Sebastian Kuzminsky wrote: > John Kasunich <[EMAIL PROTECTED]> wrote: >> >>The problem is going to be getting usable velocity feedback. Your >>encoder sampling is at 25uS, and your PID is running at 75uS. That >>means in any one PID period, you get either 0, 1, 2, or 3 encoder >>counts. Not much resolution. > Very good point! That's why DC tach generators were all the rage 30 years ago. > > That makes sense. If the load doesnt slow the motor down enough, it > looks like I'll need to buy a Pluto-P or a MesaNet product. > > Bummer, I was hoping to do it all in software on the PC using just the > parallel port for I/O. > >
There are things a big, heavy, general computing CPU just can't do well, and incredibly fast interrupt service is one of them. Sampling an encoder in software is a bad way to do it, because of all the time you are missing transitions between the samples. For instance, my servo control boards all sample the encoder at 1 MHz, and some people complain that isn't fast enough for them! Also, trying to do PDM or PWM in software, on the same general-purpose CPU runs into the same difficulty. My PWM board runs with a 10 MHz clock, mostly for compatibility with the step generator board. The next version will probably run at 40 MHz, to give finer time resolution. Jon ------------------------------------------------------------------------- This SF.net email is sponsored by: Splunk Inc. Still grepping through log files to find problems? Stop. Now Search log events and configuration files using AJAX and a browser. Download your FREE copy of Splunk now >> http://get.splunk.com/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
