I'd not worry about the fact that the motor is powered with PWM. To the motor, it is just like DC. Motors don't care about volts, only amps. So a 12V battery that is chopped by 50% PWM looks like 6 volts DC even if it is not DC.
If you get to control the PWM frequency set it above what you can hear. 1KHz is an annoying whine but I can't hear 20 KHz. The fact that you can hear it disproves what I just wrote about the motor thinking it is DC. The sound is the motor physically moving. But in terms of output power and speed, the motor does not care. Once I made a fan speed controller but it was hand soldered and a rats nest of wire. It turns out to be an AM radio receiver. (They are surprisingly easy to build on accident) I could hear talk-radio on the fan blades. It worked fine and controlled the fan speed but I could hear radio. Whatever is used to modulate the power going to the motor will physically move the motor. So as said, make it ultrasonic. Model airplane servos are completely different. There the PWM is a control signal and does not modulate the power. It is strictly a control input used to communicate the setpoint from the radio control transmitter to the servo box. About that backlash, that is a good reason to place an encoder on the faceplate. A fun research project would be to use a video camera aimed at the veneer scale as feedback control. Visual feedback is common with robotics but I wonder if it is ever used for machine tools The problem is heat if they over heat they fail. The volt limit is really just a way to limit current. The chip is different and can be damaged by over volts. So that car companies need to over spec by a factor of 2X or 3x On Thu, Oct 15, 2020 at 11:45 AM Gene Heskett <ghesk...@shentel.net> wrote: > Greetings all; > > I've printed the STM docs on this chip, which does leave a gap between > whats on the board and theory. > > 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. > > I did take a peak at the encoder, and it looks to be optical with about > 100 stripes per motor rev. So I'm a bit puzzled that my scope measures > it at 5.4 kilohertz running free on the table. Quadrature looks very > very good, perhaps a 1% timing wobble for either pulse. A mesa encoder > should give a pretty noise free outout. > > That, and the fact that STM characterizes it running in a 13 volt > automotive environment despite its 40 volt rating. Seems to me they are > useing that additional headroom to compensate for some pretty crappy > motors. And I have no clue what this motor looks like with power > applied, along with a 50% pwm while seeing 24 volts on the motor power > input pins. > > 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 > -- Chris Albertson Redondo Beach, California _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
