Random x-axis failure (video included)

Dear fellow reprappers,

we have completed our Prusa i3 around Christmas and since then are bugfixing the hell out of it, mostly playing with software setting (e.g. slicing setup).
Though, there is one issue that bugs us a lot. The x axis randomly, well, fails to move, and I'm not sure how to explain this issue. Also, we have extensively searched on possible causes for this problem, but didn't find any.

- x axis makes loud noise and fails to move/moves uncontrollably
- usually lasts for 1-3 seconds
- seems to be more often when printing the first and last few layers (though I am not sure)
--> causes the print to go wrong, if not immediately paused, homed and resumed

Yesterday, unpleasantly around midnight, this issue came again and wouldn't go away, which I thought was a good thing, since I was able to capture it on camera.
Please watch this video, and watch it with headphones on:
[www.youtube.com]
Note that first I have only clicked in one direction (yes, x plus and minus are switched, but this works fine), and the carriage should only move left. As you can see, it moves whereever it wants.
Later, I try to drive home manually (when I film from below). When I tried to home x, it gets really nasty. Forgot what I did afterwards, but doesn't seem to matter, since every command results in pretty much the same.


What we have tried in order to solve this:
- made sure that mechanically nothing is stopping it
- made sure the driver doesn't overheat, using a 40mm fan pointed directly at it (though I didn't use one yesterday, when I did, the failure came just as often as without)
- reduced the acceleration in Marlin to very low numbers (see our config file: [www.dropbox.com])
- turned the pot down a lot and up a lot, didn't make a difference either
- checked the pulley and idler, seems they run perfect
- replaced the x driver with a spare one without success
- switched x and y motor, which didn't help; the other motor produced the same error
- checked the cable for good connection, which it should have
- switched RAMPS for a replacement, didn't work either

When moving the carriage around by hand it works just fine. Also, most of the times, it prints nicely. It seems to be a case of badluck that it randomly goes on strike.

Because I really don't know how to explain this issue, I wasn't able to find any helpful advice. If someone knows this behavior and can help us, we would be so thankful!

Edited 6 time(s). Last edit at 01/18/2015 10:40AM by Bonscha.

Watched video
you should really get a tripod or some type of mount
camera jiggling around makes it almost impossible to diagnose.

Looks like x motor problem.
Adjust x driver pot to mid point
and adjust with tiny movements.
see Current limiting under
[www.pololu.com]

[www.youtube.com]

X axis wires
1. --- move wires around -- different route - twist, away from other wiring. (cable crosstalk, short)
2. replace with higher gauge wire
------- some shielded twisted pair --- CAT5 cable would do

Do you have access to a scope to see X-Axis output

you could put 12V LED across each phase and watch LEDs blink

I am betting on wiring

Have you tightened the belt enough so that it can be plucked light a guitar string?
I could be belt slipping.
When you pluck the upper section of belt it should produce a dull twang.
Is the pull tight
Are well talking about the X (the bed) or Y the section the head moves along?

Edited 1 time(s). Last edit at 01/19/2015 01:57AM by GRAYWOLF.

@cozmicray:
Thanks you watched the video. I have now used two pairs out of a CAT5 cable, hope that is sufficient for testing purposes. I will test it while printing later, until now it seems to work...
If it works I would want to switch the cables for all motors so everyone has a sufficient cable.
Do you think LiYCY 4x0.25mm² will do? Or do I need LiYCY (TP) or higher gauge? Any other suggestions for a failsafe system?
I should be able to get pretty much every cable
Also, what to to about the mess of cables on the RAMPS board? Don't they interfere there?

@GRAYWOLF:
Belt should be tight, I did look for that again and again. Pulley doesn't slip either. I have to use brute force to stop the carriage (in order to produce the same sounds), which I don't see can be caused by the mechanics.
The x carriage drives a lot when failing, and it changes direction randomly, say when trying to home it will just drive left and right and stay somewhere then.


If this all doesn't help, I have a video filmed from two tripods with two cameras, one dedicated for pulley observation and one for the nozzle/carriage. I'll upload that, then, so you can have a better look.

I would use:

18 4 AWG 18/4 1FT Stranded Shielded Wire Cable for CNC Stepper Motors

[www.ebay.com]

I just calculated the cross-section for the motors.
Given 1.33 A @ 12 V and a maximum length of one meter, we would need around 0.012 mm² for a motor.

I think I will look up LiYCY-OB 4x0.14 (~AWG35/36), which is especially flexible and only 4.3 mm thick.
Think that'll do? I can't tell if the ebay cable is inflexible...
I would get 100 m of that cable for 20 Euros...

Hey I use cable like the 18/4 I recommended all the time
plenty flexible

I don't know what LiYCY-OB 4x0.14 (~AWG35/36) is ??? but 36 AWG.
carrying 1.2 A?

Perhaps you should use wireless motors for NO flexibility problems at all?

What are all these calculations? Did you consider relativistic effects
and magnetic deviation and effect of LHC on it?

Power supply close to motor may be doing it?

Put a piece of ferrus material between motor and power supply

But then again check out LHC schedule?

Printer seems to run smoothly. I'm now trying to print as much as I can to test it. And to finally get something done
Hope the problem is solved with rewiring it


Calculation for cable cross-section:

A = ( 2 * L * I * cos ) / ( y * Ua )
where
A = cross-section
L = cable length (1 m, more should never be required)
I = amps (1.33)
cos = efficiency (1 for DC)
y = conductivity (56 for copper)
Ua = voltage drop (3 % are 0.36)

This gets me A = 0.13 mm².
The cable I found is strongly shielded; It is a dedicated control cable.