On Wednesday 30 May 2018 11:05:28 Kurt Jacobson wrote: > Gene, that makes sense about the software ADCs possibly being too slow > to keep up with the rapidly changing input. > > I have pot overrides on my machine and they work great. > I start all untested programs with feed and rapid ORs set to 0% and > then creep up rapid. When the gets to the first feed move it stops and > then I creep up feed all looks well. I really reduced my stress > testing programs this way, as the 300ipm rapids on my machine scare > the heck out of me even on programs I know are good! > > I have the 7i76 set to software mode 1 so I can read inputs 0-3 as > analog, and have pots connected to those pins.
Ahh, a 7i76, which I've no experience with. > The ADCs in the 7i76 are only 8bit, but I guess I don't know if they > are software or hardware. Either way the seem to be plenty fast > enough. I do get some dithering of the OR value read from the pots, I > have a custom HAL comp that adds some hysteresis to settle this down. Makes sense, as an 8 bit is pretty coarse so will have some natural dither. > I agree with you that if and number of IO allows encoders would be > preferred over pots. > They can be had for a lot less then $20 each, more like $2.50: > https://www.ebay.com/itm/232735252724 True, but the mpja encoder seems to have a better "feel", and looks precision to boot. I thought it may have a short life, but in several miles of jogging that Sheldon, the only thing I'd change is the separate pushbutton that enables it to change its own range on a 2-5-10-20-50 scheme. At anything above 10 it can actually be spun faster than the sheldon can move so it runs until its caught up, but if it looks like too far, the dial can be backed up to stop and back it up. I got those pushbuttons from Lowes since I'm out in the puckerbrush here in WV, and have since found some buttons that don't need a 20 lb push, these 'click' but take another 5lbs to actually make contact, and thats confusing to the muscle memory. And it also means it takes both hands, unhandy when the button is immediately adjacent to the dial and with a softer button could easily be a one handed operation. But its the shoemakers kids story, the softer buttons are still in bags in the drawers under the lathe. I'd have to dis the x drive, and take out 8 1/4" bolts holding the new apron panel to the front of the carriage to get access with a hot soldering iron. > The nice thing is they also have a push button, which could be hooked > up to set the override to 100% just by taping the knob! For that purpose, handier than the turn button on the outhouse door! I wish these mpja dials had such a feature, I could do away with the #$ button. > For feed, speed and rapid ORs I use the halui pins set to take a > direct value count input. > Here is my HAL file that handles the ORs: > https://github.com/KurtJacobson/RF45-config/blob/master/overrides.hal Neat. But those are halui pins that need creating, I assume in the ini file? See page 453 in the docs for specifics. You've dug deeper than I in that dept. And I could learn from those few pages. In the case of the 7i90, I had encoder receivers to spare, so they got abused. :) But I actually wound up useing the a/b inputs directly IIRC. And don't recall ATM exactly what changed my mind. Oldtimers memory again... > When using the halui pins the sliders in most all the UIs update to > match the pot setting, with is very nice. > If I try and change the ORs setting with the slider nothing happens, > as the slider can't change the position of the pot so easily :D > Another advantage of the encoders instead of pots is you could adjust > the ORs with the sliders, and the encoder counts would be reset. > > Cheers Gene! > Kurt > > On Wed, May 30, 2018 at 9:43 AM, Gene Heskett <[email protected]> wrote: > > On Tuesday 29 May 2018 09:36:14 andy pugh wrote: > > > https://forum.linuxcnc.org/gmoccapy/34610-potentiometer-bug#111106 > > > > Most software A/D's need a stable input for the duration of the > > conversion, and successive approximation types are extremely > > sensitive to noise. Because either is slower than mollasses, taking > > many servo cycles to finally clock out their result, I'd never use > > them with linuxcnc. Too slow. > > > > What I would use rather than a pot, is one of mpja.com's 20$ > > encoders, and feed the quad signals to a counter as I have done for > > the jog wheels on the Sheldon. The counters can be limited both > > ways, so a rapid spin CCW can reduce the counter to a zero state > > quite rapidly. > > > > I am doing this on the pi, and because its rather complex in the hal > > dept, its all in a 200hz thread, and have effectively a real time > > control of how much "gain" per click, but on more speedy stuff it > > could be done in the servo-thread. Zero reason this same code > > string, with some changes in the setp's to control the output range, > > couldn't be used for control of feed speed in effectively real time. > > This would fail for very slow speeds of course, depending on how low > > you have the vfd programmed. I have mine set to shut down below 10HZ > > and the low speed boost set to limit at the motors nameplate FLA. > > Seems to work quite well despite the nearly full loss of any cooling > > fan, and its never got hot enough to consider an aux fan for > > cooling. > > > > However, for feed rate control, I do not see a handy input pin. Yet > > the axis slider works. ??????? Needs more docs. Or a better > > description of how the pots arm is connected to linuxcnc. The forum > > post doesn't say. > > > > Cheers, Gene Heskett > > -- > > "There are four boxes to be used in defense of liberty: > > soap, ballot, jury, and ammo. Please use in that order." > > -Ed Howdershelt (Author) > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > ------------------------------------------------------------ > > ------------------ > > Check out the vibrant tech community on one of the world's most > > engaging tech sites, Slashdot.org! http://sdm.link/slashdot > > _______________________________________________ > > Emc-developers mailing list > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-developers > > ---------------------------------------------------------------------- >-------- Check out the vibrant tech community on one of the world's > most engaging tech sites, Slashdot.org! http://sdm.link/slashdot > _______________________________________________ > Emc-developers mailing list > [email protected] > https://lists.sourceforge.net/lists/listinfo/emc-developers -- Cheers, Gene Heskett -- "There are four boxes to be used in defense of liberty: soap, ballot, jury, and ammo. Please use in that order." -Ed Howdershelt (Author) Genes Web page <http://geneslinuxbox.net:6309/gene> ------------------------------------------------------------------------------ Check out the vibrant tech community on one of the world's most engaging tech sites, Slashdot.org! http://sdm.link/slashdot _______________________________________________ Emc-developers mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-developers
