> -----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 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
