I parameter to M906 and Motor Currents

PDBeal

I parameter to M906 and Motor Currents
August 07, 2016 11:43AM

Registered: 7 years ago
Posts: 558

As I've been setting up my largest CoreXY machine, I had to increase the I value of M906 for the Z axis. Otherwise it drops like a rocket when things go idle, so for a while I've been running with

M906 X800 Y800 Z1400 E800 I100;			; Set motor currents (mA)

I know this means 100% motor currents when idle, but it has me wondering is there any benefit to changing the above config to:

M906 X800 Y800 E800 I30;				; Set motor currents (mA)
M906 Z1400 I100;					; Set motor currents (mA)

Or is the motor idle current not motor independent?

Edited 1 time(s). Last edit at 08/07/2016 11:43AM by PDBeal.

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dc42

Re: I parameter to M906 and Motor Currents
August 07, 2016 05:47PM

Registered: 10 years ago
Posts: 14,672

Currently there is just one idle current factor, applied to all motors.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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deckingman

Re: I parameter to M906 and Motor Currents
August 08, 2016 03:06AM

Registered: 8 years ago
Posts: 622

Just stumbled across this thread. I didn't even know there was an idle current factor. What's a good number to use and/or how does one go about determining it? Thanks.

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selva_tvi

Re: I parameter to M906 and Motor Currents
August 08, 2016 06:40AM

Registered: 9 years ago
Posts: 54

I hope this will clear your query.

[reprap.org]

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dc42

Re: I parameter to M906 and Motor Currents
August 08, 2016 09:52AM

Registered: 10 years ago
Posts: 14,672

Quote
deckingman
Just stumbled across this thread. I didn't even know there was an idle current factor. What's a good number to use and/or how does one go about determining it? Thanks.

You want the current to be high enough to hold position, but otherwise the lower the better to keep everything cool. The default 30% works well for typical Cartesian printers. Deltas may need higher, so may Cartesian and CoreXY printers with ballscrew-driven Z axes.

Edited 1 time(s). Last edit at 08/08/2016 02:12PM by dc42.

Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

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PDBeal

Re: I parameter to M906 and Motor Currents
August 08, 2016 10:16AM

Registered: 7 years ago
Posts: 558

Yea, my Z axis on my CoreXY are belt driven, and if the current isn't at 100% at idle, the Z axis will drop a few seconds into a pause print meaning it is not resume-able.

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deckingman

Re: I parameter to M906 and Motor Currents
August 08, 2016 02:09PM

Registered: 8 years ago
Posts: 622

Quote
PDBeal
Yea, my Z axis on my CoreXY are belt driven, and if the current isn't at 100% at idle, the Z axis will drop a few seconds into a pause print meaning it is not resume-able.

Ah...........now it makes sense. I was wondering how your Z axis could drop. The bed on the one I'm building weighs in at about 7kg so I went for triple 8mm x 1mm pitch screws, single motor, one continuous belt. It just sits wherever I put it with no power so I guess I could use a really low idle value (moving it is another matter entirely smiling smiley

)

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PDBeal

Re: I parameter to M906 and Motor Currents
August 08, 2016 08:11PM

Registered: 7 years ago
Posts: 558

Aye, I'm using 1 big long belt also, with the aluminum profile bed, 3d printed mounts for the bed springs/screws. No idea what the weight is, but considering it takes the 1.4A current to move it and hold it through all it's travel I have to imagine its not light by any means. And to cover those oops moments when I download the config file, there are springs to catch it at the bottom.

IMG_0707.JPG

Edited 2 time(s). Last edit at 08/08/2016 08:23PM by PDBeal.

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