My steppers are set for half stepping and are working well enough just not blazingly fast. I’m only pushing 36v to them at the moment. The drivers I have are limited to a max of 50v
My main issue is the spindle motor rpm fluctuation. I’m in the process of trying a different BOB that doesn’t appear to use isocouplers between it and the outputs. It does however use them for the inputs. I’ll post up what I find. I’m hoping for better results with this different brand of BOB. On Wed, May 6, 2020 at 11:19 AM John Dammeyer <jo...@autoartisans.com> wrote: > Hi Gene, > Thanks for the details. > However, I'm trying to learn how LinuxCNC works at the simple level. Not > with a high speed co-processor tied on the output doing the heavy lifting. > Then it becomes LinuxMESA rather than LinuxCNC and those appear to be very > different animals. > > Kind of like saying in third gear my electric bicycle makes funny noises > and doesn't go as fast as I think it should and having someone mention > their Honda 350 motorcycle has no problem with speed and doesn't make noise > in third gear. > > Now I don't own either an electric bicycle nor a Honda 350 so it's really > just an example. I do own a MESA 7i92H and expect to be able to tie onto a > hi res spindle encoder with it when I finally get the variable speed motor > mounted. > > But right now it's all about the electric bike. > <BIG GRIN> > > John > > > > -----Original Message----- > > From: Gene Heskett [mailto:ghesk...@shentel.net] > > Sent: May-06-20 6:35 AM > > To: emc-users@lists.sourceforge.net > > Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 encoder > > > > On Wednesday 06 May 2020 04:41:17 John Dammeyer wrote: > > > > > 1000 PPR encoder turning 300 RPS (18000 RPM) will produce 300,000 Hz > > > output. At 10000 RPM it's 167 RPS or 167Khz. > > > > > > I've been reading through the LinuxCNC source code for the last hour > > > or two. If one was just using a parallel port and not sophisticated > > > external hardware the hal_parport.c code looks like it reads the input > > > at the base_period rate; say 25kHz => 40 uS. > > > > > > If you figure a standard mill running max 3000 RPM (50 RPS) then a you > > > probably need to look at the spindle encoder at least twice per > > > encoder period. At 25kHz we're seeing a ParPort task run time of 40 > > > uS. So I'd guess the max pulse size from the spindle encoder has to > > > be at least 80 uS. > > > > > > The spindle at 50 RPS uses up 20mS. Divide that by the 80uS implies > > > the largest usable encoder is 250 lines. > > > > > > Have I got that right? I've not found the spindle support code yet. > > > Only the HAL install code. > > > > > > John > > > > Neither have I John. But I've made it a rule of thumb in my builds, that > > the instant I thought of a spindle encoder, my thoughts just assumed > > that it would be read by external hardware if for no other reason but to > > remove that 1 kilohertz servo sample rate with its propensity for > > missing the higher speed events, from the equation. I have given base > > thread rates down to 27 u-secs on the D-525-MW boards and simply did not > > get the desired results on either machine until I put a 5i25 Superport > > in the pci slot. With a 50 megacycle sample clock, it doesn't miss a > > lick. > > > > Low counts from the encoder finally got the best of me on the G0704 so > > although I was proud of the disk and photo-interrupter with 268 slots > > I'd made for it, I bought a 1000 line differential output omron encoder > > from fleabay for a $21 bill, made and installed an extension shaft to > > drive it on the rear of the motor and installed it there, but left the > > index signal from the spindle intact. Wrote some hal code to measure > > the counts, and put tally switches on the gearshift knob to tell hal > > which gear it was in. > > > > That 1000 line encoder had to have a pair of $2.00 rs485 transceivers > > wired as rx only to make a single ended ttl signal out of it that was > > actually rail to rail. Worked up to about 300 rpms and found the opto's > > in the sainsmart bob were way too slow, so I bypassed them, works great. > > Where before, the 268 count encoders quantization noise was banging on > > the motor hard enough it sounded like every bearing in the head was > > square and well on its way out, now it runs dead silent up until when > > rigid tapping with a 5/16 or bigger tap that works the motor too hard > > and I hear the iron in the motor squeak as the 17 amp current limit > > setting in the pwm-servo amplifier kicks in. > > > > That 704's head gears are plastic, and I've no clue why I haven't > > stripped them doing rigid tapping with it, but I haven't yet. That > > spindle, originally a 2250 rpm fwd, 1100 reverse, now with Jon's > > pwm-servo driver and a shop made psu good for 125 volts and a 20 amp > > surge, now turns 3000 revs in either direction. The effective encoder > > count/scale changes with the gear shift of coarse but that just