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MMU2S selector motor never turns off  

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Aniraf
(@aniraf)
Eminent Member
MMU2S selector motor never turns off

It seems like my selector motor never turns off. It isn't moving, but it does seem to be vibrating and making a sound. It does this for hours before and after printing. It is usually a little warm whereas the rest of the stepper motors are cool when the printer is on but not printing. Is there any known issue that could be causing this? I couldn't find anything when searching. 

Posted : 24/08/2020 4:57 pm
jsw
 jsw
(@jsw)
Noble Member
RE: MMU2S selector motor never turns off

Many stepper applications call for the motor to be 'locked' in place by placing a constant current through the desired windings, and I'm assuming that they do this with the selector to hold it in the proper place for the selected filament.

It's normal for the stepper to get warm, but not extremely hot, when this is done, but it should not buzz or hunt.  It should be difficult to manually turn the selector when this is happening.

If you think it is an error, I would definitely bring it up in a support chat session.

Posted : 24/08/2020 6:52 pm
Aniraf
(@aniraf)
Eminent Member
Topic starter answered:
RE: MMU2S selector motor never turns off

@jsw

Great context thank you! It seems odd to me that during a "motors off" time the idler motor would be locked in any position. It doesn't do anything more than get slightly warm, but it does make a kind of feint hissing sound. Frankly it is annoying as hell and causes me to power down the whole printer. I otherwise wouldn't mind just leaving the printer on when I'm not using it. 

Is there a GCODE command that would "unlock" the stepper motor for the idler body? I tried searching for one, but it seems the MMU2S doesn't have that granular of commands.

Posted : 26/08/2020 9:25 pm
jsw
 jsw
(@jsw)
Noble Member
RE: MMU2S selector motor never turns off

I've never heard of a stepper making a hissing sound.  The only sounds I know of them making, other than the usual mechanical noise when they are turning, are a low hum if there is ripple in the power supply driving the motor, or anything from a buzz to a squeal to an almost musical tone if the stepper is physically restrained from moving but being commanded to do so.

The only thing I can possibly think of is that they are locking it in place with a pulse type of signal, instead of straight DC and you are hearing that or a (sub)harmonic of it as what you perceive as hiss.  I have not studied the firmware code for the MMU2S (on my do-it list, I assume it's available) so I don't know how they are driving the steppers.

As for manipulating the MMU2S directly with gcode, it's my impression that the commands to the MMU2S are given via a serial comm link between the main (Einsy) board and a separate control board on the MMU with its own firmware.  My hunch is that the commands are more of macro type things and there may or may not be a command (as you say, granularity) to simply power down the selector stepper, or a Prusa-specific gcode command to cause that command to be sent to the MMU.

Even if there was, I would be careful doing it, as the firmware (of the printer or the MMU or both) probably assumes known states and changing said states could result in uncertain results.

Posted : 26/08/2020 11:34 pm
Aniraf
(@aniraf)
Eminent Member
Topic starter answered:
RE: MMU2S selector motor never turns off

@jsw that makes sense. I know that the MMU seems to get "off" sometimes and it simply needs a reset for it to understand where it was in terms of selecting new filaments or recognizing the FIDNA. I am slicing using Prusa Slicer and I of course have the printer set with the MMU, then pushing that GCODE into Octoprint to drive the serial commands. That said, I can hear it right after starting even without connecting the Octoprint serial. 

 

 

Posted : 27/08/2020 1:23 am
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