> On Oct 15, 2020, at 5:20 PM, Gene Heskett <[email protected]> wrote: > > On Thursday 15 October 2020 17:17:59 Thaddeus Waldner wrote: > >> The reactance and inductance questions are above my pay grade and I’d >> be happy to hear someone explain it. :) I use these for robotics class >> in place of the old BJT L298, which are optimistically rated for 2 >> amps but have more than 2v drop at much less than that current. >> >> Maybe I don’t understand your comment but I’m pretty sure that a 50% >> duty cycle PWM waveform will run the motor at half-voltage. > > What I had in mind was a quicker than hal's logic can do it, as hals > direction reversal by controlling the inA and inB inputs will be plenty > slow enough to have it oscillate possibly uncontrollably. This may not > be the ideal device, we'll have to see once they arrive, which could be > as early as Monday.
The timing specs indicate a Minimum 300 us, typical 600 us and maximum 1800 us delay when switching directions. 600us would be a bit more than half of the 1khz servo loop delay. I’ve never run a closed-loop servo from LinuxCNC, so I have no idea what the consequences of that are. > What I have in mind is basically a 400 watt or more, class D audio > amplifier. Maybe I've gone looking using the wrong search terms. Yes > and with very similar pricing, a dual 2kw is $25. I'm thinking... > >> You command the direction with INa and INb according to the Truth >> Table. The PWM signal will then switch either the A or B low-side >> FETs, depending on the INa/INb configuration. >> >>> It would appear that when enabled, and lets say with a pwm frequency >>> near the top of the 10khz range, that a 50% duty cycle pwm waveform >>> would be the equ of a balanced, at rest servo, so my first question >>> is how much additional inductance in series with the motors leakage >>> reactance will be needed to protect the chip from the current surges >>> at the pwm waveforms transition points? >>> >>> My hal file will obviously need to stage an initial enable at the >>> 50% duty points, then let the pid output thru. >> >> _______________________________________________ >> Emc-users mailing list >> [email protected] <mailto:[email protected]> >> https://lists.sourceforge.net/lists/listinfo/emc-users >> <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) > 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 > <http://geneslinuxbox.net:6309/gene>> > > > _______________________________________________ > Emc-users mailing list > [email protected] <mailto:[email protected]> > https://lists.sourceforge.net/lists/listinfo/emc-users > <https://lists.sourceforge.net/lists/listinfo/emc-users> _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
