On Monday 10 June 2013 14:07:11 Gene Heskett did opine: > On Monday 10 June 2013 10:05:54 dave did opine: > > On Sun, 2013-06-09 at 22:05 -0400, Kent A. Reed wrote: > > > On 6/9/2013 9:08 PM, Jon Elson wrote: > > > > Gene Heskett wrote: > > > >> Looking at its voltage output, with the motor disabled so there > > > >> is no feedback,off = 0.125 volts > > > >> click fwd button= 0.382 diff = 0.257 > > > >> click + button = 0.942 diff = 0.560 > > > >> click + again = 1.584 diff = 0.642 > > > >> click + again = 2.302 diff = 0.718 > > > >> click + again = 3.094 diff = 0.792 > > > >> click + again = 3.970 diff = 0.876 > > > >> click + again = 4.940 diff = 0.970 > > > >> click + again = 6.04 diff = 1.100 > > > >> click + again = 7.33 diff = 1.29 > > > >> click + again = 8.88 diff = 1.55 > > > >> click + again = 9.90 diff = 1.02 > > > > > > > > URK! It isn't even monotonic! That is harder to fix with a > > > > piecewise-linear > > > > interpolation. (Some simplistic codes won't handle that.) > > > > > > Ummm, I expect you mean the differences aren't monotonic, Jon. > > > > > > Actually, plotting Gene's data as a set of twelve points X, V where > > > X is the number of clicks, I get a pretty decent graph --- looks > > > like a parabolic curve opening upward, with a bit of a burble in > > > the next to last point (or last two depending on how you look at > > > data). > > > > > > Trying a second-order curve fit (using the free tool simfit, but > > > there's lots of other tools) got me a decent looking result with a > > > plot of residuals that also gives the impression that the last two > > > points are questionable compared to the rest. > > > > > > I don't chose simply to post the results because I don't believe any > > > single experimental run is sufficient. Repeat this experiment three > > > or more times, Gene, so we can begin to get an idea of the quality > > > of the data and then we can talk. > > > > > > Regards, > > > Kent > > > > Except for the last point that looks like it should fit as a 2nd order > > polynomial. Since we can to a considerable amount of calculation > > between servo cycles calculating a simple polynomial should be simple > > and fast. > > > > Dave > > The last data point is smunched because thats all the C41 can output > after I had changed a 2.7k resistor out for a 12k resistor in an effort > to get the no pulses voltage low enough to reset the zero speed at > power on safety of the controller I'm using. I expect I can paste > another 12k across that one and still satisfy that logic since with the > 2.7k I had there originally, the off voltage was only .257 volts. With > the 12k, its .125 volts when off. But this is a separate thread and I > should have changed the subject line when I started discussing a PFM > control method. My bad,middle of the night musings & what ifs. :) > > Cheers, Gene
I just had another epiphany on this. Why change away from PWMGEN in the first place? Put it all in the interface on the other end of the cable, like this: In the interface, use the PWM true period to trigger an oscillator running a square wave at about a megahertz. I believe the PWMGEN itself is probably fairly linear in terms of its duty cycle vs commanded digital word. By using the pulse counter in the LM2907, and the same one shots to control the S/H driving the output, we should then get an output voltage whose transfer function is a lot closer to a straight line than I now have, with an update rate at SERVO_THREAD. And its all on the interface, with no architecture changes to LCNC at all. I got eagle running. Now, does anyone recall how big a board I can do in the free version? I ought to be able to stack this on top of the C41 itself, in the same foot print IOW. Now what do you all think? 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! My views <http://www.armchairpatriot.com/What%20Has%20America%20Become.shtml> [He] took me into his library and showed me his books, of which he had a complete set. -- Ring Lardner A pen in the hand of this president is far more dangerous than 200 million guns in the hands of law-abiding citizens. ------------------------------------------------------------------------------ This SF.net email is sponsored by Windows: Build for Windows Store. http://p.sf.net/sfu/windows-dev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
