Watch the video. The guy is using a normal laptop PC and LinuxCNC. Already we know the real time performance is not great. He is sending all the data to his milling machine over one Ethernet cable using the built-in Ethernet port. He mills a circle and the circle is dead-on perfect to his ability to measure with digital calipers.
We don't have to argue if this can be done or not. I've been thinking about how this can happen with horrible not real-time system. How does he keep the axis in sync? Look at the bits in the wire: The PC sends a single packet that has three 32 byte payloads for X, Y and Z. The bits are sent at one hundred million bits per second so the time between payloads is always EXACTLY 0.00000256 seconds. There is far less than a nanosecond of jitter in that number. The axis synchronization is better then most of us can measure and he did it with a laptop. Another way to look at it is that he does is not send the X, then the Y then the Z. He sends (X, Y, Z) points all at once in one ethernet frame then some time latter, more or less in real time comes the next (X,Y,Z) point. He is getting picosecond axis sync for "free" without need for a real time OS. The key is that all data for every axis is inside the same frame so the timing is controlled by the crystal oscillator on the Ethernet card, not by software inside Linux. We are likely looking at pico second level jitter. Then of course he is uses an $8,000 servo controller to hit those (x,y,z) points so no surprise the circle is spot-on perfect. I am always impressed when some one finds a way to do impossible things with no effort. On Sat, Oct 28, 2017 at 8:53 AM, Nicklas SB Karlsson < [email protected]> wrote: > > > Most LinuxCNC systems ar set up so the PC sends out things like PWM or > > > step/directin. These are VERY low level but with this setup, not the > > > communication is at a much higher level, even the home and limit > > > switches are detected by the controller. > > > > You would still need a low-latency link to do coordinated moves such > > as circular interpolation, though. > > Yes coordinates move is why good real time perfomance is required. > > I guess a pick and place machine would not require hard real time, tell > servo to travel to position and wait for it to arrive, this may also > increase perfomance because servo could be ran at maximum while for > coordinated move it's not possible to move faster than known beforehand. > > ------------------------------------------------------------ > ------------------ > Check out the vibrant tech community on one of the world's most > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-users mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-users > -- Chris Albertson Redondo Beach, California ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
