CNC software highest step rate

Hi,
What's the highest step frequency one can expect from popular CNC software these days? 100kHz? 200kHz?

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What do you mean by step rate? Instructions/sec?
snipped-for-privacy@hotmail.com wrote:

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How about inches / sec Martin Eastburn @ home at Lions' Lair with our computer lionslair at consolidated dot net NRA LOH, NRA Life NRA Second Amendment Task Force Charter Founder
Tim Killian wrote:

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Mach3 will go as high as 45 kHz, although I can't imagine why. Mechanical resonance limits practical speeds to below 25 kHz.
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That's low IMO, you mean there isn't anything out there approaching 100kHz?

Typically, the same software is used by step compatible servo drives. Example, a 4X only servo drive (Gecko 320 for example) driving a 2600 RPM DC motor with a 500 CPR encoder mounted on the motor shaft needs a step rate of 88kHz in order for the motor to reach maximum speed. Resonance is a non-issue.
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To clarify, I am not aware of faster speeds. Available step rate is so not the limiting factor on my setup. Unless you're talking about something else entirely, of course.

Sure, if you can get 2600 rpm into your system. Mechanical resonance overwhelms steppers at about 1600 rpm. What are you looking at that it becomes a "non-issue"? I had heard, I think, about the 320's adaptive micro-stepping. If it's that effective, I might give it a shot. 300 ipm seems plenty, but faster is always gooderer.
As for step rate on a PC, EMC runs on RTLinux. Dunno why it thinks it needs realtime to run a few simple steppers, but maybe worth looking at for your application.
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[If you really want a higher step pulse rate, you could get a G-101 "G-rex" board from Geckodrive. They claim to put out over 4 million step pulses per second: http://www.geckodrive.com/manuals/G101%20Features.pdf ]

[It's a non-issue because it's driving a servo motor; they don't have the same resonance problems as steppers. While the control can send the same step/direction signals that control steppers, the 320 drives will accept those and convert them to something servos can run with. 2600 rpm motors usually require some belt reduction to be useful in a CNC system, though. ]

[Realtime is necessary to avoid having your milling job disrupted when the OS decides to reshuffle its memory, or do other "housekeeping" functions. Mach2 gets around this by infecting Windows like a virus, to grab first priority for step pulsing. Most other Windows-based systems, like Flashcut's, use a dedicated pulse generator of some sort, instead of forcing the computer to do it.]
Andrew Werby www.computersculpture.com

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    [ ... ]

    Apparently -- a *non*-stepper fed from something which thinks that it is driving a stepper. Feed the steps that fast and the servo will be moving smoothly, instead of jumping and stopping to excite resonances.

    EMC runs on a real-time kernel because it can *also* talk to analog servo motors, with encoders giving feedback as to the actual position, which I think is more interrupt intensive than driving a stepper. You've got three axes all reporting change of position at the same time (sometimes), and updates to the D/A converters to reset the servo speed to compensate for load or whatever, and possible interrupts from the limit switches as well. You want to give those limit switches very high priority so it can stop things before you hit a hard stop and damage the ballscrews and nuts or something else.
    Enjoy,         DoN.
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I'd been curious about that. Why are the limit switches not typically hardwired to disable the drive, but rather simply reports impending crisis to the software? It seems something already has gone wrong by that time.
So, EMC can run closed loop directly without additional hardware support? (Beyond power drivers for the stepper, that is. ?) That's something, given that old PC's are essentially freebies. It would seem a perfect waste of computational resources otherwise. Replacing Gecko 320's, for example, with simple drivers would be a pretty big savings for the hobbyist.
In general, are servos considerably different from a stepper with an encoder?
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Let's make certain we're on the same page first.....The Gecko 320 is a DC servo drive. Besides cost, its 4X only support is another limitation for the hobbyist who is likely to be looking at surplus DC motors. I bought one for evaluation and concluded it was not the drive for me. Instead, I went with simple microcontroller based drives with both 1X and 4X support at about half the price. So if we 're talking about the same Gecko drive then simpler and cheaper drives already exist.
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Greetings Oparr, What do you mean by only 4X support. What are 1X and 4X? And why would 4X only be a problem with surplus motors? I have bought 3 of these drivers and the specs seem to me like they will work with the servo motors & encoders I already have and the step and direction software I have. Eric
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Typically, the incremental quadrature encoder has A and B channels with pulses 90 degrees out of phase when rotating. Not only does this allow for the decoding of direction information but also allows for a pulse rate four times that of either channel. Hence the 4X.
If a servo drive only supports 4X then the step frequency required from software to support any encoder RPM is;
(RPM/60)*CPR*4
If the encoder is mounted on the motor shaft as opposed to a driven shaft geared down from the motor shaft then you have a worst case scenario in terms of required software step rate. If the highest step rate from software is less than the above when RPM is the maximum RPM of the motor then the motor will never be able to reach top speed.
1X support will reduce the above requirement by a factor of four.
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Oparr, I forgot to ask what the cheaper drives are that you have found. I will be building a positioning table for plasma cutting this winter if time permits. Less expensive drives would be nice. Eric

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>I forgot to ask what the cheaper drives are that you have found.
Follow the link below. Note the voltage and current limitations when compared to the Gecko 320, they may not meet your requirements;
http://www.cadcamcadcam.com/index.asp?PageAction=VIEWPROD&ProdID 
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oparr writes:

30 volts at 5 amps? Hopelessly underrated for most CNC applications.
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Correct! Hobbyist applications are only a small fraction of all CNC applications.
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I don't know of *any* metalworking machines that will scoot with such tiny amounts power, unless you're gearing down to nothing. Maybe you're suggesting PCB drills or wood routers that don't require much torque.
150 watts for $80, vs Gecko's 1600 watts for $120, I'd choose the latter. The former is no bargain, per watt.
It *is* all about the oomph, you know. Why would a hobbyist hand-build a car, and then put a lawnmower engine in it?
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Both scoot and tiny are relatives. Whatever, there's woodworking, robotics and several other fields where lower torque levels are commonplace.

Its more like $195.00 vs $360.00 if you're catering to 3 axes.

No, I don't know. How old are you? You seem like a impressionable teenager who drives a car with one of those 6" tail pipes that's good for nothing but noise.
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Thanks Oparr for both replies. Eric
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Like Eric, I don't know what 4X and 1X are. Is that 4 microsteps vs. full step? Something else?
Let's back all the way up. The original context was about EMC and its ability to drive servos on the PC's parallel port. That's where the 320 came in. Most PC software operate steppers in open-loop only: no encoder input, and sends step and direction lines going out. The 320 reads the encoder quadrature input, closing the loop. The encoder resolution has to match the step size. That is, one encoder tick for each step or microstep. When they get too far out of sync, the 320 signals a fault and then resets. The original quote refers to replacing the 320's functionality with a freebie, otherwise unused old PC running EMC, to run steppers in closed loop.
I know nothing about servos. Simplistically, I think of them as steppers with a matched encoder. Probably too simplistic, but workable, since I don't expect to ever want to pay the extra for whatever they bring.
I'm aware of other and cheaper drives, ranging from HobbyCNC's u-solder-it 4-axis $99 special, and up.
I'm not sure what it was you were trying to say.
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