Prusa/RAMPS 1.4 worked for months, no longer good prints

Hi. Not sure where to post this problem, but I need help. I'll try to be succinct.

- Configuration is a Prusa based on Arduino ATMega 2560, RAMPS 1.4, NEMA17 motors, Sprinter firmware, Slic3r (various versions), a fan constantly pointed at the stepper driver heat sinks
- Prints were quite good for several months
- Recently, I started having problems. So, I retreated to the 20mm calibration cube file from the RapRap site, so that I could better understand what is happening. Please see photo - I won't bias you by what i think, beyond the problem stemming from y movement without any x movement, y movement without enough x movement, etc. One interesting thing of note is that several months ago, the printer would skip x steps, resulting in the print subsequently shifting over (the printer was unaware of these missed steps). The fan directed towards the stepper driver heat sinks fixed this problem. That is not the case here though, as the print never becomes mis-aligned.

Any help would be hugely appreciated! Thanks to everybody for reading this!

It looks like the extruder is pausing due to a hardware problem. First thing i'd check is that the hobbed bolt is clean - if it's teeth are full of plastic dust it'll slip randomly. Check there aren't visible jumps in the gears movement - that would indicate over/under current or excessive friction, or a loose extruder motor wire. It's also possible your hot end is jammed with debris - clean it by heating the nozzle to around 100C, then slowly pulling out the filament by hand. It'll need a decent amount of force, but at that temperature you can usually slide out the non-molten plastic, bringing any dirt with it. You should probably also check e steps/mm are ok, but the intermittent nature of that picture suggests it's roughly ok.

Hi James, thanks for your response. Did you notice that the extrusion never actually stops, just one of either the x or y axes stops moving? So, for example, instead of the 45 degree line you would expect from the infill in this photo, I get the 45 degree line to turn into either a vertical or horizontal line, all the while the extrusion is evenly deposited. This is why it seems like one or two of the motors are randomly kicking out, then back in.

Those are crazy moves. It seems to me that with such wild errors, that the only way the print could NOT get mis-aligned as you say in your first message would be if the gcode was produced that way - as if your slicer was doing that - but I can't imagine why that would be.

Do you have any older gcode files laying around that had previously produced accurate prints? It might be interesting to see if they still do. Otherwise I'm baffled.

I am a bit concerned about your statement that you need a fan on the stepper drivers. That sounds to me as if you're driving the motors too high. Perhaps the drivers have been damaged over time from the heat, but again if you are dropping steps, the print would be mis-aligned.

Could be false triggering of the X end stop due to noise. Is it always when X is moving in one direction?

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[www.hydraraptor.blogspot.com]

jbernardis Wrote:
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> Those are crazy moves. It seems to me that with
> such wild errors, that the only way the print
> could NOT get mis-aligned as you say in your first
> message would be if the gcode was produced that
> way - as if your slicer was doing that - but I
> can't imagine why that would be.
>
> Do you have any older gcode files laying around
> that had previously produced accurate prints? It
> might be interesting to see if they still do.
> Otherwise I'm baffled.

Hey, thanks very much for your comments. Yes, I totally agree. In fact, it was from reaching the same conclusion that I returned to this 20mm cube GCode file, which had produced perfect results in the past. However, I'll try another in case I inadvertently created a new version accidentally, or in case this one was misfiled.

>
> I am a bit concerned about your statement that you
> need a fan on the stepper drivers. That sounds to
> me as if you're driving the motors too high.
> Perhaps the drivers have been damaged over time
> from the heat, but again if you are dropping
> steps, the print would be mis-aligned.

In the past, I had dropped steps on the x axis, everything shifted to the left from that layer onwards. I was already using the lowest pot value that would permit reliable movement. Somebody mentioned that the drivers might be getting hot, so I began using a fan directed towards the RAMPS board. The step skipping problem vanished. I removed the fan, it came back. I returned to fan employment, the problem was eliminated once again. So, I concluded that the advice was correct, and this was just required. Perhaps this was just masking another problem? If a driver connection were loose, could that increase the resistance and lead to excessive heat build-up? I purchased a pre-assembled board from Ultimaker by the way. This doesn't imply that there are no bad solder joints though, of course.

The weirdest thing is that I was starting to think that all the y movements and x movements, instead of acting together (like a zipper), were instead all getting grouped, so all the y movements happened first, then all the x movements. Hence, no missed steps, but a vertical then horizontal line instead of one diagonal line. If that were the GCode, I could see it, but given that it was using a known good GCode calibration file, I decided that this could not be.

I'll collect some additional data and get back to this thread with any new information.

Again, thanks so much!

nophead Wrote:
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> Could be false triggering of the X end stop due to
> noise. Is it always when X is moving in one
> direction?

Thanks for your response nophead!

I believe that it is in the increasing x direction only (but I will check and respond afterwards).
I will try disabling the max position x end stop in the firmware, in case that is the issue, to determine the effect.

Given that the erratic behavior started at approx. layer #3, and all of the subsequent perimeters are properly aligned, would you agree that neither x nor y steps are being missed altogether?

Is there any mechanism in the firmware you can think of that would turn a diagonal into its orthogonal components?

@nophead: You were nearly exactly right. It was indeed false end stop triggering. However, it was not due to noise. It was due to my being a _____ (fill in appropriate derogatory term here). See photo attached.

10 months ago, when I assembled my machine, I installed endstops. My x-axis had insufficient range due to the connectors for the end stops hitting the x-axis bracket. As such, instead of using connectors on the x-end max endstop, I tightly twisted wire through the holes and around each contact. I meant to solder it once I verified that it worked properly, but I didn't. I am fully aware that this was a chump move, and I highly appreciate both your time and that of jbernardis.

Many thanks to both of nophead and jbernardis!

Edited 1 time(s). Last edit at 12/28/2012 10:47PM by spacey123.