On 12/5/24 23:29, Chris Albertson wrote:
On Dec 5, 2024, at 2:48 AM, gene heskett <ghesk...@shentel.net> wrote:
They stand up to investigation. No ticklish servo tuning, they simply do as
they are told. The motor has its own encoder that's wired only to the driver.
The error determines the motor currant and that allows them to run lots cooler.
At the same time, if the error goes up, the driver will hit them with every amp
the psu has, skipped steps are history in that they don't happen. Cost over
regular steppers ranges between $40 and $80 per axis. They Just Work.
This is how the motion control world is evolving — lower level control is
migrating closer to the motors. I think one reason is to make the control
loop faster. I don’t know about your motors but 10KHz PID loops are not
uncommon. They might be running close to that.
The link below shows some tiny 2-phase steppers being controlled as if they
were analog BLDC motors. I think this is how you closed loop motors work and
then they wrap a step/dir interface around it.
I don’t know but I think the closed loop “steppers” are not even being stepped.
Today we can drive the 4-wire stepper as if it were a BLCD motor and use FOC
(field-oriented control) By using analog voltages (PWM) on the leads we have
very fine control of the magnetic field orientation and se can smoothly rotate
the field.
I agree with that thinking Chris, but that was not my experience in the
case of my Ender 5 plus and its puny y motor. That would show a ragged
straight line if not dead stopped for y. The jags corresponded to steps
when using a 4 lead nema23 motor geared 1/1 to get from motor to y
shaft, which is now a 25mm cf tube across the rear where the y motor
WAS, with a pair of 40 tooth pulleys from the motor now mounted about 4"
below and inboard driving the right end of that cf tube. So I switched
that nema 23 out and subbed a nema17 with a 16 tooth on it, changing the
rotation_distance to correct the y calibration.
Those jags are still there but now far less than nozzle diameter with
the nema17 spinning 1.5 times faster. On 72 volts it can likely do 4500
or more rpms, This printer now prints text to note the size of the screw
at 150mm/sec, far more readable than it could running at 15mm/sec OOTB,
and no input_shaping in its config. Running at /16 in the drivers due to
the slow opto's in the drivers step/dir interface. W/o those, klipper
claims to be able to drive a /256 stepper, but I have had lcnc get
confused at /32, thread loop too slow even at 2kHZ. Now its the first
printer I've had that /Just Works/, no frozen nozzles ever. cobbled up
direct drive hot end.
I think this is what those closed-loop steppers are doing, they are not
stepping but rather rotating to the next commanded step.
You could find out if you could put an scope on the power leads and record a
half second of waveform.
Here is a demo video of an FOC interfaced NEMA stepper. These are the common
$11 motors you see in 3D printers but it is not being stepped it shows what can
be done for cheap today. The plastic wheels are pressure fit direct the motor
shaft. The entire little machine cost about $50. I’ve linked the best part
of the video but you can rewind and even see the C++ code on screen
I know you might not care about little demo robots, but this shows that these
cheap ’steppers” are capable of much better performance than we think.
https://youtu.be/f9GJqqUpL2w?t=817
Arduino BLDC balancer robot - Tutorial
youtu.be
Stay warm and well.
Cheers, Gene Heskett, CET.
--
"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
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_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
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Cheers, Gene Heskett, CET.
--
"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
_______________________________________________
Emc-users mailing list
Emc-users@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/emc-users
