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
