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Author Topic: Stepper motors that shudder.  (Read 534 times)

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Stepper motors that shudder.
« on: April 01, 2019, 02:25:55 AM »
I have a router, running it with Nema 23 425lb motors on screws. The Y axis has double motors. If I set the speeds any higher than 1800, whilst jogging my Nema 23s will stop, with a corresponding brrrrr sound. Kind of like the sound my Milwaukee driver makes pushing in a screw.

The jog speed with a 5mm pitch screw is about 1800, anything above that I will have the above fault appear. But am unsure if I am asking too much of these motors or do I need to troubleshoot them? If I slow everything down it all becomes good and happy.

Or, is it just I should upgrade to Nema 34 motors?

Also I see my drivers are up to 50V and I am supplying them with 36V. Is it better for the drivers to be receiving the higher voltage?

What do you think?

Offline reuelt

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Re: Stepper motors that shudder.
« Reply #1 on: April 01, 2019, 03:26:23 AM »
Please increase your Mach3 kennel speed from 25000Hz to 36000Hz or even 45000Hz if that is possible.
(MACH3 Demo version users are limited to 25000Hz)
"the gift of God is eternal life through Jesus Christ our Lord"
Re: Stepper motors that shudder.
« Reply #2 on: April 01, 2019, 03:43:51 AM »
Really? Cool ok will do. Have a license. Thanks

Offline RICH

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Re: Stepper motors that shudder.
« Reply #3 on: April 01, 2019, 06:20:23 AM »
Suggest you go to the Gecko site and read the information on stepper motors. In particular Step Motor Basics.

RICH
 

Offline ger21

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Re: Stepper motors that shudder.
« Reply #4 on: April 01, 2019, 07:03:44 AM »
Most 425oz Nema 23 motors really need close to 100V to get the best performance out of them. They just can't spin very fast with 36V. And the 5mm pitch screws require high rpm to get any speed.
You need the lowest inductance motors you can find, preferably around 2mH or less. And run the highest voltage you can.
Gerry

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Re: Stepper motors that shudder.
« Reply #5 on: April 02, 2019, 02:36:26 PM »
Gerry is that a fact? I have been using the same machine, with the same setup from day one. Its been running fantastically for over 5 years until I put voltage where voltage should not go.... But I have been running the motors slow, quite slow in fact.

So am replacing my $10 BOB along with the DQ543ma drivers. I will try out the improved Chinese BOB board, and purchase 2 of them they are so cheap.

If I am to look at running 100V, with the fact I dont have any money to purchase anything but Chinese what are the recommended stepper drivers out there that people have had successes with? The MB450A looks the same but is still a 50V input. I wonder if I need to revisit my setup.

Offline ger21

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Re: Stepper motors that shudder.
« Reply #6 on: April 02, 2019, 03:17:55 PM »
You won't find any drives that can handle 100V DC. I've seen a lot of people run those motors at 72V, with an 80V drive.

Another option are some Leadshine drives that run on AC, and don't need a DC power supply. I believe that they actually supply over 100VDC, but they're not cheap.


Are you saying it used to work fine, then something changed? How fast was it running before?

How fast do you want it to go?
Gerry

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Re: Stepper motors that shudder.
« Reply #7 on: April 02, 2019, 03:48:39 PM »
I have been using a machine that jogs on 900mm. After blowing up my PC, and plugging in an old Mach 3 I have installed on another PC I noticed the motors jogging at 1200mm which would have been day one commission. I have been decreasing that speed as the machine has gotten older. And I kind of liked the faster speed.

So on Monday I tuned my motors up to 2000mm, all the axis's will run on that speed except for the heavier Y gantry which will run for a period only to slip or brrrr out. What is the term for that? Its like a stall.

Looking further, with a 5mm pitch it appears I am asking the steppers to run at 400rpm and that seems to be the limit with the torque dropping right off yes? If I was able to run the steppers at 1800mm or 360rpm is that a reasonable request of a Nema 23?

I will say, the lower speeds have served me very well over the years. Its just a long time to jog the length of the table lol
Re: Stepper motors that shudder.
« Reply #8 on: April 02, 2019, 06:43:04 PM »
Hi,

Quote
What is the term for that? Its like a stall

Just 'stall' or 'losing steps'.

Quote
Looking further, with a 5mm pitch it appears I am asking the steppers to run at 400rpm and that seems to be the limit with the torque dropping right off yes?

All stepper motors, irrespective of design drop torque as the speed increases. The principle determinant in how quickly the torque
degrades is the inductance of the motor. The most common specification of a stepper is its holding torque, in your case
425 oz.in. Inexperienced buyers tend to focus of holding torque. Savvy buyers on the other hand look for the inductance
of a motor, the lower the inductance the better because the motor will run faster with less torque degradation.

It may well be that if you bought steppers of the same size (23) and holding torque (425oz.in) but low (less than 2mH)
inductance would handily outperform the steppers you have. It may be also that if you bought lower torque motors,
say 300 oz.in but had really low inductance, 0.8 mH say, they would do better than your more 'powerful' steppers.

Often steppers that have very high holding torque also suffer from high inductance. If you were going to replace them
look for motors of less than 2mH or better still 1mH. If you can't find a specification for inductance or a speed-torque
diagram then walk away, they are being pitched to newcomers, and you are not. If the manufacturer or supplier cannot
supply a spec then they are rubbish.

One way to counteract the negative effect of inductance is to increase the voltage of the driver. Gecko, Leadshine and
other leading manufacturers offer drivers capable of 80V.  Were you to use one of those drivers
and 70-80V power supply your existing steppers would go a lot faster before losing steps.

https://www.geckodrive.com/g203v-digital-step-drive.html
http://www.leadshine.com/productdetail.aspx?type=products&category=stepper-products&producttype=stepper-drives&series=AM&model=AM882

What you have discovered is that your particular steppers with the load of your gantry have borderline sufficient
torque to maintain steps at 400 rpm with your current driver. With either lower inductance steppers and/or higher
voltage drives and power supply you might find you could double or triple that limit.

Its not impossible that the kernel speed of Mach3 is limiting the rate that steps can be taken, but this occurs when you
have made an unrealistic choice of microstepping. Further your description of the symptoms and noise suggest losing
steps not any limitation on the behalf of Mach but rather just the plain loss of torque at speed.

Craig
My wife left with my best friend...
     and I miss him!
Re: Stepper motors that shudder.
« Reply #9 on: April 02, 2019, 08:35:28 PM »
Quote
in your case
425 oz.in. Inexperienced buyers tend to focus of holding torque. Savvy buyers on the other hand look for the inductance
of a motor, the lower the inductance the better because the motor will run faster with less torque degradation.



Craig. Now that, is a fantastic piece of writing. That, is EXACTLY what was in my mind when I bought my motors. "Oooh yeeer, gotta be 425oz.in or they cant be any good" Ha. Ok I am armed with some good information and will go forth to bring my gantry into line.

Many thanks