Thanks for the replies. I adjusted the current, initially by measuring the reference voltage to get (from memory) 150mA. That ended up warming the motor too much, so I reduced it some more. Regardless of the current, the behaviour didn't change.
I do have some TMC stepper drivers around, I should see if that works. I will end up replacing them with a geared version - same motor, but with a small gear box, so full/half stepping might not be an issue. Frank -----Original Message----- From: Gene Heskett [mailto:[email protected]] Sent: Friday, 19 March 2021 12:53 PM To: [email protected] Subject: Re: [Emc-users] OT: Driving tiny steppers On Thursday 18 March 2021 18:29:50 andy pugh wrote: > On Thu, 18 Mar 2021 at 20:52, Frank Tkalcevic > > <[email protected]> wrote: > > Is there anything special about driving these motors? > > I guess that as they are 20-step motors it is a long way between the > poles, and microstepping relies on finding an elastic equilibrium > between poles. A lot of that can be blamed on the poor co-operation between the motor makers and the driver makers resulting in very poor mapping of the currents delivered, to the magnetic characteristics of the motor, and I have noted that the fine microstepping performance can and usually is, related to the ideal current ratios for the individual motor, due to the non-linear magnetic performance of the iron with improved performance in terms of degrees/step often obtained at less than full motor currants. But for a 20 step motor, if I needed fine results I'd gear it down to get the accuracy needed and drive the motor at no more than half step. What I have observed is that you can get decent results from a 2M542 driver at a little over half the max current, at a /8 or even /16. Swap that driver for a DM860 and its so much poorer, that there is no optimum current, even at a /32, its essentially a half step motor in terms of how far it moves for one step. And it hammers a nema34 something awful even running at a /16. I know little about the A-4988, but its predecessor, A3977 used on the 3 & 4 axis boards from another board maker isn't that good either. YMMV of coarse, a lot at times. > I think that it is often like you describe, just rather less obvious > on a 200-step motor. 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) If we desire respect for the law, we must first make the law respectable. - Louis D. Brandeis Genes Web page <http://geneslinuxbox.net:6309/gene> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
