Stalling Steppers

[tauscnc]

Hey guys,

I need some help on my steppers. I have the K2 3925 router and the gantry is easy to move via the ballscres. So there is not a binding issue.

I had orginally tired my 180 oz steppers (2A) but they would stall out in the middle of fast movements. I played around but could not get them from stalling every now and then.

So I figured maybe I need larger steppers and got 640 oz ones form homeshopcnc. They are 2.3 volts 5.5 amp NEMA 34.

They also stall. So it has to be some issue with the compter, power supply, Mach 2 or 3.....etc.

POWER: 2 10 amp transformers one at 24V then series to 12V on the other...giving me a total of 36V and after the cap its at 52 volts. What is the total amps of transformers wired this way? 15 amps?

DRIVER: Gecko 201 with fan...cool as can be. No heating problem. I was using a 118K resistor which should of given me just shy of 5 amps (120 K is 5 amps). Is it better for me to run below the rated 5.5 amps or at 5.5 amps?
I am using Mach 3 and also have Mach 2.

COMPUTER: 900 Mhz coming out at 897 hz with stable 23776 plus in Mach 2 or Mach 3. Now I know art says it is to be 25000 but mine will not run there. I have NOTHING on the computer other then Mach 2/3 and what is needed to keep the computer running.

If I jog say 200 inches (lenght) and the MOTOR IS NOT CONNECTED TO THE MACHINE it will start spinning and keep going and then all of a sudden it will stall. Out of no where. It may jog 100 inches and then stall. I have tired to cut the speed in half and have had it still stall on me also. I don't know if the pluses coming from Mach are not stable, etc.

Is a servo setup that much better?

Any help would be so kindly taken

taus

[Jason Marsha]

What speed were you running the steppers at? if your steps per unit are set too high that may be problem as well.
At the highest RPM the stepper's torque rapidly decreases.
The 180 oz/inch steppers should work fine on a slick machine like yours unless the RPM is set too high coupled with the steppers not getting enough current. I have read somewhere that the steppers will pull a need more current than what is shown on their label if its a per phase rating .
I have the 127 oz/inch motors from Hobbycnc rated at 2 amps, with a 12 amp transformer and only had them stall when I had the machine running at 60" min. My JGRO obviously has a lot more binding pressures (backlash nut, slight misalignment of lead screw, no ballscrews) than your K2.

Jason

[ger21]

Typically, smaller steppers will spin faster than larger ones. So if you're trying to spin them too fast, that could be you're problem. Like Jason says, what rpm are you trying to spin them at?

I'd say there's a very good chance that the 180's just don't have enough torque. And you may be spinning the 640's fast enough where the torque has dropped way down. I checked the website and they don't show torque curves, so you really don't know how much torque you actually have at a given rpm. This is where servos have the advantage. Full torque (or close to it) at the full rpm range. And with servos, they are usually geared down to give you even more torque.

To take advantage of those 640 oz-in motors, you reallyneed to use screws with a higher lead, to keep the motor spinning slower where it has more torque. Something like 2 turns per inch. Unfortunately, that's probably a costly upgrade. But so are servos. But as I'm sure you've read, speed costs money.

One other thing. When running motors NOT connected to a machine, you may sometimes get resonance issues which cause lost steps. Sometimes they'll run better with a load on them.

[HuFlungDung]

The proper size of servo motors will not have a surprise stalling problem due to torque loss. But, the control system required is fancier. Perhaps Mach3 will accept encoder feedback now? That is what you would need to find out.

[jfong]

Assuming 1.8degree stepper motors, gecko set at 10microsteps. Your maximum pulse rate of 23776 will spin the motor about 713RPM. I've spun old style round type nema34's on my test bench over 2000rpm easily so I would think the more modern steppers can easily achieve 700+rpm, no load.

To get over 1000+ rpm reliably requires very smooth pulse train. I use a external frequency pulse generator to test max motor speed. Any small jitter in the pulse train at that speed can make the stepper stall easily. I find that turbocnc outputs very smooth pulse train so I sometimes use it to test motors high end speed. You might want to give that a try to see if you can narrow down the problem.

I have one PC setup with MACH2 and I couldn't get reliable stepper motor performance. Erratic behavior, stalling etc. I finally narrowed it down to the parallel port. The port had no problem printing to a test printer but just wouldn't work very good with MACH2/Turbocnc. I dug up a old ISA printer card and plugged it in. Problem disappeared.

Jim

[hulkonna]

I'm just a beginner , could any body tell me what is the most appropriate ranges of speed (rpm) to be used , with a small handmade machine

[ger21]

I saw on the Mach2/3 groups that Art says he thinks somethings interfereing with Mach. Keep us posted as to what you find out.

[Jason Marsha]

Hulkonna,
It all depends on what you are doing with the machine. I built the JGRO machine, free plans available for download, which I run at 40" /min (1016 mm/min) for cutting softer materials, harder stuff I experiment with first and may run at 20"/min (508 mm/min).
When I change my leadscrew I may increase my speeds.
If you machine is already finished post pictures and specs in the Woodworking Machines forum under the DIY section.

Jason

[tauscnc]

Hey guys,

I just checked the yahoo groups mach post I put there and will look into the pluse width and optimisation thing Art talks about.

Now the real questions is:

DO I JUST GO TO SERVO MOTORS ? I have a guy intersted in updating his system from the geckos I have and can sell those. The NEMA 34 I would also just put up for sale but the REAL question is

DO I JUST GO TO SERVO MOTORS....are they much better?

Also, if I read correctly below, :

HuFlungDung wrote Perhaps Mach3 will accept encoder feedback now? That is what you would need to find out.

So does Mach 2 or 3 not have that? If not how does the servo motor know it lost steps?

thanks guys
taus

[ger21]

So does Mach 2 or 3 not have that? If not how does the servo motor know it lost steps?

thanks guys
taus

If you're using Gecko or Rutex servo drives, the encoders connect to the drives. The drives keep track of where the servo is, if it gets out of position, the drive will fault. Mach2/3 doesn't know the difference if you use servos or steppers, it just sends steps and direction info to the drives.

There is an add-on board for Mach3 that uses encoders and keeps track of where you're machine is. If it gets out of position, the machine will pause, allowing you to continue on after diagnosing any problems. http://www.rogersmachine.net/encoderinterface.html

I don't believe Mach3 will ever be able to run closed loop using encoder info, the parallel port just isn't fast enough. Mach4 will probably have this ability in the future, though, but it will use the Gecko G100 (G-Rex) to handle it.

[tauscnc]

So when the driver faults the motor does it just stop the motors? If so haven't you really lost a step or two already which would mean your part is not going to be right anyway. How does someone restart the system, make up for the loss of steps, and keep going? In the stepper system if it misses steps it just keeps going..later, depending on the work you figure this out.

So then the servo motors really aren't much better then my steppers in this situation.
Is that right?

thanks
taus

[AbSat]

Quote"
POWER: 2 10 amp transformers one at 24V then series to 12V on the other...giving me a total of 36V and after the cap its at 52 volts. What is the total amps of transformers wired this way? 15 amps? " end quote.

The total amps will never be more than the transformer with the lowest amps.
So when both transformers are 10 amp types the max current will be 10 amps.

AbSat.