more hal > > modules to fix. > > > > The scale in high gear is a bit over 7000 counts per spindle rev, and is > > a bit over 14,000 in low gear. So at 1500 revs in low gear, its about > > 14150 counts per rev, so (1500 * 14150)/60=353750 cps into that 5i25 > > cards A/B inputs, and hasn't missed a lick yet. My optical disk for an > > index came loose and ate the opticals up so there is now an ats667 > > reading a screw glued to the side of the drawbar cap for an index > > generator. > > > > Since the gears are plastic and not molded for easy gear shifting, I took > > advantage of the tally switches and swapped the mux2 that changes the > > scale for a mux4, and did a setp for about 15 revs at the motor to the > > unused inputs, so when between gears its turning slowly and the gear > > shift is without the drama of grabbing the spindle and manually > > re-engaging the gears by hand. And the control response is fast enough > > I can change gears while its running wide open. > > > > I have since run out of i/o on that machine, so that 5i25 is now driving > > a 7i76D on P3, but the machine runs the same. > > > > And I am still convinced the bare parport is a bad idea. But its a piece > > of cake for the 5i25. > > > > > > > -----Original Message----- > > > > From: andrew beck [mailto:andrewbeck0...@gmail.com] > > > > Sent: May-06-20 12:31 AM > > > > To: Enhanced Machine Controller (EMC) > > > > Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 encoder > > > > > > > > John while we are on this subject got a quick question. Just want > > > > to check my maths. > > > > > > > > My encoder card on vfd max count rate is 300Khz. Max rpm is > > > > 10000rpm > > > > > > > > So a 1000 ppr encoder should give me 18000 rpm at 300khz. I just > > > > need 10000 rpm so that should be well within spec > > > > > > > > Regards > > > > > > > > Andrew > > > > > > > > On Wed, May 6, 2020, 6:45 PM John Dammeyer <jo...@autoartisans.com> > > wrote: > > > > > > -----Original Message----- > > > > > > From: Nicklas Karlsson [mailto:nicklas.karlsso...@gmail.com] > > > > > > Sent: May-05-20 9:13 PM > > > > > > To: Enhanced Machine Controller (EMC) > > > > > > Subject: Re: [Emc-users] Fluctuating RPM using CUI ATM 10 > > > > > > encoder > > > > > > > > > > > > > Do you have a dual trace 'scope? Spin the spindle and look at > > > > > > > the > > > > > > > > > > input > > > > > > > > > > > > and output of the opto-isolator. See if there really is a > > > > > > > lag. If > > > > > > > > > > you > > > > > > > > > > > > have a new scope would you have it capture the screen and post > > > > > > > it. > > > > > > > > > > I'm > > > > > > > > > > > > really skeptical that those isolators are THAT bad. > > > > > > > > > > > > > > Here is the datasheet for the opto. > > > > > > > https://www.mouser.com/datasheet/2/143/EL817-G-26528.pdf > > > > > > > They claim an 18 uS rise and fall time. A 1KHz square wave > > > > > > > will > > > > > > > > > > have a > > > > > > > > > > > > 1000 uS period and a 500 uS pulse width at 2 KHz the pulse > > > > > > > width is > > > > > > > > > > still > > > > > > > > > > > > more than 10X the raise time of the opto. But maybe the > > > > > > > opto is a > > > > > > > > > > fake > > > > > > > > > > > > counterfeit part with very poor performance. > > > > > > > > > > > > Opto couplers are rather slow. With a high resolution encoder > > > > > > frequency > > > > > > > > > > could be maybe up to a few hundred kHz, > > > > > > > > > > > 2000*period/revolution*3600rpm=120000period/second=120kHz, > > > > > > 200PPR will > > > > > > > > > > be 12kHz at 3600rpm, 1/(2*18?s) = about 27778Hz = > > > > > > > > > > > about a little bit below 28kHz if mad no misstake. > > > > > > > > > > I think your math is out. Most of the hi res encoders are running > > > > > 2500 lines per rev. Many are less. But we're only looking at > > > > > one encoder channel and that works out to twice the number of > > > > > edges but the actual frequency is still lines per rev per second. > > > > > > > > > > So how many revs per second is that? You have to divide RPM by > > > > > 60 to get revs per second so 3600 RPM is 60 RPS. > > > > > > > > > > Now you have 60 * 2500 Hz = 150kHz. Still way too high for that > > > > > opto-isolator. > > > > > > > > > > Now if you do like Sam did for his hex milling you update the > > > > > encoder. But initially he was milling with about 60 teeth and > > > > > Linux is more than fine for that when power tapping etc. So 60 * > > > > > 60 is 3600 Hz and the opto would be fine for that. Even 200 > > > > > lines at 60 rps (3600 RPM) is 12,000 hz. > > > > > > > > > > Don't understand how you got 27778Hz > > > > > > > > > > John > > > > > > > > > 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) > > If we desire respect for the law, we must first make the law respectable. > > - Louis D. Brandeis > > Genes Web page <http://geneslinuxbox.net:6309/gene> > > > > > > _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
