Thanks for the ideas Gene. John -----Original Message----- From: gene heskett [mailto:ghesk...@shentel.net] Sent: June 25, 2023 7:25 AM To: emc-users@lists.sourceforge.net Subject: Re: [Emc-users] Drilling holes in the back of a stepper motor
On 6/25/23 05:32, John Dammeyer wrote: > The problem is the rear shaft isn't that long. > > I went through the process of considering an adaptor plate that fastened to the 4 holes. There may be a fancy way of making a thick plate with a thinned area just for the encoder mount. But it would have to have a stud protruding away from the back and then a nut. The plate can't be thick enough to hold both the encoder and threads for screws and still have the encoder disk mount to the back shaft. > > The alternative would be to press fit on a shaft extension and then use the stepper motor to turn the extension to be symmetrical with the axis of the motor shaft. Then I could use a thicker mounting plate. > I faced a similar problem when I moved the homemade optical encoder on my g0704 mill from the spindle to the motor, which had no back shaft at all as it sits flush in the rear housing cap of that 1hp motor. So a very carefully drilled and tapped for about a 3mm screw in the motor shaft and made a 20mm long brass extension. Then put the elastomer coupling that came with the 1000 line 22 dollar Omron encoder on standoffs drilled into the decorator cover with over sized holes so I could align it as best I could, It ran that way for about a year, but demolished the coupling eventually, so now for around 5 years the coupling has been two layers of heat shrink tubing shrunk on in place of the coupling. I've not had to replace either the heat shrink or the encoder since. With that much higher resolution, quantization noise is gone, Pgains in the motor control PID can be as high as 40 w/o oscillation. Of course theres some hal trickery to make it all just work, like changing gears with the motor running. I have 2 tally switches on the gearshift knob that are only activated if the thing is fully engaged in one or the other gears. By way of a mux4 they switch the scale so the spindle rpm tach is dead accurate but if its not fully engaged, neither switch is true, so the mux4 feeds a tickle signal to the motor so the motor is turning around 50 rpm between gears, so I don't have to grab the spindle and turn it till the gears engage. I can be spinning at 1500 revs in low gear, reach up and crank the knob, the motor is down to a crawl as soon as the knob moves a couple degrees, the motor then engages the other gear w/o hesitation, as when the tally switch makes for that gear, whatever speed was selected is restored and the tach says 3000 revs. Motor response is in the 100 millisecond range, I can't turn the knob anywhere near fast enough to cause a gear clash. Works in fwd and rev from m3 to m4 or for rigid tapping in 2 maybe 3 hundred milliseconds. Some of that key is the power supply for the motor is about 125 volts, AND Jon Elson's pwm-servo controller being a full 4 quadrant controller, so when the motor is slowed that fast, the psu voltage peaks at around 170 because the motors spinning energy is sucked out of the motor and back into the psu, charging it up to around 30 volts more than the capacitors voltage ratings, but this over voltage is then used up by feeding it back into the motor to speed it up in the other direction. So that 90 volt rated motor is being drasticly abused. And it is still running on the oem brushes yet in 2023. Instant horse power for rigid tapping is at least 3hp. 9.7 amps is its FLA, but Jon E's servo current limits at 18 amps. The PID is stiff enough the squeaking of the iron in the motor is my only indication the load is too high. > Or, given that the motor drives a 25:1 planetary gear and I'm really only interested in tracking motor revolutions and detecting stall conditions (hence quadrature) I could likely get away with a custom disk and some slotted sensors too. Also more complicated to build. And likely full of quantization noise. I thought the bearings were going out of the gears from that noise before I changed the encoder. Now it runs silently below 500 spindle revs. > > Trying to keep it simple and the easiest is to have the encoder screw directly to the back of the motor. However with StepperOnline motor by the time it's here in Cdn $ it's over $100. So I can take the risk and drill holes in the back. Or get creative with other approaches. Precisely why I suggested the 3d printer solution. An Omron 1000 line encoder will be longer than your pix'd encoders but for $22 USD and some time to print the adapter stuff, be a very workable solution. You can essentially duplicate the new stepper/servo's by just changing the controller but its still a bit high, the Hanpose cl57 controller is around $80/copy from aliexpress if you can tolerate the shipping delay. The huge advantage of the new tech stepper/servo is the motor current is controlled by the error, so if the motor is working easy, it runs dead cold, you aren't burning up the power meter sitting there with full power on a motor regardless of load. Because stepper accel and top speed is controlled by the available motor voltage the old std of a 42 volt supply with a 50 volt rated 2m542 rated driver is gone, the cl42 for nema 17's and the cl57 for nema-23-24's is now rated at 90 volts. Imagine what you can do with a stepper when you've got 80 volts to bang on it. The PSU people haven't caught up with that yet, but 48 volt 600 watt cheap supplies, which can speed up a stepper about 4x quicker than they can at 24 volts are now available from many sources. I look for 70 to 80 volt kilowatt supplies to be under $45 USD in another 6 months. Supply will catch up with demand. Take care and stay well Jon D. > John > > > -----Original Message----- > From: andy pugh [mailto:bodge...@gmail.com] > Sent: June 25, 2023 1:57 AM > To: Enhanced Machine Controller (EMC) > Subject: Re: [Emc-users] Drilling holes in the back of a stepper motor > > On Sun, 25 Jun 2023 at 04:31, John Dammeyer <jo...@autoartisans.com> wrote: > >> Is there any reason I can't clamp the motor in a vice and pop in two holes >> and tap them with a bottom tap at the spacing of the mounting flange? > > I have done it in-situ, but there really isn't all that much metal in there. > > I think pulling the back cover off (leaving the rotor in place) and > choosing your mounting point carefully would probably be best. > > Or, as Gene says, use the existing holes, very short screws, and an > adaptor plate. > > > > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > 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. 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