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ex-parrot

Safety of running E at 1500mA on UM2?

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You can quite easily determine that:

If it runs very hot, it's bad. If not, no problem.

Very hot means you can't touch it longer than a second or so.

Note that 50-60°C (which is hot, but you can touch it for 1-2 seconds) is normal operating temperature for most power-electronics.

/edit:

Make sure that you protect yourself against http://en.wikipedia.org/wiki/Electrostatic_discharge when you touch the electronics!

Discharge your body by touching a grounded piece of metal (like the radiator of a heater, or a metal doorframe, or the metal case of your computer).

 

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I ran across a couple posts related to changing the current on the extruder stepper. I have recently encountered a difficult-to-diagnose underextrusion issue, and want to explore current modification as a potential fix (or to at least determine if this stepper motor is part of the issue).

I am not, however, aware of how to change the current within the UM2's user interface. I am using cura 14.09 (and also looked in version 14.07).

How do I change the current for the extruder motor? (or what can I search for to help me find out how)? Is this a setting in the firmware?

Thanks!

 

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Yes, it's fw-controlled:

Maintenance - Advanced - Motion - Current E... if I'm not completely wrong...

 

That sounds about right but there you'll find the current for E to be restricted to values lower or equal 1300 mA. How do you bypass that limit and set the current to a higher value?

 

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You probably don't, unless you want to overheat the electronics...

If it is possible to set a higher current (that depends on how the reference voltage that sets the current on the driver IC is made), then you'll have to find and change the maximum current value in the source code and change it. Limits are usually hard-coded into Marlin's configuration.h

 

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The motors are have specifications that allow up to 1300mA. That's why the firmware limits it at this range. Running it beyond this range is at your own risk. (Aka, don't complain at us when you need a new motor)

Also, in tests we did, we didn't find more strength when going over 1250mA. So that's why the default it set to 1250mA. Also note that a significant factor for the UM2 feeder is actually the temperature of the feeder axis. By increasing the current to 1500mA you are putting more power and thus more heat into this axis and it will grind a lot easier.

 

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Maybe the drivers overheat at 1500 mA which makes them lose power?

I'm not that much an expert on motors & currents - having worked mostly with professional drivers that took care of that question automatically.

The only time I actuall had to set a motor current was when I had to set up a test stand for flexible cables. It was a larger motor (maybe NEMA23 or something) and a heavier moving setup. The thing was, that I could find the best suitable current just by listening to it. Of course - current too low means no operation, but there was actually a very wide range where the machine would "work".

BUT, there was a difference in how the thing sounded when changing current. The more current I gave it, the louder the motor got. There were also some unusual sounds when setting the current too low (like stuttering, probably also some skipped steps).

So, I found the sweet spot by just listening to it and finding the spot where the machine sounded "happy".

I've only just started toying with the NEMA17 motors and pololu drivers (which I hate so much :p), and haven't had time to go in-depth there.

Got myself an easy stepper from reprap.me to make some tests, but I found my cooldrv DRV8825 drivers to produce a very annoying whistle with it, while the UMO drivers are silent but get insanely hot within seconds.

I'll be putting some work into making better drivers sometime in the next weeks because I see there's definitely a need for it.

 

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Whistle? You mean like a very high pitch? That only young people can hear?

I did some experiments with a new tinyG board that had 1/32 microstepping and the steppers were amazingly quiet but the young guy I was working with (Jaime from Ultimaker) was very annoyed by the high pitch. I barely noticed it but it seemed to be coming from the stepper motors. Although maybe I should have put my ear up to the board itself (or maybe I did and discounted it, I don't remember).

Is that what you are talking about?

 

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I didn't notice the noise until it was mentioned and then I had to move to within a foot of the extruder motor to really hear it clearly. I think it was 1/32 microstepping.

1/32 is much quieter than 1/16 but 1/64 is even quieter. I'm told.

 

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