On Sunday 13 June 2021 14:43:00 John Dammeyer wrote: > At the moment I still have the stepgen 5 on the second parallel port > so I can measure both PWM and STEPPING. > > Raspberry Pi4 + 1GB + LinuxCNC + MESA_7i92H + ProbotixBoB + custom > VHDL for the MESA board thanks to Peter Wallace at MESA. > > AXIS display shows 1500 RPM, PWM is 50% and if I zoom in on the step > pulses my scope tells me it's 250kHz which is 50% of the max step rate > as currently set.
BBBuuutt, 250 khz is right at the ragged edge of what the opto-isolators in the input of most stepper drivers can pass. If you want maximum speed, cut the drivers divisor in half at the dipswitches, and cut that axis's scale in half for the same motor speed at half the step rate... > Math for that is 2500 line encoder = 10,000 edges per revolution which > at 3000 RPM is 50 RPS. And 50 x 10,000 = 500Khz step rate. Well above what the average bob can pass. And 3k rpms is pushing a stepper too fast for anything but laying loose on the table. if you want real, usable torque, stay below 1500 revs. Maybe 2000 but only with a 48 volt supply on a 50 volt rated driver. I turn my 48's down to 42.5 just so the driver has some headroom before it breaks the mirror and lets out the smoke. Again, that is only valid if there are no opto or other noise suppressing capacitors in the bobs input circuits. I've had to modify nearly every bob I have ever used to bypass the opto's or remove the noise filtering, even the opto-less sainsmart 5 axis bob has had to be modified by removing the grain of sand capacitors in the inputs connected to the encoder in the motor for my A axis servo. > The encoder on the spindle will have less lines and likely I'll > program the Bergerda Servo to divide the encoder by 5 to bring my step > rate for the spindle down to 100kHz. It's differential drive out to > the Bergerda so I'm not too worried about noise. > > Power tapping here I come. Baby steps. > > John > > > -----Original Message----- > > From: John Dammeyer [mailto:jo...@autoartisans.com] > > Sent: June-13-21 1:35 AM > > To: 'Enhanced Machine Controller (EMC)' > > Subject: Re: [Emc-users] Spindle control > > > > So here's the photo with the Pi4 1GB running LinuxCNC. The 4 roller > > switches are the three homes and the shared limit for the other > > axis. Normally there would be 3 in series. The orange paddle > > switch is estop. The cable to these switches goes to the 7i92H > > P2.DB25. > > > > On the P1 connector I have the Probotix BoB. No isolation needed > > for testing so it's powered from the same supply on both sides. I > > have the scope on Pins 2,3 of what would be the second DB25. > > > > Now if I plug a motor into the step/dir outputs of the BoB it should > > spin the motor based on requested spindle RPM. > > > > Been a good day. > > John > > > > > -----Original Message----- > > > From: John Dammeyer [mailto:jo...@autoartisans.com] > > > Sent: June-13-21 1:05 AM > > > To: 'Enhanced Machine Controller (EMC)' > > > Subject: Re: [Emc-users] Spindle control > > > > > > No worries. Found the solution. > > > I have spindle.0.speed-out-rps connected to spindle-cmd which > > > ends up being a signed float. > > > > > > net spindle-cmd <= spindle.0.speed-out-rps > > > > > > And that's connected to the stepgen > > > net spindle-cmd => hm2_7i92.0.stepgen.05.velocity-cmd > > > > > > Results in my P1.19_DB25.2 showing a square wave on the scope when > > > I toggle the axis CW and click on the speed. Change to > > > > CCW > > > > > and click speed again I get the square wave on the scope and the > > > P1.23_DB25.3 changes to a logic high for a change in direction. > > > > > > More when I test it with a motor. > > > John 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
