On Sunday 19 April 2015 10:22:40 Karlsson & Wang wrote: > Motor torque depends on current. Then increasing acceleration torque > will also increase but how much depends on the inertia, there > rotational inertia and the mass moved. It is also possible there are > some viscous load which depend on speed of motion or rotational load. > I assume current will increase but how much I have no idea. > > Electric motor generate a back EMF which depend on rotational speed so > there is less voltage left to increase current/torque at high speed > and more available voltage left to decrease speed. > > Here > http://en.wikipedia.org/wiki/Brushed_DC_electric_motor#Torque_and_spee >d_of_a_DC_motor the voltage balance and torque equations a little bit > more than half way down in the document is incredibly good knowledge > if working with servo motors. It is also useful to think about this > equations then working with other types of electric motors. The > equations are actually so important i think it would be a good idea to > include them in the Linuxcnc manual maybe in the integrator chapter > and I could provide some help if I have enough time.
We are slightly at odds Nicklas. You are talking servo's correctly, and I am talking steppers. These are different critters. The servo's you refer to will allow a small error and catch up when they can, which may or may not wreck your part depending of the tolerances. Steppers OTOH, will stall under the same conditions, wrecking the part and likely breaking the tool too when the direction reverses at the end of that move So one has to be quite considerably more cautious, even paranoid, about how much you ask of them in the speed ranges where the torque to stay precisely on the path may be iffy, particularly in a complex part that may be quite a few loops thru the code to do the depth the job needs. One of those consideration is available spindle horsepower, as in lack thereof, its a 200 watt motor! I intend to switch it out at some point, putting the 400 watter I took out of the lathe in its place, making it a 2 speed range belt drive when I do, all of which I will have to design & make. It, for some jobs, needs both 5x the rpms to get above any framing resonances and a higher feed rate just to enhance the tool life by cutting deeper into cooling wood when I am carving wood. The wood, if the tool is sharp, doesn't burn, but the bit can turn straw colored occassionaly. But thats off topic and I haven't really started on a design for that yet. The higher voltage psu and a 5i25 card I just ordered are this springs project. The motor is a different critter. > Regargs Nicklas Karlsson > > > > On Sun, 19 Apr 2015 05:55:31 -0400 > > Gene Heskett <ghesk...@wdtv.com> wrote: > > On Sunday 19 April 2015 02:58:14 Karlsson & Wang wrote: > > > Increase in speed should almost certainly be 48/28 faster. I think > > > this is true for acceleration to. Then you just have to hope for > > > the electric motor to tolerate the higher voltage and for the > > > mechanics to tolerate higher speed/acceleration. > > > > Humm, I would have to assume that since the motor currents would not > > be similarly increased, that the accels, wouldn't be enhanced by > > anywhere near that same ratio. > > > > The motors ultimate torque shouldn't change, just the speed at which > > the torque falls off due to inductance? > > > > At present I do not believe the applied accels are modulated in the > > TP to be slower at the higher motor speeds where torque is falling > > off, so we need to use an accel it can handle in spite of the > > falloff. This costs us time at the lower speeds where there is > > generally plenty of torque. > > > > IMO, the accel should be applied with something that looks like a > > t=rc time constant mapping, but that would not be optimum for the > > needed decel since that would start a new t=rc curve, a fast slowing > > at an rpm point where the torque is not available. > > > > Experimentally I have found I can move the existing setup at 22 ipm > > in the range where table weights are well balanced if I use really > > slow accels like 2 seconds or more to top speed. But for anything > > like decent accel settings, I'll stall at 10 ipm or less so I > > generally use sub 10 ipm moves now. One of the reasons for kicking > > the motor voltage up closer to the limits of the drivers, 50 volts > > in the case of the 2M542 driver. > > > > > Nicklas Karlsson > > > > Thanks Nicklas. At least I have a starting point now for how much > > faster I can go. I got the new psu mounted with cooling arranged > > yesterday, but not hooked up yet. > > > > 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> > > > > -------------------------------------------------------------------- > >---------- BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM > > EDT Develop your own process in accordance with the BPMN 2 standard > > Learn Process modeling best practices with Bonita BPM through live > > exercises > > http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- > > event?utm_ > > source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_ > >SF _______________________________________________ > > Emc-users mailing list > > Emc-users@lists.sourceforge.net > > https://lists.sourceforge.net/lists/listinfo/emc-users > > ---------------------------------------------------------------------- >-------- BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT > Develop your own process in accordance with the BPMN 2 standard > Learn Process modeling best practices with Bonita BPM through live > exercises > http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- > event?utm_ > source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_SF > _______________________________________________ > 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> ------------------------------------------------------------------------------ BPM Camp - Free Virtual Workshop May 6th at 10am PDT/1PM EDT Develop your own process in accordance with the BPMN 2 standard Learn Process modeling best practices with Bonita BPM through live exercises http://www.bonitasoft.com/be-part-of-it/events/bpm-camp-virtual- event?utm_ source=Sourceforge_BPM_Camp_5_6_15&utm_medium=email&utm_campaign=VA_SF _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
