Although this is off topic by now, I agree with Charles. A CNC machine should be just that, and have a reliable stand alone PC at its core. A coffee machine makes coffee, and a CNC cuts metal. The thing I love about LinuxCNC is that when paired with Pico or Mesa hardware it provides an affordable alternative for machine builders. By remaining compatible with standard g-code a LinuxCNC control has capabilities close to that of a Fanuc or Haas. This, in itself, is amazing! All the other complaints about what it doesn't do, or what it's called for that matter, don't even bother me. Thanks to the developers of LinuxCNC, I can cut metal with the accuracy of a $40,000 machine on a $4000 machine. How can you not love that?
-----Original Message----- From: charles green [mailto:xxzzb...@yahoo.com] Sent: Tuesday, February 21, 2012 5:47 AM To: Enhanced Machine Controller (EMC) Subject: Re: [Emc-users] Latency - was Re: Which video card/driver for LinuxCNC? the allocation of computing resources seems to be a recurring theme with pc based machine controllers. while i have wished for an accesible pocket calculator gui more than one time while standing in front of a machining center console, i have almost never wanted to surf the web or send emails while doing so. the enhanced machine controller spans a disparity between its intended function and the common usage of it's supporting hardware. maybe there is a workaround? when i installed linux cnc packages, one of the steps was drive partitioning, in case there was another OS already there, with some kind of neutral zone for exchange of data when switching the pc from one dedication of control to a different dedication of control. why not do the same thing with an enhanced machine controller? in one mode, the pc has the sole function of machine control and user interface for machine control. in the other mode, the pc has the common functions like internet and anything else in an OS's routine employ. i only have a very basic understanding of pc construction, so there might be some sort of fatal flaw in the idea of a dedicated machine control operating mode for a pc. however, my suspicion is that such operation has not been pursued for reasons of convenience of having a do-it-all pc operation mode. this may not always be advantagious. for example, imagine waking up in the morning, turning on the coffee maker, showering, and then finding that the coffee pot is empty because the coffee machine had a problem downloading the most recent bean roast sensing algorithm. --- On Mon, 2/20/12, Jon Elson <el...@pico-systems.com> wrote: From: Jon Elson <el...@pico-systems.com> Subject: Re: [Emc-users] Latency - was Re: Which video card/driver for LinuxCNC? To: "Enhanced Machine Controller (EMC)" <emc-users@lists.sourceforge.net> Date: Monday, February 20, 2012, 9:54 AM Roland Jollivet wrote: > > My question is; if one built a headless system(no video) and disabled > drivers wherever possible, would such a system be fast enough to run DC > servo's and read the encoders on the parallel port? > You have to figure this out for each case. What is the maximum encoder RPM at the desired rapid feed rate? (Don't forget belt reduction.) What is the base thread rate? For example, 60 IPM, 1000 cycle/rev encoder and a 2:1 belt reduction to a 5 TPI ballscrew. So, that is 60 * 5 * 2 * 1000 * 4 (encoder quadrature) / 60 secs/min = 40,000 counts/second. Well, that is a bit iffy, a count every 25 us. And, remember that if the encoder exceeds the rate at which the computer can count the pulses, you get a servo runaway, which is a lot worse than just losing position with a stepper. Now, if 30 IPM is OK, and you have 250 cycle/rev encoders directly coupled to the 5TPI screws, it should work fine, but that is a lot of compromises to avoid a better interface. I generally think that running steppers via software step generation is not a great thing to do, and running servos via software encoder counting is far WORSE! So, now you are suggesting using TWO computers instead of using purpose-built hardware to interface to the motion system! Now, you have to have TWO hard drives to back up, and TWO computers to boot and shut down cleanly. There may be times such an arrangement is desirable, but I really think it is the wrong approach. Jon ------------------------------------------------------------------------------ Try before you buy = See our experts in action! The most comprehensive online learning library for Microsoft developers is just $99.99! Visual Studio, SharePoint, SQL - plus HTML5, CSS3, MVC3, Metro Style Apps, more. 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