Slaving Z & A but can't get speed

[plasticbaldy]

I can't get adequate speed. My CNC router ran well when driven by chain but my home made machine does lots of work & kept wearing out sprockets & pulleys so I upgraded to ballscrews.

I'm running G201s & upgraded from one motor driving sprockets & chain down each side with a common shaft across the table to 2 ballscrews with A slaved to X on Mach3.

My 2 stepper motors on the ballscrews have much more torque than the single one I had driving the chain so I can't see that the problem is due to insufficient torque. My power supply is definitely adequate.

I've even tried while the drive couplings are disconnected & it sounds like one motor (sometimes X - sometimes A) misses steps & sometimes stalls with no load or with a tiny bit of hand friction.

I don't understand why I can rotate the stepper motor by hand and the holding torque seems no different when the driver is on or off. There is not much holding torque. I can just feel the notchiness of the magnets. The holding torque feels the same when the steppers are powered or not.

When I ran the carriage by chain I got 2500mm/min easily with a 200 oz/in motor. Now I have 2 matched motors, each about 1400 oz/in & all I can get is 1200mm/min before one motor stalls/stops/misses steps/whatever. I can't tell which (stall/stops/misses steps/whatever) but when it happens one side of the carriage stops. It's not always the same side which stops. It's not always the same direction when it stops. It's not always the same location where it stops.

I'm confident that the problem isn't carriage drag or a mechanical design fault/problem of the ballscrew installation. The ballscrew installation is drag free.

I've tried different stepper motors (identical pairs) on X & A and the problem is the same so I don't believe I have faulty motors.

Ideas and suggestions would be greatly appreciated please.

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[plasticbaldy]

Woops. Title should have been 'Slaving X & A but can't get speed'.
(and no, I don't want cocaine instead. lol)

[ger21]

I don't understand why I can rotate the stepper motor by hand and the holding torque seems no different when the driver is on or off.

Sounds like something is wired wrong. There should be a big difference.

Do you have the correct current resistors? What are the motors current and inductance ratings, and what voltage are you running at?

Keep in mind that larger motors have a much lower top speed than smaller ones. Add the fact that ballscrews will probably require much higher rpm from the steppers to get an equivalent speed to the chain, and you might not get a whole lot more speed than you had withthe chain drive. What is the pitch of the screws?

[plasticbaldy]

Thanks Gerry. I had resistors in the drivers that limited current to 5A & I think it was the same but I'll reinstall them & check. By the same I mean that the steppers had little resistance with the driver on. BTW the steppers get to about 45C temperature which indicates that the coils are functioning - no ?
5mm pitch screw.
We connected a large series battery power supply & the motors draw 3.5A. I have 2 power supplies split. 60V 7A on X & A Drviers & 40 A on Y & Z.
Don't know the inductance.
The problem isn't the max speed of the steppers because it runs fast enough unloaded for a short while before one motor skips/stalls/stops.

[plasticbaldy]

Sounds like something is wired wrong. There should be a big difference.

Do you have the correct current resistors? What are the motors current and inductance ratings, and what voltage are you running at?

Keep in mind that larger motors have a much lower top speed than smaller ones. Add the fact that ballscrews will probably require much higher rpm from the steppers to get an equivalent speed to the chain, and you might not get a whole lot more speed than you had withthe chain drive. What is the pitch of the screws?

OK in retrospect there is a big difference in holding torque with the driver on. I was comparing the holding torque after switching the driver off but there was still power in the capacitors (or whatever). After a while the power drops away & there is no holding torque.

I've decided that my problem isn't speed as such. When I set more speed on Mach3 Motor Tuning the torque isn't sufficient. I can stall my steppers with hand friction way too easily. A friend with a machine that has much smaller steppers says his torque is much greater than mine. I've tried 480oz/in motors as well as 1400+oz/in motors & the torque isn't much different. whether I have resistors set for 5A or remove them for unlimited current the torque doesn't change. I have a 60V 7A power supply.

I don't really understand half step/quarter step etc but a suggestion has been to change to half or quarter but I don't have any idea how. I'm using G201 10uSTEP drives & will attach a picture of my breakout board.

[plasticbaldy]

I'm looking for a wiring fault.
Regarding DC Ground (-ve) at the Geckos. I've noticed that the way the power supplies are wired, my DC Ground (-ve) at the Geckos is not common with the -ve from the 5V power supply to the Breakout Board. Should I bridge these ?

