On Wednesday 01 March 2017 22:08:50 Kurt Jacobson wrote: > Since there has been a significant amount of discussion about the > cheap MPGs I decided to take mine apart and find out how they work. I > took a bunch of pictures during the disassembly, you can find them > here: https://goo.gl/photos/w8fJaFLzzUsFzfmV7 >
Most interesting Kurt, and thank you very much. And I have never felt a mechanical detent as smooth as these without using contactless magnetics. So I sit corrected. Thats truly amazing grease, but for how long will it maintain that "feel". What sort of bearings if any does the shaft spin in? Oh wait, I think I saw some "oilite" sintered bronze. Still, that looks like very good construction, worth more than we paid. What sort of an inspection tool with a radioactive sign on it were we looking at, along with its scintilator pulse outputs on the scope? That also looked interesting. > It turns out that they use a simple flat spring and "roller" that > falls into grooves in a small wheel for the detent action. The pulses > come from an optical encoder with metal disk. > > They are well made considering the cost and I don't think they are > overstock. I bought this one from ebay for $16 and free shipping. It > looks the same as the MPJ ones. > http://www.ebay.com/itm/251710166569?_trksid=p2057872.m2749.l2649&ssPa >geName=STRK%3AMEBIDX%3AIT > > Regards, > Kurt > > On Wed, Mar 1, 2017 at 8:55 PM, Gene Heskett <ghesk...@shentel.net> wrote: > > On Wednesday 01 March 2017 07:42:17 Roland Jollivet wrote: > > > I had always assumed that machine MPG's generated one state change > > > per click, but following Gene's discussion, I pulled out my 1988 > > > Fanuc MPG, and saw that it was also 4-states per click. Obviously, > > > one 'pulse'/detent > > > > > > Does anyone know the rationale behind this? > > > I assumed one always wants one step per click, so why not use a > > > 25ppr encoder and use every change? > > > > because its relaxed condition is always the same in terms of the A/B > > logic outputs, the detent, mechanical or magneticly derived, assures > > this condition by steering it to tat condition when you've let go of > > the wheel. Yes, the encoder does see 4 edges go by, but that is one > > complete detent, therefore the encoder is told to produce a count > > output divided by 4, so you get a 1 count advance per detent. > > > > > Used as currently is, it would have to be a software /4 to be > > > useful. You could also do a /2 or /1, but no-one ever wants a x2 > > > or x4 on their MPG It's always x10, x100 or whatever, so the > > > count/detent would always have to be n/4 x 1 .. or.. n/4 x10 in > > > software. > > > > I suspect this choice is more a force of habit, hence what I am > > doing give more choices, with no step being more radical than a > > 2.5/1 rate. The gain progression is 1,2,5,repeat for next decade, > > and the 1,2 sequence of the 3rd decade. 8 choices, the last being > > quite fast with the possibility that the joints MAXVEL may limit it > > depending on how furiously the knob is spun. On my machines I'd bet > > on it. :) > > > > > Alternatively, if I was going to make my own MPG, surely I would > > > just make a 25ppr encoder and make it 1 detent/change? > > > It's far easier for me to make, so surely it would have been for > > > Fanuc too? > > > > I've not dissed one of these, but since they need power, and the > > friction is vanishingly small, so as a CET I have to assume that > > they are hall effect sensors similar to the AL667's working on a 100 > > tooth cogwheel, with a stronger magnet actually supplying the detent > > force external to the bias magnets in the AL-667's. > > > > Yes, one COULD make a 25 ppr wheel, but you would have to use two > > cogwheels, a coarse one for the logic, and a 4x finer wheel to > > supply the detent. And you sure as tootin can't do it for $20 worth > > of your time and tooling. > > > > The hall sensors with their bias magnets do supply a small detent > > force too, but there is more than 1 stable condition given a low > > enough friction/stiction to its movements. Just the weight of the > > spin knob could cause it to move w/o the extra much more positive > > acting magnetic detent acting on another section of the rim of the > > same 100 tooth cogwheel. > > > > These spin dials are quite well made, and I don't believe could be > > made in China for a $20 bill even in 10k quantities. They have to > > be from a liquidation sale. > > > > So when these surplus units are gone, we'll likely never again see a > > competing, usable product for less than $50, likely more. If you > > have a potential use for them, grab a lifetime supply right now. > > > > > What am I missing? > > > > See above Roland. > > > > > Regards > > > > To you too, Roland > > > > 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 > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ---------------------------------------------------------------------- >-------- 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 > 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) 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
