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.
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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, 1940)
If we desire respect for the law, we must first make the law respectable.
- Louis D. Brandeis
Genes Web page <http://geneslinuxbox.net:6309/>
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