

Wire all the components, press the start button, hear that satisfying "thump" made by the magnectic coil contactor, and a few blink of the monitor & everything went black-out.... Dead! Mati! Kong! & I didn't have the pleasure to seeing smoke!!!

With a puntured ego & coffer, I went back to search for another board as the return shipping charges to send the dead BOB back to the maker is plainly irrational.

Undetered by this set back, I (again) dive into the vast ocean of information- the internet & picked up this SINYU 5-Axis Interface Board. from the ebay.

This chunk of populated electronic component PCB features a Manual Jog function by connecting a home made joy pad, the circuit for the joy pad is given in the manual.
It has 2 Relays which I can switch on larger Magnetic coil relays for auxillary equipment.
Charge pump featured
Unique 10-wire ribbon cable terminal for connection to the Stepper Driver. I have a choice to configure the board for 5 stepper driver connection or 4.
4 sets of powered 3-port terminal with 12Vdc VCC ready for home/limit proximity switch connection.
Takes 9Vac as power which is easy to implement.

AND it is $$$ friendly too.

As for the Mobo, a replacement were sorte.


Total damage?
RM836  = USD 245 = EUR175 = GBP151= ZAR1,860 = 11,360 rupee = HKD 1,907........

ooooooooouuuuuuuccccchhhhhhhh........

 ##PS,
Read the small print

So..... Please support this blog by clicking on the ads.... every cent counts.....

;)

The stuff that makes up a PSU

In the previous post, I choose a E-I Core, 300VA, Secondary winding 48Vac. which should have 66.5Vdc 4.5A

I happened to have a 540VA, Double bobbin, 36Vac E-I core tranny collecting dust in my junk box. It says 36V, 15A, So I approach a friend to add a few more coils on the secondary and I now I have a 48Vac, 11.25A tranny for the job.











Now for the Capacitor,

Voltage rating,
It is safe to have a 1.5x safety factor over the expected rated peak,
So, 66.5 x 1.5 = 99.75V
so a 100V rating Cap will do just fine.

Another safe formular to guide us along,
C = (80,000 * IMax. total) / Vdc (microFarad)
C= 80,000*(4*4)/66.5 = 19,248.12 uF

Capacitors don't come in this exact size
This is what I found off the shelve, a 22,000uf, 100Vdc Screw terminal electrolytic capacitor.




Ractifier is easy,
minimum Voltage rating is 100V, minimum current rating is 4x4x1.5=24Amp but we know from the tranny selection 2/3 of that would be enough so 2/3 of 24 is 16Amp

I got this KBPS2504,250V & 25A. metal casing which is good for heat dissipation. when I mount it to any metal plate.

Next, is Wire selection, We know the motor rating is 4A max, but nominal operating current will be much less. Anyway,  14 gauge AWG wires will do 4amp nicely & since they are easy to get I used some 8Awg (easily 15Amp) speaker cables for the job. all I need now is some crimping pins, some soldering work....


A quick wiring work yielded this

Value Engineering the Stepper Motor PSU

The word "DESIGN" had been over rated & over used... Everyone in the advertisement design something... I prefer to use "SELECTION".  e.g. select a few different color clothing & you have a in-store fashion designer... do you "design" a 200hp engine for your car or you select? Do you select chopstick over fork & Knife or design... Can anyone claim the credit of designing a wheel? but we keep seeing this " we design of the wheel to xxxx, yyyy......."

Enough of my ranting, lets get back to the Stepper motor Selection.

Like everything else, we must know what we need before we can conduct a proper selection.

Stepper motor system consist of a stepper motor and a Stepper motor driver or amplifier.

Stepper motors takes in high current pulses which the motor driver made by chopping a DC current with respect to the instruction from the Brain. So we need to prepare a DC power supply for the Stepper motor system.

We starts with the Voltage rating,,

There is a straight forward & safe formular commonly used in the industry,
V=32 x SQRT(Coil Inductance in mH)
you can go higher but just watch out for the motor temperature.

EG,
My coil is 3.5mH
Vdc=60V

Secondary Voltage of the Transformer
Vsec=(60V+1.4V(voltage loss of rectifier))/sqrt(2)=43.4V
common transformer off the shelf are, 6V, 9V, 12V, 24V, 36V, 48V.
So, 48V is my choice. this will give
48xsqrt(2) -1.4=66Vdc#


Current rating
Most will follow the convensional wisedom and add up all the max.current rating of the motors & call that the PSU's current rating.... Nothing wrong when its a small system with total 6 Amp of current, but with a full size machine, the motor max rating of each motor can be 7~8 Amps... if there are 4 motors, the DC is 50V, that will require a 1400VA~1600VA about 2hp!!! That will be huge, heavy & expensive!

One must understand that we normally don't use up all the power the motor can do, i.e. the rated power... the motor will only produce "enough" power to move whatever they we designed to do, so it is all too common to see motor rated for 3kw only work 0.5kw with plenty of headroom.

With that in mind, lets do some "value engineering",
We know
we will never run the motor to the max limit because its a bad design practice. we know all the motors don't run at the same time...
Now we need to determine how much current the motor need to move the burden it was entrusted with. again there are more then one way to find the number,
By mathematics model, culculate the weight, inertia, moment... etc of the overall mechanism & find out the torque and hence the power required... I always keep this option last... even if I can, why should I go throught the whole trouble?
By experiment, build the machine, measure the torque required, this is always a good option, but I need to build the machine first....
Empirically, we can measure the current drawn by motors in similar machines.

I went for the empirical method, many reported to run on 300VA without risk of over heating and burning transformers, Even though they have a different voltage rating from mine, 300VA is the figure I need to know.

VA is a very close equivalent to Watt, VA is derive from multiplying the Voltage and the Current, this current is the resultant current and the current of W is the reactance current, but they are very close in number in this case.


Regulated or unregulated Power supply,
Again, common wisdom will pick regulated power supply, but really it is the worst choice for this application.

The nature of the stepper motor operation is such, when stop, they draw near zero current and when they move, they need current immediately or risk loosing steps,

Regulators are not famous for fast response, to ensure they meet the motor demand, they have to have the full power ready all the time, but the machines hardly use up the the max as we know by now, that extra power will turn into heat and wasted...

As for Unregulated power supply, they only give when the load ask and it does have a capacitor to act as a ripple filter & double as a reservoir.

SO since SMPS is normally regulated & the unregulated one are not good in drastic load demand, it is ruled out.

Transformers
There are few types of transformer core, The C-core, R-core, Toroidal & E-I core.
C-core & R-core are not as commonly available as the used to be and that leaves us with Toroidal and E-I core.
Toroidal Core is a more efficient transformer, but it is its efficiency that became its weakness in this application.
Toroidal response to suddent load demand extremely well, so well that it will burn itself when responding.
E-I core is less efficient magnetically, but because of this deficiency,  the hesitation acts as a buffer to protectects the transformers from burning its coil.

So, there you have it,
My best package selection is
Transformer :- 300VA E-I core transformer with a 48Vac secondary voltage
Rectifier :- Bridge rectifier with metal casing, rated over 100V & 25 amp
Capacitor :- 22,000uf @ 100V Capacitor based power supply.

This also turn out to be the cheapest & the least technological advance combination.