On Monday 25 January 2016 12:56:41 John Kasunich wrote: > On Mon, Jan 25, 2016, at 12:37 PM, Gene Heskett wrote: > > On Monday 25 January 2016 08:00:12 Marius Alksnys wrote: > > > 01/24/2016 11:55 PM, Gene Heskett rašė: > > > > On Sunday 24 January 2016 16:30:45 Marius Alksnys wrote: > > > >> 01/24/2016 04:37 PM, Dave Cole rašė: > > > >>> Is the positioning ability adequate? > > > >> > > > >> I am impressed how strong it holds in position even when fed > > > >> with DC current (freq = 0). I can't force it to rotate by hand, > > > >> while it is very easy rotating while turned off. > > > > > > > > That motors rotor has to be offcenter enough to drag under dc > > > > exitation, whereas it should move like it was full of cold > > > > molasses. Call a surveyer slow, but dead smooth. > > > > > > > > As that raises the spot heat from friction at low speeds, I'd > > > > want to have a spare on the shelf in case it self destructs. > > > > > > Sorry Gene, it is hard for me understand almost all of your posts > > > without dictionary and deeper analysis of your words.. It might be > > > because my mother language is Lithuanian, my English technical is > > > ~ ok, but your posts are full of colorful English.. :) > > > > And despite having some Iowegian neighbors while growing up, I am in > > the same situation, I don't know a word of Lithuanian. I in fact, > > highly appreciate that you have learned English well enough to write > > it quite well, and I thank you for that effort. And if my posts > > are "entertaining" because of some of the slang phrases I might use, > > that I hope, is a Good Thing. > > > > > This spindle rotates at 10kRPM nicely, thus I have no doubts it is > > > in good balance. I think heavy magnetic field holds the magnetized > > > rotor almost in place when I turn 10A DC current on. > > > > If its not perfectly centered between the field poles, the magnetism > > will pull it farther off center, flexing anything in the assembly > > that can be flexed, far enough to drag on and stick to the poles. > > Some assumptions are being made here. Gene is assuming that this > is an induction motor, which as he says should experience a smooth > resistance proportional to speed when there is DC in the coil. I find > it hard to believe that the motor would be so far off-center that it > could start dragging. (I'm also making an assumption - that Marius's > 10A DC current is within the motor rating.) > > Another explanation could be that the motor has a permanent magnet > rotor. Such a motor doesn't slip. Under DC excitation it acts like a > stiff spring. Again I'm assuming 10A is within spec, and that rated > voltage is 230 or more, not some little 24V thing. That means it's a > pretty decent sized motor, and the "spring" is quite stiff indeed. > It could easily be impossible to turn by hand, especially if there is > nothing but a shaft to grab.
Quite true John, and something I neglected to consider as I was rather convinced it was an induction motor that Marious had. But if a PM armature, it becomes a synchronous up to its load ratings at that rpm, and synchronous at DC is pretty well locked in position. Thanks for pointing that out. Now if Marius can clarify by asking the driver to go 5 rpm, and getting 5 rpm exactly. Or driving it temporarily with line frequency power while watching it under flourescent lighting. If the blur is stationary, it is a synchronouse motor. If not, the blur will be drift CCW at whatever the slip angle is. 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> ------------------------------------------------------------------------------ Site24x7 APM Insight: Get Deep Visibility into Application Performance APM + Mobile APM + RUM: Monitor 3 App instances at just $35/Month Monitor end-to-end web transactions and take corrective actions now Troubleshoot faster and improve end-user experience. Signup Now! http://pubads.g.doubleclick.net/gampad/clk?id=267308311&iu=/4140 _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
