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vnks

UMO Skipping steps on long prints, tried everything

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Hi all,

I have an Ultimaker Original that started skipping steps on long prints (10+ hours) a few months back. Since then, I've tried everything I could think without making much of a difference. Pretty much the only thing I haven't tried is swapping the steppers. When it skips, it's a bunch of steps at once, like the driver overheats and shuts down. My test case is a 20+ hour print, slow, at 40 microns, so that I don't waste too much filament. I always oil the axes first, movement is smooth all over, no obvious binding. It always skips on the X-axis.

- Replacing the stepper drivers, swapping X & Y - no change, same problem on the X axis.

- Tuning stepper drivers, lowering or increasing the current, no noticeable difference until it's raised too much and it skips more.

- Loosening the belts, long ones and short ones.

- Marking the bushings and rods, to make sure nothing slips - they're not slipping.

At this point I'm out of ideas, I'd swap the steppers if it wasn't such a pain, but I'm not even sure it's possible for the stepper itself to cause this. I did build my own firmware a while back (custom heated bed), but this was long before the problem started and I haven't touched it since.

Any ideas? At this point I'd probably hook up a thermistor to stepper driver heatsinks and start logging the temperature, just to confirm that the drivers are really overheating.

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How's the cooling? Is the fan running properly, is air getting to the drivers? Maybe try running it without the cover on the electronics and directing a large PC fan or similar on it to see if that makes a difference? (you can let it print while the printer is on its side)

 

The fan is running fine, it's oiled and produces plenty of airflow. Additionally, whenever I catch it in the act of lots of skipping, if I shut down the print and take off the cover, the driver heatsinks are barely warm.

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If you increase the current and the skipping gets worse then you most probably damaged the driver already (I did so with a driver from UM). Replace it and be careful to set the current not too high (something like 1.1-1.3A is reasonable).

 

I've swapped the drivers around, and have a bunch of new StepSticks I've tried as well, no difference - it keeps happening on the same axis.

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Have you tried swapping the x and the y motor yet? I mean not only on the Ultiboard but physically...

 

That would be quite involved, I'd either have to re-wire everything or cut and re-splice the wiring... I'm not sure it's possible for a stepper motor itself to cause this - they're basically solid state. I certainly haven't been able to find any confirmation that it could be a potential cause.

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You have to identify which component causes the problem. For this you have to switch components between the axes. Remote diagnostics is very difficult; only systematic trial and error will bring you closer to a solution...

 

Yeah, I've been doing it for close to two months now with no progress. I was hoping someone has experienced this with a unique root cause - I've already tried all the common ones.

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Here's one weird thing I noticed, the head bearings are shifted on the X-axis, same axis that's skipping - http://imgur.com/sdX2dkZ . There's a matching gap on the other side. Could this be a symptom of a hardware issue? Everything feels very smooth, especially after oiling.

 

My ultimaker 2 just started doing this too on the same axis as yours.  I hear a clunk then suddenly the x axis is off by a few mm. i had to leave so I couldn't diagnose it but I found this thread and was surpised that it is from today. It is pretty hot in there right now (93 degrees) which might be part of it.

Edited by Guest

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Ok I'm home now and it's hitting the side of the printer. I'm printing something that just barely fits, with a brim. Cura thinks it's ok but on the right side I noticed the brim line was overlapping the previous one so it wasn't moving far enough to the right.. then after a few brim lines it moved outward a bit more and smacked into the side of the printer.. so i guess I'm not having the same issue. I guess Cura has some bugs ;)

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Ok I'm home now and it's hitting the side of the printer.  I'm printing something that just barely fits, with a brim. Cura thinks it's ok but on the right side I noticed the brim line was overlapping the previous one so it wasn't moving far enough to the right.. then after a few brim lines it moved outward a bit more and smacked into the side of the printer.. so i guess I'm not having the same issue.  I guess Cura has some bugs ;)

 

Ah, too bad. In my case it probably happened a while ago with a larger model running into the same issues as yours. I think I'll try getting good quality stepper drivers instead of the cheapos I have now, there's some timing support for this being the problem...

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So, after getting branded black Polulu stepper drivers, and replacing all of them, I have the same exact problem - skipped steps on the X-axis during long prints (6+ hours). Current is set to 1.15 amps, no heatsinks (per documentation, none are needed for this current level with active cooling).

I noticed that all the skips are in the same direction - it keeps shifting towards the left, if looking at the printer from the front. Is this data point ringing a bell for anyone? I have nothing else left to try other than replacing the main board on a whim :(

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I have the same problem, and was also convinced that it was an electrical rather than hardware problem. However last night I witnessed it happening, and it was caused by a bind on the mechanical system. I'm not sure how or where yet but I do know it was totally stuck. Once I got it moving again it was silky smooth with no indications of binding anywhere. I think it may be going off-square somehow and binding like that. Or there is something caught in the bearings? I'm ordering new rods and graphite filled bearings today, hope to sort it with that.

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I've come to the conclusion that in my case there's oil-soaked wood dust in the linear bearings, that needs to be cleaned out. I haven't had a chance to actually do it yet, and won't for a while, but it makes a lot of sense to me. The printer was sitting in a pretty dusty wood shop, and I can see the grime inside the bearings. When I oil the rods, everything is smooth for a while, but a few hours in the dust absorbs the oil, and everything binds up. I'm going to disassemble everything and soak in WD-40 or something along those lines to get it all clean, and keep it away from wood dust in the future. Hopefully that'll be it.

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My x motor ended up failing not too long ago. It had the same symptom you described where it suddenly skipped a few steps and finished the print with everything on the top shifted to the left. A few prints later the motor seized up completely. They sent me a new one under warrantee. I was able to break the bad motor loose with some oil and turning it by hand. Getting the motor off is easy enough. I would just replace it.

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