On Monday 06 November 2017 08:31:58 Todd Zuercher wrote: > ----- Original Message ----- > > > From: "Gene Heskett" <[email protected]> > > To: [email protected] > > Sent: Sunday, November 5, 2017 10:16:14 PM > > Subject: Re: [Emc-users] excedrin headache #487.69 > > > > On Sunday 05 November 2017 21:21:09 Peter C. Wallace wrote: > > > The Hostmot2 velocity estimate system measures velocity by > > > counting the number of quadrature edges divided by the time > > > between the first > > > and last edge so more edges helps (by making quadrature error less > > > important), but in any case is much better than just counts/servo > > > thread > > > > And my pid.feedback is this velocity signal but averaged over the > > last 4 > > incoming edges. That helps a lot at lower speeds. > > > > Thanks Peter. > > > > Cheers, Gene Heskett > > -- > > Actually no, it wouldn't be. (at least I don't see how it could be.) > When using Mesa hardware Linuxcnc does not see any of the encoder > edges. It only sees the position and velocity values calculated by > hostmot2 and sent every servo thread cycle. What you are probably > doing is averaging the velocity value returned by hm2 for the last 4 > servo thread cycles. > I think you are probably correct. But by averaging the last 4 "edges' in a fifo, clocking of fifo determined by getting a different value than the last reading on the previous thread cycle, which works by addf'ing the mux2's that serve as the sample holds in reverse order, it shifts the data 1 mux2 at a time, but does it all in the same servo cycle. The outputs of each mux2 are then sum2'd into a pair of sum2's with their gains set at .25, and they feed a final sum2 to get the average of the last 4 velocity changes reported by the encoder. At slow spindle speeds it reads the same velocity for several servo cycles and that means the fifo doesn't get clocked until a different velocity does come in. The reduced "noise" in the resultant velocity signal average then allows a lot more Pgain to be used without hammering the backlash in the head gears, and gave me an extremely stiff spindle speed control.
As demoed to me Saturday, the F0 and Igain combo gave horrible performance, stalling the spindle because it wasn't fast enough to see the spindle slowing as the cutting load came on. I was forced to stop the peck cycle, loosen the draw bolt, set the tap back into the partial thread it had cut, and using a 22mm wrench on the flats of the TTS holder, drive the tap by the wrench while guiding it with the loosened r8. This of course took around 100 lb/ft on the ER32 nut to keep the 7mm ER collate holding the shank of the tap from slipping. What I need for such monkey business is a precision version of the old fashioned carpenters brace chuck, at about 2/3rds scale to grab the square butt of the tap to drive it. But no one makes it, so at some point I'll have to make my own. This would also tend to make the tap more self-aligning with the hole, an advantage when using the crooked taps I can get quickly at Lowes or Home Depot. Every tap I have seems to have warped in the heat treatment, and will cut an oversized thread when its constrained by the precision grip of a collet. Noticeably snugger threads are cut when the r8 is loosened allowing a small wobble, maybe 5 thou, to the butt end of the TTS holder. I should realize that with the gearing choices in the G0704's head, its never going to drive a tap in steel bigger that a 4mm, asking it to deliver the torque to drive a 10mm in cast iron is asinine. But hope springs eternally. :) With a 10x bigger motor, or 10x slower gearing, neither of which is ever going to happen on my remaining watch, maybe. But the Chinese designers of the G0704 never dreamed someone would equip it for rigid tapping. As has been said often, I got exactly what I paid for. Thanks Todd Z. 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-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
