On Sunday 13 June 2021 17:27:51 John Dammeyer wrote: > > From: Gene Heskett [mailto:ghesk...@shentel.net] > > > > 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... > > Hey Gene, > You're probably using cheap far east parts when you talk about optos.
Well, its what is supplied, in/on what we can buy, both in driver inputs like the 2m542 and its ilk, and in common bob's. The 7 cent parts in reel qty's. And generally speaking, its fast enough to push the motor fast enough its coil inductance gets in the way of ever reaching the labeled on the dip switches current flow, so the torque goes down to zip anyway. The link below is to a GAs led, some of which can easily be driven by a 4 channel encoder for tv fiber interconnections with all 4 channels being full hi def, and its definitely not the 7 cent variety. Probably at least a magnitude higher priced. 94 cents in 1k lots ack the link. At 10 Mb/sec thats slow, good ones can do gigabit+ speeds but aren't cheap. > This one that I use is good to 10Mbps. > https://www.onsemi.com/products/optoelectronics/high-performance-optoc >ouplers/high-speed-logic-gate-optocouplers/hcpl2631v > > And the AM26LS31 differential line driver is also way up there in > speed. And the spec on the Bergerda AC Servo is that it also can > handle that speed. Thats great John. But I haven't noted a ready supply of such speedy parts being used on the boards we CAN buy, with the exception of cnc4pc's C1G rev 4 board which has been discoed as it was about 85 bucks. It also had enough tally leds to light the room with. handy for trouble-shooting too. But cnc4pc no longer makes an equivalent bob, dammit. > I've attached the schematic of my interface board for the spindle. > Note I do use the slow 4N27's for the slow signals like ENABLE and > FAULT. Even the PWM DIR signal which is separate from the STEP/DIR > signals is only buffered with a 4N27 since again the speed for > direction change isn't a big deal. > In my case for the BS1 servo, I used the pwngen in mode 2 and speed was needed as slow=hot chips. > > 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. > > IMHO steppers are really useless above about 750 RPM unless they are > so oversized that the torque drop off above that speed still runs the > machine. > > But I'm _not_ using steppers. AC and DC Servo motors. Don't suffer > from the issues that steppers suffer and wonderfully quiet. Where > before with the GECKO and 1000 oz-in stepper on the knee I couldn't > hear the bevel gears rattling. Now the motor is so quiet the other > noises become annoying. Yup. > Same with the spindle. The large cast iron single phase AC 2HP 220VAC > motor had quite the hum when it was turning. The much smaller 1.8kW > AC Servo is so much quieter and variable speed. I looked into > getting a three phase motor for it and a VFD. The Bergerda > combination ended up being cheaper. But I did have to cast and > machine my own pulleys. Now the noisiest part of the spindle is the > rattling of the spline inside the drive part of the quill. And thats probably created by the servo's response to quantization noise causing motor speed variations that use up the slack. All of that went away when I moved from a 274 edge optical encoder on the spindle, to a 1000 line on the rear of the motor, my scale for the spindle in the ini file is now a bit over 7000 in high gear, and something north of 14k in low gear. And below 400 revs, its so quiet I have to look at the tool to see if its spinning. The index however, still comes from the spindle. > 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
