> From: Chris Albertson [mailto:albertson.ch...@gmail.com] > To: Enhanced Machine Controller (EMC) > Gene, > > I did a search on the part number to gave and, they look really good but > cost $400 per axis vs about $60 for what I have. Yes, they are much > better. Did you find a better deal? > > Question for the group: > Assuming that you need about 3NM holding torque, what will $400 get you if > you want to use a servo motor? I'm thinking that these 3-phase closed > loop steppers are more comparable in performance and price to servos than > to cheap steppers. Anyone have a link to a source of small-size Chinese > servos and matching drivers. >
<RAVE_MODE := ON> Yes. I've been raving about the Bergerda series of AC Servos for a year now. I have a 1.8kW running the mill spindle and a 750W (2.39NM) running the knee (19mm shaft size) which cost just under $300. http://en.bergerda.com/ I also cast a mount and tried one of the 400W (1.25NM) units on the X axis and it was flawless too. But at the moment my cabinet won't fit the drives compared to the DC Servo HP_UHU drives and I didn't want to swerve in another direction until the mill was completely converted. When I change to ball screws I'll also replace the two DC Brushed motors which are huge in comparative size to the AC servos. They come in various flavours and sizes (ie frame/rpm/torque/shaft size) and all run on 220VAC. Pricing out from https://www.automationtechnologiesinc.com/products-page/ac-servo-motors the same DC brushed servo setup that I have comes out way more expensive than the AC servos when you add the driver and encoder and cable and DC power supply with one caveat. https://www.automationtechnologiesinc.com/products-page/dc-servo-motor/nema34-1125ozin-dual-shaft-servo-motor Shipping. Bergerda is not a aliexpress reseller but the actual manufacturer so payments go through Alibaba and they won't do slow mail deliver. Must be FedEx tracked therefore one motor can be very expensive. A big enough order could be done surface for considerable savings. I've been trying to connect them up with a North American supplier but so far no luck. Anyway, I bought extra 400W units for the eventual conversion to ball screws and one to replace the stepper on the lathe. The drives all run on 220VAC which can be an issue if you only have 110VAC available. Now why servos instead of close loop steppers? First the steppers still can stall at higher RPM so like standard steppers they are oriented to direct drive and slower rpm which means no torque multiplication with reduction belt drive. That generally means using a larger motor but they are definitely stable. I used a CANopen commercial unit a while back that was impressive although eventually we upgraded to a German J1939 controlled AC Servo. The biggest downside other than rpm is they are still stepper motors and noisy whereas the AC Servos are quiet. Dead quiet. And support has been excellent with one of their engineers even making an iPhone video of the button press sequences of the display to set up some parameters when I was having trouble. Oh one other thing that I did verify. Most of the cheap Aliexpress AC servos out there use cheap encoders. Bergerda made a point of mentioning the use high end Japanese encoders. So I took the cover off the end of the motor and grabbed the part number and name. Yes indeed. Japanese manufacturer and in singles through Alibaba came in at 3x the price of the cheap Aliexpress encoders. So with cheap you get what you pay for I guess. <RAVE_MODE := OFF> John Dammeyer > Next idea... > I looked up Gene's part and the motor/controler is sold as a set. I can > see why. But I see I can buy a 3-phase stepper motor for about $100. So > we pay quite a lot for the driver and encoder. I can buy a 1000 line > encoder for under $20 and close the loop with a $4 microcontroller and > three h-bridges. I've done this many times using DC brushed gear motors. > (My use case is robotics but it's identical to a multi-axis mill.) > > On Sat, May 1, 2021 at 6:30 AM Gene Heskett <ghesk...@shentel.net> wrote: > > > On Saturday 01 May 2021 08:35:12 Thaddeus Waldner wrote: > > > > > So these are actual stepper motors and not 3-phase BLDC motors with > > > step/direction input? > > > > yes, and while I said a step loss will stop them it has to exist for an > > unspecified time frame. You can fasten them down, put a vice grip on the > > shaft and turn them 1/4 turn before they error, they will resist > > mightily and if you let go of the vice grips quick enough, they'll catch > > up to a zero error and just keep on trucking. I can, creeping along with > > my jog dials, run a carbide tipped tool into a stationary chuck jaw, and > > when its found itself jammed, it shuts down the output drivers and > > bounces about 10 thou clear of the chuck, all without damageing the chip > > in the tool. The machine will obviously need re-homed as I have the > > volatile option set in the .ini file. Thats a 25mm z screw, but my x > > screw is only an 8mm, so while its wired I've deferred to the size of > > the screw and the possibility of damaging it, and not tested it > > similarly with its shorter, 2NM rated motor. That screw today seems to > > be made of pure unobtainium, its half of one of a triplet I bought from > > Stuart St. about 15 or more years ago to cnc the smallest hf mill. > > > > > I always assumed that it�s the latter, with the difference being lost > > > in translation. > > > > So did I, but installing one, replacing a stepper that ran burn you hand > > hot, and finding it stone cold after half an hour powered up but the > > only move was homing the axis was quite the eye opener, the motors > > holding current is determined by the encoder error. No error=not enough > > holding currant to make feelable heat. You think its shut down, until > > you try to turn it... > > > > [...] > > > > 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 > > > > > -- > > Chris Albertson > Redondo Beach, California > > _______________________________________________ > 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
