On Tuesday 07 November 2017 23:07:36 Jon Elson wrote: > On 11/07/2017 08:58 PM, Gene Heskett wrote: > Hmmm, your raw encoder signals seem to have a LOT of width > variation. Since your time scale is 20 ms, there are 20 > samples between screen divisions, so the sampling rate is > not likely to be the cause. Generating encoder velocity > from timing the edges suffers if there is poor accuracy of > the state transitions, and would be expected to produce a > jumpy velocity just like what you showed in a previous > Halscope trace. A very poor eyeball guess at the A-B trace > looks like you might get 10 - 20% velocity error easily with > those duty cycle variations. This ought to show up on an > actual scope, to verify it isn't in the Mesa -> HAL part of > the system. > > Jon > They are visible on my 100 mhz hitachi dual trace, but not to the extent shown by the pix I just sent, Jon. Quantization errors keep adding up.
I'm looking at the Omron 2500 line encoder for a touch over $40, and at least a month to get across the big pond. But while it looks to have ball bearings, they are probably vxd's. Shitly stuff thats not really fit for roller skate wheels. No clue how hard it might be to put decent bearings in it. I'd like to see if I could put it on the rear of the motor, but it has no back shaft so I'd have to take out the cover and make that, probably epoxying it to the end of the shaft. Or, using the center thats in it, bore and tap it for a 3mm bolt, which wouldn't come loose if the motor bearing got hot. I'd ignore its z output and continue to use the existing index, changing the encoders scale to match the gear change. But even well aligned, I am concerned with how long it would live at those rpms. Can you pretend to advise? As in is the idea worth pursuing? Or should I make another of those disks, but first get my A axis moving, which should remove any variations in slot timing by elimination the xy backlash's incomplete compensations. But I'd still be stuck with a low slot count unless I can locate some mills with only 0.010 tip diameters. IIRC I used several mills out of a ten pack of .028" diameter mills to make that one, and don't have any more of those left. That also begs the question about how small a slot is practical with these honeywell interrupters too. I should tour yard sales looking for dead $5 printers I suppose... They have very fine pitched wheels and matching encoders in /some/ of them. Thanks Jon. > ---------------------------------------------------------------------- >-------- 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 > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
