Hi Gene, I understand that. But I also know I bought the expensive and theoretically high quality US Digital encoders 10 years ago for my DC servos. Ultimately they were way to sensitive to noise and in fact US Digital discontinued that line for that reason. So I have two useless encoders. I replaced them with CUI and they work better.
My point is what you see on EBAY and AliExpress are not all created equal. The US Digital encoders appeared to work but eventually the UHU Servo drive reported a difference in counts and a move to home was off by a number of encoder edges. Enough to count to a few thousands of an inch. The UHU CPU replacement from Sweden (Henrik Olsson) was a dsPIC and had better encoder support. Even then it still had problems with the US Digital. Not with the CUI. What I'm saying is that when you order an AC servo c/w drive you may find that because they had the lowest price it was low because they used the cheapest encoder. Or maybe the cable they supplied was lower quality. Whether the product is from China, Japan, USA or Germany for example, lower price doesn't equate to the same quality as higher price. The best example so far for me was the stepperonline.com 6A driver that had a 3.6kHz whine on two different stepper motors. Loud enough to be a pain in the ear and cost with PRIME shipping from Amazon was $80 Cdn. A unit from Bergerda with the same specifications and close to the same look ended up with FedEx and Canadian taxes to be $82 each. (I bought 2 for the two motors I had here). No whine. Ribs on the heatsink were twice as high. A few extra features and a metal cover rather than plastic which might even help with electrical noise suppression. And a different size connector for the control signals verses motor/power so no chance of accidentally plugging in the wrong one. So though a lot of units look the same, unless you are buying a STMBL with full source code and schematics and have control over everything including the encoder on the motor the lowest cost unit isn't always the best. I'd still rather buy a MESA board than some cheap clone from China for example. Or if I needed something Jon Elson sold I'd buy from him rather than lowest cost from China. John Dammeyer. > -----Original Message----- > From: Gene Heskett [mailto:ghesk...@shentel.net] > Sent: January-28-21 12:31 PM > To: emc-users@lists.sourceforge.net > Subject: Re: [Emc-users] Fanuc Servos? > > On Thursday 28 January 2021 12:09:00 John Dammeyer wrote: > > > Just be careful and ask the supplier what type of encoder is mounted > > on the servo. There are encoders and there are encoders. My > > http://en.bergerda.com/ servos use a Japanese brand which they claim > > are better than some of the Chinese ones out there but are also > > considerably more expensive. Differential output from the encoder is > > a must have to reduce the effects of electrical noise. > > > > John > > True, but Omron makes differential encoders with up to 1024 ppr, for a > $21 price on ebay. > > I have one with 1000 ppr on the rear of my GO704's spindle motor, turning > faster by 3 or 4x than its rated for, currently driven by a piece of > heat shrink tubing as the elastomer coupling has gone away two years > ago. > > The diff signals are made single ended to drive a 5i25's inputs by a pair > of rs-485 to ttl boards at nominally $2 each on ebay. I had to program > them for 1 way traffic though. So my spindle scale is a bit over 7,000 > in high gear, and a bit over 14,000 in low, and I can use PID_S.Pgains > of 20 or more. > > To say my speed control is stiff is the understatement of the month, I > only know the spindle load is high by the chirping iron in the motor at > around 1.8x its nameplate 9.7 amps courtesy one of Jon's pwm-servo's set > for around 17 amps. Up to that point, no change in the machines noise as > a tap digs in. > > I get my spindles index from a screw silly glued to the side of the > drawbar retaining cap by way of an ATS-667 watching it go by. > > > > > > -----Original Message----- > > > From: andrew beck [mailto:andrewbeck0...@gmail.com] > > > Sent: January-28-21 1:14 AM > > > To: Enhanced Machine Controller (EMC) > > > Subject: Re: [Emc-users] Fanuc Servos? > > > > > > You can buy Chinese yaskawa copy ac servo drives 2.4kw for like > > > 260usd. So it's just not worth it now. I just sold my fanic drives > > > in the end. Its so nice to just bolt on some matched servo drives > > > that just work out of the box. > > > > > > On Thu, 28 Jan 2021, 14:20 Jon Elson, <el...@pico-systems.com> wrote: > > > > On 01/27/2021 11:35 AM, Todd Zuercher wrote: > > > > > How useable are Fanuc's servos and amps with Linuxcnc? My > > > > > understanding > > > > > > > > is that it is very involved to try to force them to work with > > > > anything other than a Fanuc control > > > > I make converters for the two most common types of Fanuc > > > > encoders used on brushless motors. > > > > I also make a digital servo amp for them that can be used > > > > with my PWM controller. > > > > The older "red cap" motors had encoders with standard > > > > quadrature plus index output, but the commutation signal was > > > > proprietary. I have a board that converts the commutation > > > > to industry-compatible "Hall" signals. > > > > > > > > The newer type is serial, but my converter produces > > > > industry-compatible quadrature plus index, plus the "Hall" > > > > signals. Note there are absolute and incremental versions of > > > > these encoders. > > > > The problem with the incremental versions, like (alpha)I64, > > > > is that they are lost when power is applied, so they need > > > > you to crank the motor past the index location by hand after > > > > every power on, before commutation is available. So, these > > > > encoders need power-off brakes and battery backup if the > > > > control is ever turned off. > > > > The absolute version have additional low-res data tracks > > > > that allow the encoder to know the angle immediately at > > > > power-on, so no battery is needed to have commutation > > > > immediately on power on. > > > > > > > > Now, the Fanuc servo amps are more difficult, as about 1984 > > > > they stopped releasing any documentation on their > > > > electronics. So, it is essentially impossible to find any > > > > schematics or connection info for their amps. Most of the > > > > brushless amps take SIX PWM signals per axis, so > > > > the controller sends separate PWM to EACH transistor. This > > > > moves all the smarts to the controller, but it complicates > > > > things a bit. > > > > > > > > Jon > > > > > > > > > > > > _______________________________________________ > > > > 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 > > > 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
