On Monday 13 July 2020 22:44:37 R C wrote: > well, I can calculate what the speed needs to be, also I can actually > "observe" it too.. by pointing the telescope at a star and see how > much the deviation is. I have encoder to check the actual speed of a > shaft. > > I found some information in a manual/tech-sheet that comes with the > drivers, so I am trying to figure out what the best stepping rate is > and what the best way of actually sending pulses to the stepper-driver > is. > > I wrote some c-code that runs the motors in pthreads, I just want to > know what the best way is. pulse lengths, pause/gap length etc. > (basically the best way to use a dm542 (all those steppers are sorta > the same I understand) > > The driver tech-sheet basically says it can do pretty all it's > available micro stepping with a 1.8 degree stepper motor, I wonder if > that is really true. > In theory yes, in practice, no. There is resistor tolerances and all sorts of errors that can creep into a motor being held by the relative balance of the currents thru 2 sets of coils. So while a full switch will move it 1.8 dgreees, or 1.2 with the newer 3 phase models, between magnetics and parts tolerances, half current in each coil might be out of balance as much as 10% in off the shelf stuff. Sometimes its fairly obvious, I have a dm860 driver that when moving a 1600 oz/in motor at a /8 divisor, moves 7 steps rather noisily, and the 8th step cannot be seen or heard. Worked fine on my mill as long as I stayed below 26 ipm. But thats too slow for rigid tapping. A 960oz/in and ac powered driver was subbed, moves that heavy head at nearly 100 ipm, dead smooth.
> Ron > > On 7/13/20 8:35 PM, Chris Albertson wrote: > > A fast control loop that drives each motor at a given speed and a > > second slower control loop that figures out what that speed should > > be. The second loop typically uses "PID" even if only in fact the > > "P" is used. > > > > That can be used to drive any number of motors all at their correct > > speeds. > > > > On Mon, Jul 13, 2020 at 7:28 PM R C <cjv...@gmail.com> wrote: > >> Interesting, > >> > >> > >> but I already have the motors, and the gears are on their way. > >> What I was really looking for is how to drive the stepper-drivers, > >> he DM542 series ones. > >> > >> > >> Ron > >> > >> On 7/13/20 7:53 PM, cogoman via Emc-users wrote: > >>> I recently discovered geared stepper motors. > >> > >> http://www.zyltech.com/nema-17-stepper-motor-geared-planetary-gearb > >>ox-1-7-a-3-1-nm-435-ozin/ > >> > >>> I've been happy with zyltech in the past. I bought one of these > >>> for evluation, but the specs seem to be great for CNC. Low enough > >>> current to work with a stepstick, High enough torque for a fairly > >>> powerful machine, and less than 4 mH inductance should let it step > >>> pretty fast. > >>> > >>> 5.18:1 gear ratio should reduce that 4 meter spur gear, but the > >>> link below has higher gear ratios that would reduce that spur gear > >>> greatly! Backlash could be a problem for CNC, but if you are only > >>> going one way, the less precision gearboxes might be fine. > >> > >> https://www.omc-stepperonline.com/geared-stepper-motor/?sort=p.pric > >>e&order=ASC > >> > >>> Once you visit the stepperonline web page you know as much about > >>> them as I do, but their offerings might be just right for your > >>> application. > >>> > >>> On 7/9/20 2:23 PM, R C wrote: > >>>> Hello, > >>>> > >>>> this is (probably) off topic, been seen that happen. If it is > >>>> please ignore it. > >>>> > >>>> > >>>> I am building a "motorized" telescope mount (dobsonian) with > >>>> what is called an equatorial platform, it has 3 axis which I am > >>>> going to drive with stepper motors. > >>>> > >>>> > >>>> The stepper motors I use with a stepper driver, those common > >>>> DM542 ones, the stepper motors themselves are 2A and 1.8 degrees > >>>> per step. > >>>> > >>>> > >>>> What I want to accomplish with the equatorial platform) (it > >>>> compensates for the rotation of the earth) is that, the start > >>>> and end position accuracy is not that important, smooth and > >>>> constant/consistent movement is. for the azimuth/altitude > >>>> precision is not a really big deal, but you'd want to move these > >>>> 2 axis somewhat swift. > >>>> > >>>> > >>>> So there are a few factors to decide. > >>>> > >>>> > >>>> I probably want micro stepping, what settings on the driver for > >>>> pulses per rev, is best to use (or is that just trial and error?) > >>>> > >>>> > >>>> As with PWM itself, I am probably just not too familiar with it. > >>>> From what I understand, the voltage I use for the motors > >>>> determines how fast I can go (I am going to use a 48V switching > >>>> power supply). > >>>> > >>>> > >>>> as for PWM, I can of course change the length of the pulse > >>>> itself and, independently, change the time between two pulses. > >>>> What is the relation ship there? WHat does a longer width of > >>>> the pulse itself do? and what exactly does a longer gap between > >>>> the pulses do (of course the wider the gap between two pulses the > >>>> slower the motor turns). > >>>> > >>>> > >>>> for, especially, the equatorial platform, I want to avoid > >>>> "jerking" it, meaning starting and stopping the stepper motor > >>>> as little as possible and just go at a 'slow' constant speed. > >>>> > >>>> > >>>> > >>>> sorry if totally of topic.... > >>>> > >>>> > >>>> thanks, > >>>> > >>>> > >>>> Ron > >>>> > >>>> > >>>> > >>>> _______________________________________________ > >>>> 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 > > _______________________________________________ > 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. 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