Progressively weaken Stepper Motor

Hello and thanks in advance.

I purchased the Huxley kit from techzone, but am having trouble with one of the four stepper motors. It seems to having almost no holding strength and the problem is getting progressively worse.

The stepper motor is installed to control the x-axis (the one with the X/extruder-carriage) and is unable to move the carriage at any speed.

First, I marked the shaft of the stepper motor to make sure it was not spinning freely within the gear. I also checked that the belt was not slipping over the belt.

The motor get hot (but not uncomfortable) to the touch and was measured with an IR thermometer at 45-50 externally.

The across both the the red/blue and green/black, I measured the resistant at 7.6 ohm. Which is the same as the other steppers.

Also test the holding force by manually trying to turn the stepper motor will powered. The suspect motor turns with almost no force (almost as if it was off). The other motors could be turned but it was somewhat difficult.

The x-carriage does require the most force to move as compared to the other axis, but it is still pretty easy to move.

Lastly the wiring to the monolith board is identical to the other three axis.

I'm at a lost... Is the stepper motor going bad or demagnetizing? Is there something I can do to salvage the motor? Any guidance would be most appreciated?

Kassie

In such cases it's always a good idea to swap motors and/or stepper drivers between axes. Does the motor weaken if it's connected to the Y-axis? You get the idea.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

Thanks for you repIy! I should have thought to do this earlier.

Anyway I swapped the connections to the electronics, in other words the Y-axis electronics connected to the X-axis motor and visa versa, and that made no difference. The motor could still not move the x carriage. I had the same result with the y motor connected to the x-axis. So I'm pretty sure it's not a matter of having a faulty stepper motor, but rather with friction.

I see two types of action. First, trying to reduce the friction. Second, Upgrading the stepper. Regarding the second, I cann't find a datasheet for the steppers (i'm asking techzonecom about this). The only information I see is a label on the side that says PN:sa423903ss-02 and Lot: 201102 Does anyone know about these steppers? Is the holding force reletively low compared to other high torque steppers used in repraps?

I also still have a few question I regarding failing stepper motors.

How common is it for a stepper motor to fail/what is the life span, if current, volt, and temp keeps with specs?

How do they fail and how do I troubleshoot? I have read about the coils shorting and I am assuming that checking the resistance across the coils is the best way to troubleshoot this. I have also heard of them demagnetizing in regards to disassembly (http://www.cnczone.com/forums/general_electronics_discussion/3848-how_scrap_your_steppers_servos.html), but no much about what this looks like.

I was concerned demagnetization, because when I attached my steppers the screw pushed 3 of the 4 screws used to hold the case together out. Should I still be concerned about that stepper?

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Second, Upgrading the stepper.

You mean, sort of a brute force attack? That's a considerable idea in an army battle, but in civil mechanics you should find the reason for that high friction. High friction also means high wear and high inaccuracy, after all.

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Generation 7 Electronics	Teacup Firmware	RepRap DIY

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You mean, sort of a brute force attack? That's a considerable idea in an army battle, but in civil mechanics you should find the reason for that high friction

Good point! I completely agree that upgrading the stepper is not the ideal option. BTW I love the metaphor.

I'm building a techzone huxley myself currently. Havent tried moving axis with motors yet, actually one of my very next steps.

Did you set up some appropriate motor current level by turning the trimpots as recommended in the Monotronics assembly instructions ?
Too few current might be the problem. I recommend using a multimeter, the temperature trick seems a bit too unprecise IMO.

Another idea to maybe try, to losen every nuts in the x-axis a bit and see if that helps, and then tighten back the nuts one by one to find where is the friction.

DeuxVis Thanks for your comments and I wish you well in you build. When you get to the extruder, make sure to have a few extra hand. I've been through about 6 so far, not all of them die from of my mistakes.

I have a few I ideas about the cause of the friction, but didn't bring them up here because the is a forum about steppers (I'm new to posting in forum so I was worried about proper etiquette and may be a bit to conservative).

Anyway, I noticed that there is a slight (very slight) bow in x axis rail that has the bushing. I think it formed because some of the parts of the x axis didn't fit very well, one of the rods has a bit of squeezing tension on it. I am not sure how big of an issue it is but it's something to tear down and see if I drilling out some of the parts will settle it down. Regardless I was about to do several prints even with this issue at speed 18 mm/s (faster would skip steps and always in the same place in only one direction..)

Second, I used a light oil lubricate on the x-axis, notice that graphite from the bushing started being left on the rail. This made me feel rather uncomfortable with the lube so I try to stop using it until I had something with PTFE in it. Anyway I think time caused the oil to got dirtied and actually increased the friction. Over time I had to reduce my print speed to 9 mm/s and eventually that didn't work.

Third, at one point trying to get my stepper motor to work at 9 mm/s again pushed the pot up a tiniest hair. That drastically increased my heat maybe around 60 C ( a bit to hot too touch be not burning if you try... I didn't actually measure it). Before I realized the heat was to high, my motor mount warped about 2 mm.

Regarding the trim pots, I agree that the touch method of checking for heat is a bit imprecise but I can say from my experience it's actually not as bad as I would have thought. Based on my understanding and experience with this machine, the goal is to push the line were the motor get hot but not hot enough to damage the plastic. That being said I noticed almost no difference in actual torque with increases with the trimpot. As the wiki says

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temperature rise is proportional to the square of current, but torque is directly proportional so you can keep temperature under control without losing too much torque.

When I originally set up my electronics I followed the wiki but used the multimeter suggestion. This got me into to ball park but I realized that one of my stepper was just a wee hot at approx. 55C measured on my cheap IR thermometer.

I will look into loosening nuts. My hope is that will be enough to help with my rail deflection.

Edited 1 time(s). Last edit at 07/19/2011 10:11AM by Kassie.

Hi Kassie.

I know this is an old thread, but did you get your x axis to work properly? I have just assembled my Techzone Huxley and I seem to have the same problem with sluggish x axis (the motor seems to have af weak torque). I have tried looseing all bolts and i have even split the bronze bushing (as the manual suggests).

Any help would be appreciated.

Regards

I ended having the problem too, my X axis seems to have run "sticky" on some parts of the course of the carriage after some use.

I'm working on a solution based on linear bearings and changing the X axis smooth rods, will let you know how it goes.


Just as a side note, god damn the non-metric system users !