[plasticbaldy]

Next question ; My CNC router is driven by 2 of these NEMA34 8 wire stepper motors wired parallel approx 152mm (6") long driving ballscrews on X & A (A Slaved to X). Even though they're quite big the motors draw less than 2.5A at 60V when I don't limit the current. ? (Or am I understanding this wrong ?)
I've searched the net but can't get the motor specs. The only identifying marking is the phone number of the Chinese Manufacturer - Yima, who doesn't reply & only has a Chinese language website.
Is there something I can measure with a volt/ammeter that will give me some idea of what torque to expect from these.
Maybe the motors are an old design that's gutless ?
Before I spend money on replacement motors, is there a way to power them up with DC or AC power to gauge the real torque (by feeling & comparing a pulley stall force by hand) without using my Gecko driver & in this way determine if my problem is really the motors lack of torque or if my problem is driver wiring/power supply/other electronic wiring fault ?

[ger21]

Do you have any information on the motors I can see?

Not sure about the grounds, but with Gecko's, you're locked into 10 microsteps. no half or quarter steps.

[plasticbaldy]

There's no plate on the motors.
I've searched the net but can't get the motor specs. The only identifying marking is the phone number of the Chinese Manufacturer - Yima, who doesn't reply & only has a Chinese language website.

[plasticbaldy]

Can I somehow drive this motor with a 28V 60A ESC as used for RC model aeroplanes to get a feel foir its torque when not driven my my Gecko ? If so then how would I wire it ?
Alternatively can I just power up one coil from a power supply & get a feel for it's holding torque ?

[plasticbaldy]

I'm back to this project. Still having motor stall problems.

I've discovered that when the NEMA 34 800+ oz/in motor(s) are running at more than about 400 RPM they start to make an irregular bumping/clunking sound and will eventually stall. Yet while they are running at this speed (before they stall themselves) I can't stall them by applying resistance to the carriage. No amount of pushing against the carriage will stall the motors. This equates to only 2000mm/min carriage speed with my 5mm pitch leadscrew.

It seems to me that approx 400 RPM is as much as my motors can handle without skipping/stalling & it's not a load problem and not due to lack of torque but some inherent motor design limitation.

I fitted some shorter NEMA34 motors - approx 500 oz/in and I get the same experience but at about 500 RPM. So it will run faster !

Yet there's no mention of RPM limitation in Stepper Motor specification.
Am I Robinson Crusoe ?

Why isn't this part of the discussion in setting up the mechanical components of drives.

Maybe if I step up the drive rpm to 3 or 4 times motor speed with a tooth belt my problems will go away.

[ger21]

Sounds like resonance. Have you adjusted the trimpot on the drives?

[plasticbaldy]

Sounds like resonance. Have you adjusted the trimpot on the drives?

Can you please give me some more information Gerry. Gecko G201 Drives. Trimpot ? Where ? How ?

[plasticbaldy]

Sounds like resonance. Have you adjusted the trimpot on the drives?

Should I replace the G201s with better/different drives ? How do I determine if resonance is the problem ?

[ger21]

Should be a small pot where it says "adjust". There's a small paragraph in the manual that explains how to adjust it.
Support

[plasticbaldy]

Please tell me what resonance is in laymans terms.

[plasticbaldy]

I installed a 20A @60V power supply (previous one was 7A @60V). Also installed timing belt drives to step up the ballscrew speed by about 60% and got about a 20% improvement in top speed before one or other slaved motors stalls. Went through the trim pot adjustment procedure to cure possible resonance but trim pots were set correctly.
Any other ideas please ?

[plasticbaldy]

Maybe 7A max from the Gekkos isn't sufficient for these big steppers ?

[ger21]

Without knowing the specs of the steppers, it's hard to say. But my guess is that's very unlikely.

Most of the larger Chinese steppers people are buying are very high inductance, low current motors.
Stepper motors lose torque as rpm increases. The higher the inductance, the faster the torque drops off. In order to get more speed, you need to supply higher voltages. Usable rpm is proportional to voltage.
The problem with these motors, is that the inductance is so high that they require very high voltages to get high speeds, usually 120V or more. Since Geckos can only use an 80V supply, you'll never see maximum performance from them.

Also, with larger motors, the torque falls off much faster than smaller motors. Generally, as holding torque goes up, max rpm goes down.

Since you ran the machine before with 200 oz steppers, I'm assuming it's not a big, heavy machine.
My guess is that if you tried some high current, low inductance motors, you'd get much better performance.
I'd try something in the 450oz range with a current rating of around 6 amps.

[plasticbaldy]

Thanks Gerry. Although I did rebuild the carriage stiffer & 50% heavier since replacing the single, chain driven system that worked faster with the much smaller 200oz stepper. These 2 steppers are monsters by comparison. And these same motors can run really fast on Y & Z axis at only 5A.
With 2 driving the X the load wouldn't be much more on each than the single one on Y. There's some black magic going on here.

There definitely isn't a binding problem anywhere on X. If I disconnect the drives I can push the carriage up & down the machine by pushing on one or the other side only & even change direction quickly without causing a bind.

I've tried much slower and faster accelleration without improvement.

Is there any way of discovering the specs of my motors ? The only information on the