On Sunday 09 December 2012 21:53:04 andy pugh did opine: > On 10 December 2012 01:26, Gene Heskett <[email protected]> wrote: > >> Not in your case, as encoder velocity is the controlled quantity, not > >> the derivative thereof. > >> > >> encoder.velocity is only an appropriate feedback-deriv term in a > >> position loop. > > > > But this is not a position loop per sei, its a velocity loop, working > > in the rps domain. Does that not change things, and if not, why? > > Yes, it changes things a lot. It means that you should _not_ connect > the encoder velocity to the feedback-deriv pin, as in this case the > encoder velocity is most definitely not the derivative of the > controlled quantity.
It is supposed to be a linear representation of the instant rps. Unforch the halscope is too fast to verify the speed linearity at sub 1 rps speeds. I did set the -deriv level down from its default 1.0, to .25, but could not see any effect at what I guessed was roughly .5 rps. At creep speeds the error hovers around -0.5, and generally stays there up to about 5 rps, at which point its like a load drops off the motor as the error changes polarity to about a +_0.6 or .7 all in about .1 rps and stays there till about 9 rps, then goes back negative all the way to 21 rps. So that is another effect I hope to stumble over. > Now, if you had a pin which (by some magic) measured spindle > acceleration, then that would be the thing to connect to the > feedback-deriv pin. > However, no such pin exists short of fitting an accelerometer to the > spindle, and nothing you can do in HAL is likely to do a better job > than the internal differentiator in PID. Ok, that's plenty clear enough, so I'll disconnect that 'wire'. Thanks Andy. Cheers, Gene -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) My web page: <http://coyoteden.dyndns-free.com:85/gene> is up! Dealing with failure is easy: Work hard to improve. Success is also easy to handle: You've solved the wrong problem. Work hard to improve. I was taught to respect my elders, but its getting harder and harder to find any... ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
