On Wednesday 29 November 2017 22:42:11 Chris Albertson wrote: > So the spindle spins about up to about 3,000 RPM. That is 50 rev. > per second. You have a 1,000 line encoder so that is 50,000 lines per > second on each channel. You should seeing a 50 KHz square wave on > both A and B channels. I don't understand the 1.8 MHz reference. > Theres some ringing on the edges that my fauncy digital scope may be counting. But your math is wrong, the way its hooked up its a 1000*7161.17=761,170 line/rev, * 3000=38,058,500 hz. I do believe thats a bit much for a 5i25 to process.
I set the sample clock up 3x, which made it take the tach to the redline at 3k, but obviously that needs explored to find the top frequency it can sample at. Or a lower count encoder generator. In digging out the 74ls86's to make a differential receiver, they were in a box of parts I had collected to make a jog pendent, not with encoder dials, but with teeny little steppers salvaged from very old floppy drives. Feeding those 6 wire motors into a 74ls86, rigged for a wee bit of hysteresis, and it should look close enough to a std encoder at the outputs of the 74ls86 to function rather well as a 200 line per motor rev encoder, which with this oddball hookup would divide that high gear figure by 5 making it=7161.17/5= a 1,432.234 lines per spindle rev encoder generator. That, *3000/60 should give a signal at 71,611.7hz, which the 5i25 can handle standing there looking bored. Its not quite that simple because the motor output if not limited, can destroy the ls86. Biggest problem is reworking the mount to fit these teeny little motor thingies. Probably by excising this one and using it for a template to bore the corner holes in a new one. All that done on the fattened up x1 out in the shed. The confusing part of the math above, and the use of the experimentally determined ratio between the a/b pulses, coming from the encoder ON the motor, and the index pulse which is coming from the old encoder ON the spindle. So we actually count the pulses between the index pulses and use that for the encoder_scale. The idea is that the encoder-position stays in synch with the index pulse being used. Clear as mud, but... It ought to work. Until it skips a beat at the bottom of a g33.1 operation while turning around. Thanks Chris. > On Wed, Nov 29, 2017 at 4:38 PM, Gene Heskett <[email protected]> wrote: > > Greetings all; > > > > Does anyone have a 256 line/rev encoder that would like a 1000 line > > version? > > > > Sitting on the rear of the motor, with the encoder filter in a 5i25 > > turned off, I can get to around 1750 spindle rpms before the 5i25 > > encoder falls over and the tach drops to zero. > > > > Looking at the signals, it may yet be in the SainSmart BOB as the > > encoder has a differential output, and I'm only useing 1 of the > > leads. When enabled, the motor settles at about 3x what the encoder > > can track, and looking at the bob with a scope, I see its something > > north of 1.8 MHz with an rc slew rate limited waveform, which the > > bob cleans up to a square wave but nowhere near a 50% duty cycle, > > 15% high time maybe. > > > > I have some comparators of the *86 variety that I can make > > differential receivers out of, which should even up the duty cycle > > to around 50%. But I'm not sure that will be enough since the motor, > > in high gear, can do 2950 at the spindle until a thermal in the > > windings stops it for about a minute. So I normally don't run it > > above 2750. > > > > So I'll make the differential to single ended gizmo to see if it > > might be enough. If thats not enough, maybe somebody wants a higher > > resolution encoder they can direct couple to their spindle? > > > > I just noted the encoder_sample is set for 500000 in the ini file. > > Would turning that up help, or is that the limit? > > > > Thanks all. > > > > 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 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
