Motor Currents?

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Noircogi
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Motor Currents?

Postby Noircogi » Sat Mar 03, 2018 2:18 am

I've been printing at the "recommended" max speed of 100mm/S and had a terrible time getting layer shifts on larger items. I was also seeing the extruder popping back as well (not slipping but actually turning backwards) unless I ran the hot-end temp really high. That was very easy to trigger just by running a manual extrude at anything over 5 mm/sec.

I turned up the motor currents in config.g for X,Y,Z and E and it fixed both of those issues. The printer is slightly louder in operation though.

Are those 1 amp settings correct? I turned all up to 1.5A and the motors only get a bit warm, not hot at all.

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Re: Motor Currents?

Postby geneb » Sat Mar 03, 2018 11:37 am

I think it varies based on unknown factors. I say this because my Artemis stepper current is default across the board and I don't have any issues with skipping. I DID at first, but that was my own damn fault - I was not doing a Z lift on retract and the nozzle was smacking the part causing it to lose steps, which results in shifted layers.

My poor machine has spent 18-20 hours a day printing non-stop since last Sunday and was printing Atomic Gunmetal Gray PLA @ 198C at 100mm/sec. The only time it skipped is when I went to a different roll and had to bump the temp to 200C. (0.50mm nozzle)

If bumping your current to 1.5A works for you, run with it - it's not going to hurt the motors. You might try tweaking the output voltage to 13V and back the current down to 1A. That's what mine is currently set at.

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Re: Motor Currents?

Postby wepollock » Sun Mar 04, 2018 11:01 am

Based on this thread I just changed my M906 command in config.g

M906 X1080 Y1080 Z1080 E1000:1000 I50 ; Set motor currents (mA) and idle current %

I have used steppers (and stepper drivers) in several arduino projects. My perception is that current helps holding and voltage helps stepping.

Perhaps voltage helps stepping because you are going to have a faster current-response (increased flow rate sort of speak). Although the less sophisticated stepper drivers I have used in the past are more interested in current because current limiting to the motor will in effect drive voltage. I never had to think about voltage (In my projects, I did have to think about dissipating heat on stepper drivers and other components like LM voltage regulators.)

I am sure these sophisticated drivers have thermal protection; if you pump up the amperage are you could-theoretically heat up a driver to the point of shutdown. I am just suggesting to make incremental rather than radical changes.

I just checked the documentation on the power supply - it is tunable from 10-13.5.

IN watts @1 amp @ 13v you have 13W
In watts @1.2 amp @ 12v you have 14.4W
Watts is a measure of energy transfer or work done (joules/sec)

In watts @1.5 amp @12v you have 18W

I don't know "how material" any of these changes are going to be; the approach would be to [b]play around in small increments. After thinking this out a bit I backed into 13W; with a setting of 1080.. Have I changed anything that is really going to change the performance of the printer +/-.



PS I just found this good link;

What is good about this link is that it talks about inductance - The very sophisticated stepper drivers can manage inductance; perhaps when you increase the operating speed of the steppers you are putting more inductive resistance into play.


https://www.geckodrive.com/gecko/images/cms_files/Step%20Motor%20Basics%20Guide.pdf

dc42
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Re: Motor Currents?

Postby dc42 » Sun Mar 04, 2018 12:57 pm

The Duet can only change the peak stepper motor current in 100mA increments. The firmware is designed so that if you ask for a multiple of 100mA, you get what you asked for. Other values will be rounded up or down. So when trying different stepper motor currents, I suggest you choose multiples of 100mA.

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Re: Motor Currents?

Postby wepollock » Sun Mar 04, 2018 1:25 pm

Good to know 1100 it is. (@1100, qualitatively it seems like an improvement - it was quiet before and it seems even less noisy)


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Re: Motor Currents?

Postby JayDee » Mon Jun 04, 2018 3:06 pm

I can corroborate the need to play with especially extruder current limits; mine (totally stock) was skipping terribly when I first got it. I goosed it up in increments until it didn't skip any longer, then added 100mA to that value just for some insurance. I don't see any downside, and none of my motors get more than warm even on long prints.

Currently, I've got this config: Motor current (mA) - X:1200, Y:1200, Z:1200, E:1600

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Re: Motor Currents?

Postby dc42 » Tue Jun 05, 2018 10:01 am

JayDee wrote:I can corroborate the need to play with especially extruder current limits; mine (totally stock) was skipping terribly when I first got it. I goosed it up in increments until it didn't skip any longer, then added 100mA to that value just for some insurance. I don't see any downside, and none of my motors get more than warm even on long prints.

Currently, I've got this config: Motor current (mA) - X:1200, Y:1200, Z:1200, E:1600


I don't know what motors SeeMeCNC use in the Artemis, but I generally recommend setting the driver current to between 60% and 85% of the rated current. Going up to 100% or even a little more is OK for the motor, because the motor current rating is normally specified with both phases energised, whereas with microstepping drivers only one phase gets the full current at a time.

Generally the drivers will work without fan cooling at 2.0A current and below, if the Duet is mounted somewhere that air can circulate easily. If it's in a confined space, you might need fan cooling for the Duet at a little less than 2A.

The drivers have both over-temperature warning and over temperature shutdown protection. Unless you are using very old firmware, when the drivers signal a warning (which is 20C before they shut down), the firmware will generate warning messages. The warning messages are delayed for a short while if you have a fan configured to turn on when the overheat warning is produced.

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Re: Motor Currents?

Postby JayDee » Tue Jun 05, 2018 12:51 pm

Good info David, thanks.

The Duet is in the top sheet metal cavity of the Artemis, and while there is a fan in the stock config, I've found that keeping the metal cover on dramatically impacts my WiFi reliability, so I run it with the cover off. There's good air circulation in my environment and I've never had a temperature warning, but I'm not really pushing the envelope of motor currents either.

The motors in my Artemis, at least, are KL17H248-20-4AM, rated at 2A per phase.

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Re: Motor Currents?

Postby wepollock » Mon Jun 11, 2018 9:12 pm

good observation. my rostock max with duet in an external 3d printed box gets far better wifi connectivity vs the artemis...

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Re: Motor Currents?

Postby JayDee » Wed Jun 20, 2018 3:46 pm

My WiFi reliability with the Artemis is so bad that I recently purchased the wired Ethernet version of the Duet.


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