HOORAH! I won!

I never 'win' anything, but today on CNCZone I WON a give-away contest from Gecko Drives! (4 of about 200+ entries).
They have a new stepper driver that will AUTOTUNE to any given attached stepper/load in order to (according to them) totally eliminate resonance at all frequencies. (by _selective_ micro-micro stepping in those zones where resonance is an issue)
If it works as they say, it'll be by 'go-to' driver for all future stepper projects. It's not cheap, but if it does as it's spec'd, it'll be worth every penny.
The new G241 drive.
LLoyd
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On 2016-08-20, Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

Awesome!!!
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On Saturday, August 20, 2016 at 2:02:29 PM UTC-4, Ignoramus24768 wrote:

What do you mean "awesome"? I thought he was talking about something real, like the Lottery (not un-claimed freight).
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snipped-for-privacy@hotmail.com fired this volley in

If he means what I do, it's 'real like the Lottery' for guys who design stepper-based machinery.
Lloyd
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On Sat, 20 Aug 2016 12:55:08 -0500, "Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote: >I never 'win' anything, but today on CNCZone I WON a give-away contest from

Congrats, Lloyd. Not a bad prize! I hope it works as stated.
--
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Please keep us posted. I used to be a big fan of GeckoDrives, but currently I only have one installed (G540 (4-G201s as part of an assembley)) and its probably been a year since the last time I used it. I would suggest keeping it at about 60% of rated voltage and currrent. It might last longer. My experience has been when you push G201s or G320Xs to near their ratings they don't last all that long. Haven't used any other GeckoDrives myself, but I've been thru a few of those.
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

Congratulations. How does the controller detect resonance?
I ask because I tried to write an assembly-language pulse coding routine that critically damped the stepping of a print head on a long cable drive without positional feedback to the computer, though I could see the head movement on an oscilloscope with an optical sensor. http://hyperphysics.phy-astr.gsu.edu/hbase/oscda2.html
All I "won" last week was two used garage door openers. They might be precise enough to paint lines in a parking lot, or position logs on my sawmill.
--jsw
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Jim, I don't know, but I'm ready to learn.
On one of my customers' machines, I have a 4-chemical feeder/screener/weigher device that simply CANNOT be used in a fairly wide range of speeds that are all within the steppers' and drives' capabilities, because of the low force but really high inertia of the screening drums.
I 'programmed around it' in software, but I'd really like to gain back those intermediate speeds I lost.
LLoyd
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E. Sponenburgh wrote:

Slow the control loop down. It's trying too hard given the inertia of the screening drum.
I'm assuming that the screening drum cannot be designed to have sufficiently lower inertia, and that it's OK for the drum to take time to get up to speed, and to react sluggishly to changes.
Joe Gwinn
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Lloyd - is that a continuous weigher or a stop & go type?
Hul
Lloyd E. Sponenburgh <lloydspinsidemindspring.com> wrote:

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Stop and go. And contrary to advice, it's already accelerating/decelerating the drums as slowly as necessary to avoid inertia-induced resonances at all speeds, except in a 'band' in the middle speeds. I can even 'jump' from the either end outside of the band to the other 'smooth' speed area in one step, and it will run smoothly both below and above... just not IN the band, no matter how slowly it's approached (from either side).
It's presently running on Gecko 201s, and Gecko themselves feel that the new 241 will fix the problem. I sure hope so!
LLoyd
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"Lloyd E. Sponenburgh" <lloydspinsidemindspring.com> wrote in message

The drives may not be the problem. https://en.wikipedia.org/wiki/Critical_speed http://www.engineersedge.com/bearing/critical-speed-distributed-load.htm
I can see the transition between rotating around the geometric center below the critical speed and around the center of gravity above it in the spin cycle of my washing machine, and on a paint stirrer in a variable speed drill. At the critical speed where vibration amplitude is theoretically infinite the agitator lurches sideways and the stirrer shaft bows out. Above it both settle down and spin smoothly again.
--jsw
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This was my next thought as well.
The drum may need to be made far stiffer.
Joe Gwinn
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It couldn't possibly made 'stiffer'. It's heavy material anchored securely at both ends with large bearings. There's no 'wobble' in this device. If you spin the drum to 3600 rpm, you can't even feel the imbalance.
That's not it. You'd have to know all the 'dynamics' in the system to fully understand, and by both contract and limited time, I can't describe it in enough detail to do that.
Lloyd
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E. Sponenburgh wrote:

Well, to be precise, if critical speed is the issue, the resonant frequency in bending needs to be raised. This is a combination of mass (lower is better) and stiffness (higher is better).

Well, if we cannot get the details, the magic suggestion may be a long time coming. Critical details are slowly emerging.
I would do the computation for critical speed, and see if it lands anywhere in the normal speed range.
Joe Gwinn
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There is a thread that may be of interest: "Re: compensating phase shift" in newsgroup sci.electronics.design during August 2016. Lots on how to handle resonances in servo loops.
Joe Gwinn
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Thanks, Joe. That might be useful.
And, THAT I can accept. The idea proffered that the assembly is flexing was so far afield I gave up on the ideas here.
LLoyd
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E. Sponenburgh wrote:

Welcome, Lloyd. Also look at the parallel thread with a similar name.

Umm. Don't be so quick - the vibration may not need to be visible to mess with the servo.
Joe
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Joe... I'm not 'discounting' it. I've _eliminated_ it. The structure of that rotor is such that it would take about two-hundred-thirty pounds of force directly at its middle to flex the assembly 1/4-thou.
It has 7oz of force on its middle, and is turning below 20 rpm, tops.
Lloyd
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E. Sponenburgh wrote:

Ahh. Useful details. What does it weigh, and how stiff are the bearings? One can get critical speed issues with springy bearings as well. Although 20 rpm would seem to be safe, regardless, unless the drum is very heavy.
I guess I don't fully visualize the setup.
Joe Gwinn
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