On Tuesday 24 January 2017 02:10:53 Danny Miller wrote: > What drive and system voltage are you using here?
An M542T for x drive, and a DM860 for Z drive, with an 8 wire 230 oz motor for x, 20 tooth pulley to 40 tooth on the x drive, which is a probably too small ball screw. Z drive is a nema 34, 1600 oz, 30 teeth on the motor, 40 one the end of a 1450mm x 25mm ball screw, moves the carriage at nearly 80 ipm. 46 volts powers the M542T, and about 68 volts powers the DM860. > Toroids don't make any sense anymore. Switching power supplies DO > perform great, unless you overload 'em with BEMF, but a toroid is > vulnerable to that too. Specifically Meanwell switching supplies > perform reliably. I have a stack of 4 of them currently sitting on my chopsaw The spi bus is extremely susceptable to noise pickup. The switching noises from the supplies I bought could not be tolerated. I didn't use the little pcb from OHSPARK because its only traces were the ones for the source termed connections. No ground continuity at all in the .brd images I downloaded and printed letter sized images of that I used to count pin numbers when I made this spi cable.. So I cut a 40 pin drive cable off the end of an old ide drive cable, leaveing about 3/4", terminated that into about an inch wide pcd cut from a rat shack project board, putting the term R's needed, 3 of them, on this board and connected all the ground pins of the 40 pin side to the grounds on the 26 pin side going to the 7i90, and because of all the other cables that connect to the pi, this plugs into the pi, and this little pcb comes across the top of it, and runs down across the top of the pi to 7i90 until its folded at a 45 degree angle and points at the 26 pin plug about an inch away, a 26 pin plug then folds the cable down about 3/8" and plugs into the 7i90. Because this spi bus is fast, running at 32 mhz, and the switching noises ring like the liberty bell with harmonics in the 100 mhz range, theres nothing even remotely close to a real ground even if everything is grounded at a single bolt in the bottom of the box this is all in. With my scope on an isolating plug adapter and grounded to this bolt, the switching noises 6" away on a flat braided ground bus exceed 5 v p-p. I've about half a pound of ferrite chokes at the drivers power and output cables. I can clip onto the edge of a usb port on the pi's board, and 3" of air away, theres nearly 2 volts of this noise on most any ground pin on the 7i90. I have the error voltage range set for a bit over 1 volt in the ini file, but even 10 volts doesn't fix it, I get joint errors when they aren't moving in 30 seconds, and if I move a motor at 10% of its speed capability, the motors run, but are randomly "skipping a beat" and you can see the drive belt stop for a few milliseconds. I've had the motors take off and run 3" from these noise induced bus errors on several occasions while I was standing there contemplating my sins of years past. The on-screen dro often does not show these movements. Or the dro may show a 3 foot movement, which of course is when it throws joint errors in both joints. I have samples of an isolator chip ti makes requested, which are supposed to be able to handle digital data at 100 to 150 mhz, but they've not materialized in my mailbox yet. One of them would be ideal, a 4 bit model, with 3 sending data to the 7i90, and one bit going back the the pi, just what doctor Gene ordered. That "might" solve the problem. So at the end of the day I have two problems. Errors in the spi bus out the yang, and those errors then cause errors in the step timing that will stall the motor at 1/2 the speed its capable of. All caused by the noise from the drivers switching activity even when the drivers are powered by analog supplies. The cables to the motors are foil shielded, and that shielding is grounded to the common bolt as the cable goes by it on its way to the motor. Ditto the cable from the encoder, which is not grounded to the lathe except going by that star ground bolt. > Resonance seems to be resolved AFAIK like 10 yrs ago with GeckoDrive, > then GeckoDrive rendered obsolete by this DSP stuff, then THAT was > rendered obsolete by DSP+3phase. Of course this doesn't mean a > stepper can do 10K RPM, but the torque does perform to the spec > profile at least. > > Mechanical dampeners are obsolete, unless you want a retro "steampunk" > aesthetic. At this point I could care less what it looks like as long as it works. This is a run what I had on the shelf unless it won't do the job. Those were the last 2 motors I had. This motor, a Nema 24, is one of two slightly different birds I ordered 2 weeks ago. All the torque I could get, fitting in the space I had. > There's one exception that DSP drives can't tolerate a 4th order > system, i.e. a springy connection between the motor and load. Unless > the motor has its own dampening. But no one does a springy thing > like that. Ordinary spring couplers don't count as springy for this > purpose. The torsional give in the typical spring coupler can and sure will count heavily in the torsional vibration scene, I have seen a 230 ounce motor wind them up several degrees when the screw has reached the mechanical limit. They DO count. > > Yep full disclosure I drank one too many at the moment, but I'm > instinctively compelled to get right to the point and help you with > your resonance thing. Get some 3ph and the 3DM683 and I think you'll > start to cry. > > Danny > > > Its amazing the papers one can come across from a google search. > > For instance, this one bears testing out: > > > > <http://machinedesign.com/news/how-take-vibration-out-stepmotors> > > > > Look at the last wiring diagram. I may try this tomorrow with the > > small motor just for S&G. The theory is that it rotates the resting > > position by 1/2 of whatever the microstep angle is, with the real > > effect coming from there never being a condition where one winding > > is completely off. > > > > This should result in a smoother step whose absolute movement angle > > is more consistent from step to step regardless of the current > > setting, where with the upper two configurations, smoothness and > > equal angle per step performance is much more dependent on the > > current mapping in the driver matching the magnetic characteristics > > of the motor. I am going to put the nema 24 motor in but that > > depends on whether I had the great good sense to buy two of those 20 > > tooth pulleys, so I can bore the 2nd one to 8mm. It will be a bit > > under driven, the m542T driver does 4.2 amps peak at full song, but > > this motor says 4.5 amp rms for max twist. > > > > Might have to buy a heavier driver & toroid power tranny to feed it. > > This one is heating some feeding the M542T 46 volts at its full > > current of 4.2 amps peak. > > > > News tomorrow night maybe. > > > > > > Thanks Danny. > > > > Cheers, Gene Heskett > > ---------------------------------------------------------------------- >-------- 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
