John, et al:
The good thing about linuxcnc is that is can accommodate a wide range of
user skill; from those who just want to make chips to those that want
to dig into the internals, to those that can actually write internals.
Ditto on the range of machines. Linuxcnc nee emc was tested on rather
good sized machines at Boeing, GM and probably others. I think we have a
few users that have machines in the 10 Kg region or more. I land
somewhat in the middle with my big machine being 4200 Kg. On the other
hand there are machines that one could pick up and walk out the door with.
Because linuxcnc is open source there are a variety of controls
available, steppers as well as servo, including the ability to use
rotary incremental encoders, glass scales, and resolvers.
Further history is here:
http://linuxcnc.org/docs/html/common/emc-history.html
The first system ran on a rather expensive VME bus system but things got
cheaper when STG (Servo to Go ( only $888 )) offered an isa bus card.
Nuff blithering: back to getting something done. ;-)
Dave
On 2/14/20 12:59 AM, John Dammeyer wrote:
-----Original Message-----
From: Chris Albertson [mailto:albertson.ch...@gmail.com]
Sent: February-13-20 9:51 AM
To: Enhanced Machine Controller (EMC)
Subject: Re: [Emc-users] Open source CNC architecture
Yes, you do need a special PC. This means a PC you use for Linux CNC and
not the one already on your desk.
I think that Chris made a lot of good points. Since I'm upgrading my mill to
CNC and using a dual boot PC and either LinuxCNC or MACH3 on WIN-XP/7 perhaps
can add a slightly different view point.
When I designed the E-Leadscrew Electronic Lead Screw controller the feedback
from the non-CNC people was that they wanted something more than just
electronic gearing (now commonly also called an ELS) but not something as
extensive as full CNC. So what exactly does that mean? For that matter what
does open source mean? Those are both really good questions.
I'll pass on the lathe description for now and address a milling machine.
I've managed to get along for a number of years with a DRO and power feed on
the X axis. Adding a 5C collect spin indexer and a small rotary table indexed
by my ELS I've found I have been able to create quite a few different things
without CNC. So why has it taken so long to convert to CNC when my JGRO based
CNC router ran MACH3 from the start. It's not like I'm afraid of it.
Quite simply for many milling (or lathe projects) that are one-of, the precise
feedback of a DRO on all three axis and power feed relieves the boredom to a
certain extent. But what would improve any mill is power feed on all three
axis along with the DRO. And the power feed, if augmented by begin/end
positions would allow all sorts of linear mill operations including peck
drilling and, with spindle feedback, like threading on a lathe, power tapping.
No G-Code based CNC code required. And unfortunately no I,J motion for arcs.
Although even those kinds of motions could be set up just as easy as
co-ordinated motion like the tapering I have on my ELS.
So now we're back to the question that Chris raised about a PC or a dedicated
embedded controller and relates to my first question above. LinuxCNC and the
PC worked because it used the parallel port, or if an add on card was added
closed loop servo control was possible. But at some point we cross the line
from a PC running the CNC software to the PC serving as the interface to custom
hardware with FPGAs and/or processors dealing with the motion control. So the
line has become blurry.
The costs, and they are always important, break down to the high powered
trajectory planner and user feedback, the actual motion signals and finally
the electrical interface often referred to as a Break Out Board. Some of the
ancillary hardware combines the BoB and the motion control into one package.
Other solutions use Ethernet to something that creates the motion signals
coupled to a BoB. And above both is the trajectory planning/control and user
interface.
But unless you use a parallel port that is part of the PC the reality is the
system has already been broken into a CNC controller of some sort that costs
between $100 and $300. If you decide to use a MESA Ethernet solution with
terminal strips and stepping engines etc. there is nothing in the rule book
that says that the user interface and trajectory planner has to be LinuxCNC.
And on the other side if you are using LinuxCNC if the HAL file loads an
equivalent to:
loadrt hm2_eth board_ip="192.168.1.121" config=" num_encoders=0 num_pwmgens=0
num_stepgens=5"
there's absolutely no reason the device with the above IP address has to be a
MESA product.
It could, in fact, just as easily look like the $300 CNC controllers with LCD
displays, buttons terminal strips etc. to connect to Servo or step motors etc.
And that $300 CNC controller might just have the equivalent to my ELS user
interface that lets you operate this mill as a manual mill with DRO, power feed
and some pre-programmed motion. So without the PC and LinuxCNC it's a
sophisticated manual mill. Power up the PC or tablet or whatever talks
Ethernet and LinuxCNC (or whatever user interface + trajectory planner) and you
have full CNC.
And that's where the second question perhaps might be answered. What exactly
is open source? In a way it's LinuxCNC but only a few guru's really understand
what is happening under the covers because it's so incredibly powerful. The
MESA cards can be modified since much of the FPGA information is published.
But unlike MACH3 where a simple checkbox changes the spindle step pin into a
pwm pin the FPGA world requires knowledge of the entire FPGA programming
environment and it can't just be changed with a check box on a set up dialog
box.
And in the LinuxCNC world one has to be very careful when asking a question in
fear of being chastised for not doing their own research and memorizing all the
command line options of a 1970's based serial non-graphical terminal interface.
So open source is truly open source but I'll bet 95% of the members on this
forum haven't a clue what Gene or Thomas means when they post how they are
rebuilding the kernel for a Raspberry Pi.
It's like saying that it's open source, all publically available written in an
obscure dialect of Tibetan Chinese available to only a handful of scholars
versed in that language. And if this dedicated controller is designed with
full schematics and software, like a Beaglebone for example, who supports the
hardware?
I guess what I'm saying is that other than what comes in a PC connected to an
electrical interface break out board, the rest are all really just dedicated
systems with the only interchangeable part being the PC. And given the
terrible latency on the PC I'm using for LinuxCNC even those aren't that
interchangeable.
But I do think there is a need for that $300 controller that does more than the
ones from China.
I hope this ramble makes some sense.
John Dammeyer
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