I recall reading somewhere, and I can't remember where, that it's possible to damage a stepper motor by running too much current through them. Not because of overheating, (although that's a possibility), but because the larger magnetic field produced by the increased current demagnetizes the magnets.
In fact, as I recall, removing the rotor from the motor also results in a loss of magnetism and once re-assembled the motor no longer has the same torque. It's possible, although I've no direct evidence for this, that once the motors are assembled the motor shaft is locked is a specific position and then a large pulse of current through the windings is used to magnetize it. The motor frame then acts as a 'keeper' for the magnets. Remove the rotor and some of the magnetism is lost. But I'm not sure about that. For this rotary table I'd do what I did for my lathe. Create an adaptor to hold an arm of say 12". Set it horizontal and then hang weights from it until the arm starts to move. That's the amount of torque required to overcome static friction. Say it takes a 1 pound weight. Then you know you need a 1 ft-lb motor. Look at the torque curves for motors and pick one that maintains the torque you need up to the RPM you want to run. Kinetic Friction is always less than Static Friction so the motor will be correctly sized. I did that for my Milling Machine Knee. With a Gecko and the 1200 oz-in motor and 3:1 reduction the motor moves the knee with both vice and rotary table weight up to the point where the torque curve on the motor starts to drop off. As long as I stay below that speed the Gecko runs the knee very nicely. I did cheap out and try a 600 oz-in motor with series winding arrangement in order to stay under 3A but I could never get the speed I wanted. Hence the Gecko, the 1200 oz-in and 6A. John > -----Original Message----- > From: Chris Albertson [mailto:[email protected]] > Sent: November-26-17 7:43 PM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] temp rise allowed on steppers > > 150F is on the hight side but not above the limit. Keep it under 200F or 100C > > Why not reduce the current limit until it stops working then turn it > backup. Run it just above the lowest current setting that still > works. This will cost nothing. > > If it ever fails you might want to replace it with something else, A > couple options.. > > 1) What you may need to do is find a motor that is a better match to > the load. Then it can run without having to work very hard and run > cooler. > > 2) The other option, more expensive is the now closed loop steer > motors. These use an encoder in the stepper motor that connects to > the driver, so you'd need to replace both bt it uses only enough > current to make motor step. They run much cooler > > > > > > On Sun, Nov 26, 2017 at 2:35 PM, Gene Heskett <[email protected]> > wrote: > > Greetings all; > > > > I have the psu and a 2m542 driver about half wrapped so I can power it > > and run it with a function generator. To get it to drive that table > > which has considerable drag to help hide the backlash, so in order to > > get a decent turn rate, in the 30 degrees/second rate, I've given it 3.7 > > amps, probably a bit much for what I think is a 250 oz/in nema 23 motor. > > > > Them temp rise is about 80F, or about to 150F in a 70 degree environment > > after running steadily for an hour. > > > > If I enable the half power when stopped function, I can't see as that too > > hot given its running duty cycle. Stopped power is half current, or 1/4 > > of the heat generated at full song. > > > > Does anyone else have an opinion? Unmarked motor, bought with the > > original xylotec board and 3 motor kit in the later 90's. > > > > ============================ > > > > The different BoB will be here in another 25 or so hours, at which point > > I'll hook it up when I change the bob for a much faster one. No opto's > > on this one. > > > > 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 > > [email protected] > > https://lists.sourceforge.net/lists/listinfo/emc-users > > > > -- > > Chris Albertson > Redondo Beach, California > > ---------------------------------------------------------------------------- -- > 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 > [email protected] > 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 [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
