Messages

991

General Mach Discussion / Re: Really need help

« on: August 16, 2009, 08:10:40 AM »

I'm, sorry, but I don't know what you mean... "double iso"  (duh)

You should protect your PC from a short that could send motor voltage to fry the PC port or worse.  Since your drives are already isolated, you do not need additional isolation between them and the PC. For example, Gecko drives are isolated, so the BOB I linked you to comes in a less expensive 'Gecko version', that has no isolation on the pins typically used to connect the drives.

My money is on your RF gizmo being the prime suspect, so since you do not need isolation for the drives and you have a no-frills BOB to try our, my vote is to go for it. Worth a try.

Full step vs half step vs micro-step *should* have no bearing of whether the setup functions correctly or not, although there are reports that checking off the 'sherline half step mode' box in Mach does solve certain mysterious lost step problems . . . .  primarily on the Z axis for some reason . . . .even though it shouldn't have any effect.

Mostly I am interested in how the little scope works for you. When I had the Gecko servo drive, I was sniffing around available scopes to use in tuning and I selected this one: http://www.saelig.com/PSPCEL/PSPC019.htm but never bought it as I got rid of the Gecko instaed.

992

General Mach Discussion / Re: Really need help

« on: August 16, 2009, 07:44:55 AM »

YOU are right IF I just wanted to drive around town showing off I would buy the sports car those speeds shure are impressive.

BUT IF I wanted to actually do some work and actually MOVE the dirt I would BUY the dumptruck every time.

Exactly. This is why the whole stepper vs servo argument is meaningless if undertaken out of context.

Certainly the debate is valid in applications where there is overlap . . . dump truck and Firarri will both take you and a friend to the local Blockbuster Video Store to rent a movie. Speed is identical while sitting in a traffic jam . .  etc. i.e. applications wherein the advatages of either are not required nor are the disadvantages of either going to hinder the machine's function.

But as you correctly point out, the objective, winning a race or hauling dirt,  should be the first item of discussion before any recommendations start being passing around. Unfortunately, more often that not, the fur starts flying before anyone knows what the application is. This was pretty confusing to me when I first entered the fray.


Incidentally, is 'VMAX' related to the motorcycle?

993

General Mach Discussion / Re: cnc driver board

« on: August 16, 2009, 07:05:21 AM »

The voltage is 3.6 v. and 4 phase 3.0A. they have 6 wires.

In that case, you will be running them at 3.0A which is OK for the Gecko mentioned. If you go that way, I would suggest you get a 48V power supply.

My advise, however would be to run the steppers at 72V with Gecko 203Vs.   It's more money, but you will be a lot happier with the performance, especially if you rout wood and need the machine to move relatively quickly. Stepper power drops off scary quick as the speed comes up and the extra juice really helps them keep on truckin' so that you can keep the feed rate out of the 'burn the workpiece' range and hopefully never be plagued by lost steps and ruined parts.

Good luck with your project!

994

General Mach Discussion / Re: Really need help

« on: August 15, 2009, 09:57:27 AM »

I believe what VMAX  refers to, is the proper selection of a component  . . . .

That is my question. How does one go about selecting, identifing, determining a 'well engineered' component. A statment was made, I'm just asking it be expanded to a useful point. Exactly how does one go about matching these components together as you correctly point out must be accomplished. I see a recurring contradiction whereing stepper systems are consistently touted as being 'easy', 'uncomplicated', etc, yet there is a never ending stream of posts with 'missing steps' or something similar as part of the subject line and then a pile of shot-in-the-dark suggestions on how to diagnose the problem. Not unlike this very thread.

Therefor, the logical conclusion is that this is not so simple as it's made out to be.

It's a serious question. I've done a ton of research on these topics and I don't reacall finding any clear advice on exactly how to select a 'quality' component from the vast choices available in the world of steppers. i.e. is it all down to getign a consensus or recommendation from existing users, or is there some way to be proactive in interpreting a spec, graph, or other perfomance documentation?

I.e., starting with a clean sheet of paper, what are the caveats to avoid and what is a logical path to sucess in setting up a stepper system. I'm asking for the benefit of the OP and others, as I am not planning to use steppers again.

995

General Mach Discussion / Re: Really need help

« on: August 15, 2009, 09:39:54 AM »

I believe Mariss from Gecko is the designer of the Centent drives. It would be interesting to hear what he thinks about your findings, as I was under the impression that Geckos are far more advanced than the Centent.

Are Mariss and Marcus the same person?  I had email exchanges with Marcuss Freimanis (may have spelled that wrong), but I ocationally see 'Mariss' mentioned.

If the Gecko is far more advanced, it would be quite a bargain at half the price of the Centent. I found no discrenable difference between the two drives with small (NEMA23 400oz-in) motors.

