On Wed, Sep 15, 2010 at 10:21:03PM -0500, Jon Elson wrote: > Now, if you use the OUTPUT_SCALE of 0.889, and PID is limited to +/- 1.0 > as the > maximum range, it will limit the DAC output to +/-1.12 V. Is this > reasoning right?
Yes I think so. That's why Stuart S has his pid maxoutput set to 8, which is the same as the machine's maxvel. That lets pid units be real world units inches/sec. It turns out he could have used scales of 1 all the way through and set his amp gains so 1 volt = 1 inch/sec and his numbers would have been really simple. But in general that's not going to work well unless you happen to have an 8 or 9 inch/sec machine. Mine is about that speed too, and I *did* adjust the amps so the dacs are 1v = 1ips. I have an OUTPUT_SCALE of 10 (because of the mesa full scale being +-1 instead of +-10 at the hal pin). I have pid maxoutput of 10. My tunings are P=300 D=2 FF1=1 and the fine adjustment of tach gain and dac offset were just done with the amp knobs. I have excellent response and following with acceleration at 35. > The limit of the PID output is set by parameter pid.n.maxoutput which is > set (in my > sample files) by ini parameter PID_MAXVEL, not a really accurate > description. > I have it set to 12.0, which also looks wrong! Yeah I wondered in his case whether it should be set to some number slightly higher than the machine maxvel for some headroom. Or maybe to whatever number allows up to 10 at the dac. Maybe a separate setting is better for that reason. It's tempting to leave it unset (unlimited) to give people one less number to worry about, but you can get integrator windup forever then. > Ah, but so you need to set the pid.n.maxoutput to 10.0 if you want to > get 10 V out of the > DAC, or you can set pid.n.maxoutput to 1.0 and then set OUTPUT_SCALE to 0.1 > Hmmm, neither of these is totally self-explanatory, is it? > Documenting some of this crap would help, though. I am painfully aware > that compared > to some of the other documentation on hal drivers, the PPMC is AWFULLY > terse. It would be nice to have good documentation for how a velocity mode setup should work. I have gone through it with several people - I don't think it's written anywhere. People think they are overly complicated, but dang they give unbeatable results once they're set up. If you start with a tuned working velocity loop like Stuart S has on his running machine, you can't go wrong. > You must know this as you are using "the source IS the documentation". Yep, you're not kidding. Chris ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
