John. I love the Chinese servos too. And totally agree going direct to manafacture is much better.
I buy my servos with absolute encoders now. 1300000 ppr I think. Or might be 130000. Just a basic 750w servo 220v servo drive plus motor costs me about $220 usd last I checked. (this is with just standard 2500ppr encoders) I normally buy bigger ones like 3kw Absolute encoders are a extra 50usd And service is amazing. Case in point I was setting up some kollmorgen servo star drives last week. Support was nothing like as good as the Chinese support lol. (they will do anything to help) I'm thinking I Might bring in a pallet load to New Zealand and sell them here as shipping by air is so expensive. On Sun, 2 May 2021, 5:09 AM John Dammeyer, <jo...@autoartisans.com> wrote: > > 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 > _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