996

Show"N"Tell ( Your Machines) / Re: Success! Mini Machining Center under Mach3 control - Video link

« on: August 15, 2009, 09:26:24 AM »

Project re-opened  . . . .  two new wrinkles for those following along;

I have avoided testing the 4th axis with a heavy lathe chuck holding a heavy workpiece because of concern over BEMF smoking the Rutex drive during a fast decel from 3,000RPM motor speed.

Two possible solutions have surfaced:

1) I have figured out how to change the axis accelerating parameters with a macro. This will be much better than trying to program a velocity step down in G-code (my previous solution). I'll be experimenting with that in coming weeks.

2) A new servo drive from CNCdrives that has an automatic brake resistor feature that monitors voltage and dumps excess automatically to a power resistor. This is nothing new, but it is new at a $170 price point. This new drive was shipped to me yesterday along with the same company's mid range drive. Anyone interested can watch the review as these drives are next up.

997

General Mach Discussion / Re: Has anyone used Granite devices VSD-E sevro drives?

« on: August 15, 2009, 08:54:11 AM »

I may not be reviewing the Granite drive. It has very impressive specs and many kudos, but it is also very expensive and that extra cost goes to features that I would not use in my application. The Granite drive was the only offering I knew of that would meet all of my requirements, and I was about to buy one when I found what may be a suitable alternative.

Thanks to Hood's nagging, I spent (read - suffered thru) more time researching on the Yahoo group and the fellow who seems to be the head Guru there mentioned CNCdrives. I looked into that and discovered two new products (that are not on their web site), and if they perform to spec, these will be the solution I have been looking for and at least $100 less than the Granite drive.

I've purchase both their mid range Whale3 drive and their high end Dugong drive, both of which shipped to me yesterday.

The Dugong has two of the most attractive features of the Granite; namely and built in automatic brake resistor circuit and the ability to flash firmware updates. The reputation of both Rutex and Viper to burn out seems to be caused by BEMF. The Dugong drive will eliminate this possibility . . . . again, IF it performs as advertised.

We shall see. I will be reviewing these drives next.

998

General Mach Discussion / Re: Has anyone used DMM technology AC servo drive or motors?

« on: August 15, 2009, 08:34:05 AM »

OK, pulling the plug on this product. A little too far out of the mainstream, no interest, and a close read of the docs show a small fixed following error.

Next drives to be reviewed will be CNCdrives models Whale3 and Dugong.  Both were shipped to me yesterday.

999

General Mach Discussion / Re: cnc driver board

« on: August 15, 2009, 08:26:41 AM »

Gecko also sells the same drives individually as the G251, but you would then also need one of Peter's excellent Break Out Boards.

I don;t know if the 540 has any relays in it, but you would want to consider that to switch the spindle on and off. Peter's BOB had relays on it and you use those to swithc inexpensive AC relays to turn the spindle on and off.

What is the voltage spec on your motors? 4 wire or 8 wire?

There are different ways to wire up bipolar steppers. Make sure the low end Geckos have enough capacity for what you want to do.

The power can be switching type or unregulated for steppers, but remember that steppers should run many, many times their rated voltage. Read some of the excellent info on the Gecko site for sizing power supplies.

I first ran my 4V steppers at 36V and it was pretty lame and stalled easily. I switched to 72V and it was literally as if I had replaced the steppers with twice as powereful motors. No more stalling.

1000

General Mach Discussion / Re: Really need help

« on: August 15, 2009, 08:05:35 AM »

I just skimmed through this, and it doesn't appear that anyone mentioned that resonance may be the culprit? Steppers are notorious for mid band resonance, especially when running in full steps. Does your drive have microstep settings, and have you tried them?

If not, a damper may help. It's helped a lot of people at CNC Zone double their speed and make their machines far more reliable.
http://www.cnczone.com/forums/showthread.php?p=256639#post256639

I've just discovered something to throw into this arena. I replaced a Gecko 203V with a used Centent 143 'anti resonance' stepper drive. This is an expensive commercial drive about three times the size of the Gecko, but available used for $45 to $100. There is also a 142 and a 146 model with sightly different specs.

Let me say that I love the Gecko203V for it's 'unkillableness' which saved my bacon more than once, and it does an excellent job with small(ish) steppers. But performance wise, the Centent drive is in a whole differnet category. There is NO resonance at ANY speed running a 900 oz-in NEMA 34 stepper parallel at 22x voltage. Although it never lost steps, this was my 'problem child' stepper on the Z axis from the standpoint of resonance. I've heard it said more that a few times that the commercial drives (stepper and servo) are in a different class altogether and that is certainly the case with this product.