On 4/5/24 06:57, Curtis Dutton wrote:
Hello all,
I'm starting a new project to build a motor drive based upon igbt modules.
Hoping to build something that has a single type of controller that will
plug and play with various capacity igbt modules for various size motors.
This thing shall be able to act as either a vfd or servo drive.
Some thoughts from a CET to consider here Curtis.
In my quest for similar functions I first stumbled over a 3 phase drive,
several of which are now in service here. The same technology has in the
last year or so come to the usual 2 phase stepper. I now have 5 of the 3
phasers in service in the garage, two running my 11x54 Sheldon lathe of
1940's vintage, 2 running the B and Z on a 6040 mill and one 1 doing
duty as the A axis on my GO704, which 3 more scheduled to replace the 2
phase stuff currently moving the GO704. The A & B axis are 3MN rated,
motor is driving an rvs series 5/1 worm for a rotary, giving me up to
500 rpm A or B axis with an angular accuracy good enough to carve 2
start vise screws out of hard maple, or hob gears I can't print. For
<$100/axis in sizes small enough for 3d printers, or under $150 for the
bigger stuff, they simply cannot be beat.
They give steppers the accuracy of the microstep or the accuracy of the
optical encoder on the rear of the motor. Which ever is lower.
1. The error magnitude controls the motor current. Low error means low
current, motors run considerably cooler, a saving you can actually see
in the power bill.
2. Because the motor current error controls the motor current, if the
motor hits something hard to move, the motor current can rise to
whatever the power supply can give to prevent the upcoming step loss if
it can. But the controller is now smarter, so if the error persists at
the next control cycle, indicating the motor will lose or has lost a
step, the controller turns the motor off to save itself and the motor.
and issues an alm closure to linuxcnc stopping it in its tracks thru the
e-stop toggle of the F2 function. Recovery is automatic because toggling
F2 removes all power from my machines, which is required to reset the
controllers to active duty.
3. This has been tested by purposely running the tool tip into a
stationary jaw on the Sheldon's 8" 4 jaw chuck at speeds above normal
cutting speeds. No damage to the chuck jaw, no damage to the maybe $20
carbide chip in the tool. The e-stop is that quick.
4. Just one problem. This has NEVER occurred during normal operation in
going on 3 years.
Actually 2 problems. They don't give away PSU's big enough to run 2 or 3
of these motors. The 1kw, 17 amp 60 volt supplies for the XY motors
aren't $30 models. Neither is the 1.5KW 90 volt 16A I will use with an
8.5NM motor on the Z.
5. This also discloses the other advantage of this newer tech, where
when I did this GO704 nearly a decade ago, 24 volts was king of the
steppers, limiting their speed and more importantly, the accels. This
will be considerably improve both speeds and accels because the new
controllers run at 90 volts (or more) happily. See the Hanpose site for
this new tech's best choices.
6. I expect the demand for bigger PSU's, driven by these new motors and
controllers will see 2kw PSU's at sub $50 price tags in about another
year. Maybe less. 60 and 72 volt PSU's are now commodity $35 to $40 items.
7. One other HUGE advantage: pull the PID's out of your .hal files, this
new tech does exactly what the trajectory planner asks them to do, no
more, no less. There are NO PID's where these motor/controllers have
gone here at the Heskett ranchette. PID's are rubber buffers we don't
need, leading to inter-axis errors we have little or no control over.
8. One other advantage over an AC powered igbt module. Speed of
response, where the igbt takes up to 1/120 second to respond to an
error, these new stepper/servo's do it in well under millisecond since
they run internally at ultrasonic speeds so we don't hear them. I have
no idea if these igbp modules can be operated at an AC input at 1
kilohertz which would equalize that, but first we'ed have to develop a
potential market for those inverters. That does not seem to be the case
at this time. If it happens, can we stand to listen to them?. I think
not. The stepper drivers we have run at ultrasonic speeds for a reason,
apparent silence. The shop dog can hear them though, bet on it the next
time you talk to him. :(>
As a CET, I think we've been pre-empted by the Chinese.
Just one warning, use the "42C" stuff in locations where they are told
to go AND STOP to operate, like a pawl stop in a lathe tool, or chain
driver in a tool changer. They use a hall effect device for position
feedback, which requires time expensive A/D conversions to develop the
equ of an optical quadrature encoder signal, so they move very
accurately but do it in jerks. They cannot be moved smoothly at any
speed above the speed of the internal A/D's. which on the present
offerings, several milliseconds per step. They would be great in an
emco5 tool changer clone.
They are also limited to about 30 volt supplies so available accels suffer.
Lesson is: optical encoders only for smooth motion. The higher
resolution of the encoder, the more accuracy potential there is.
For a discussion of this error, see a good text on Nuiquist error.
Actually, I am hoping to see an rvs30 worm drive clone with adjustable
backlash, so we could comp for wear-in. That would bring arc/second
accuracy to my A & B axis's. Say hello to Better gear hobbing than
Boston Gear.
I know this has been discussed before and it's time to get this idea going.
I'm tired of trying to source drives and vfds and having to learn how to
operate, integrate and maintain all these different devices, when they are
all functionally identical. (not to mention thay they are opaque and closed
source)
I'm starting out part of my investigation using a pine64 board. It's
risc-v based soc with 2 ethernet ports, wifi, bluetooth etc... I'm going to
initially interface it as an ethercat "device"
My first step is to get linux cnc running on it and go from there.
Does anyone have experience with anything risc-v related? Tips, advice,
resources pretty much any pointers are welcome to help me get up to speed
faster.
Also I need an initial igbt module "family" to target. Does anyone have any
suggesstions along those lines as well?
Hope all is well.
Thanks,
Curtis
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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
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