On Friday 16 October 2020 12:26:11 John Dammeyer wrote: > > From: Thaddeus Waldner [mailto:thadw...@gmail.com] > > Perhaps a more significant advantage of the servo drive described by > > John Dammeyer is that it has a current control loop running inside > > of the LinuxCNC velocity control loop. > > Pretty fancy to do that on an 8-bit microcontroller. That ATTiny has > > an on-chip analog comparator. > > > > > On Oct 15, 2020, at 10:03 PM, Jon Elson <el...@pico-systems.com> > > > wrote: > > > > > > On 10/15/2020 09:49 PM, John Dammeyer wrote: > > >> The theory is that if the PWM signal is high the H-Bridge is > > >> switched to say turn the motor clockwise. If the PWM signal is > > >> low > > > > the H-Bridge is switch to turn the motor counter clockwise. > > Therefore with 50% the motor is first asked to turn one way and then > > the other. That results in the motor essentially being locked in > > place. Change the PWM on either side of 50% and the turns in the > > subsequent direction. > > > > > This is called synchronous antiphase. The advantage is there is > > > no dead zone around zero. The DISadvantage is it causes a > > > triangle-wave current in the motor which can be quite substantial, > > > and causes excessive heating of the motor and power transistors. > > > > > > Jon > > And building these isn't as easy as it may appear at first sight. I > bought a couple of UHU boards from a company called > embeddedtronics.com (no longer around now) that didn't work. They had > tried to shrink down the design too much and encoder noised and motor > noise caused unreliable motion. > > Here's one of the early threads (2004) on the UHU. > https://www.cnczone.com/forums/open-source-controller-boards/14217-cnc >-software-forum.html > > For high power circuit layout is everything. Especially for EMI > suppression. And servo motors can generate a lot of EMI. I think > that's why Gene was talking about inductors in series etc. > > John Dammeyer > Thats part of it John. The "ripple" currents can be quite substantial if the pwm frequency is too low. And at 10 KHz tops on the STI chip, I am concerned with that and the headaches I can get near ultrasonics enter into my worries. Even an ultrasonic burglar alarm, singing along at 44 kilohertz puts a high pressure feeling in my ears. Very uncomfortable even if I can't "hear" it.
Thanks. 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 Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
