Good Grief: X-Stepper Motor Cable Failure

[David Kessner]

Good grief!  I just figured out how to get my strangely warped platform leveled, and just figured out the design flaw with the thermocouple (and how to fix it) when my X-Axis Stepper Motor cable died!  A while back I did the preventative care for this part (removing the rolled steel pin, replacing it with a cut zip-tie strain relief thing.  But it failed anyway.

(Rep2, for those of you following along at home.)

I fixed it by cutting out a section of the old cable, along with the cable for the limit switch, and spliced in a new section of 10-conductor ribbon cable.  I then draped the new cable in such a way as to allow for a lot of flexing without pinching.  The minimum radius bend (that flexes) that the cable should endure is quite large.  I am not done, but the pictures below shows the current state of things:

This first pic shows how the cable drapes straight down from the gantry and makes a "U" shape back up to the corner of the frame.  The cable is a little bit long in this picture, since it shouldn't touch the floor of the build area.

The next two pics shows how the cable currently attaches to the gantry, as well as all my heat-shrunk splices.  

    

At the moment, the other end of the "U" is just jammed into one of the pre-existing plastic cable clips.  To do this properly I should make a bracket that attaches to the frame and allows for a proper drape of the cable.  I will do this soon, since I just got the bot back up and running.  However, the two zip-ties on the gantry end actually work quite well and I do not see having to make something "better".  I should, however, tidy up the splices so they don't touch the draped cable.

[Bottleworks]

It's funny how these cables weren't an issue with the replicator 1. They changed it, and now they're problematic. It will be something that I will be modifying on the first day I get my replicator 2.

[Chris Milnes]

My Rep2 is currently dead until i get the replacement x axis cable as well. 

[David Kessner]

Jetguy:  We've all had bad days (and I'm not sure which of us had the bad day, might have been me).  I'm willing to put it behind us if you are.

While I think that pressuring MBI to "do the right thing" is a good goal, and one I fully support, I did not want to wait for them to come out with proper fixes for the thermocouple and X-Axis cable problem.  It took them something like 3 months to release their own Upgraded Extruder fix, and they only did that after WingCommander shamed them with his superior solution.

At the moment, I honestly doubt that MBI has the engineering chops to properly fix the TC and X-Axis problem.  

Part of my motivation for figuring out the TC issue was:  1. It is in an area that I have expertise and was qualified to contribute back to the 3-D printer community.   And, 2. Clearly MBI didn't know what was going on, so someone had to show them the way.  My hope is that it helps to shame MBI into action. Until then, at least the Rep2 users will have an alternative way to fix their bots so they are not dead in the water.

I was hoping that the X-Axis cable fix would be similarly easy.  But the way that the cables and connectors are done, it isn't something that a normal person at home could do themselves.  My hacked solution requires 16 splices, and most people couldn't do it well.  (Of course, Rep2 people are a different breed!)  To do it the correct way would require remaking the whole wiring harness and it requires special crimping tools to do.  MBI better step up to the plate quickly on this one!

-DK

[David Kessner]

I recommend at least buying the parts and having them on had for when it does fail.  

On Tuesday, April 2, 2013 11:55:33 PM UTC-6, Wingcommander whpthomas wrote:

So it seems the strain relief may have delayed the failure - but failure appears to be an inevitable outcome.

I am going to start looking into this a bit more - not that I don't already have a long list of things to do already :(

[Jeff Johnson]

Yeah, I'm waiting on a new cable myself. My Rep 2 is only ~ 30 days old and it went bad. Took 5 days for them to respond to my ticket, its now 10 days later and still no part (even though they agreed to send one).  I jury rigged mine as well, I had to cut out the bad section and resolder it and just have the cables hanging, so that at least I can print. 

To anyone who wants to buy one of these, be prepared to troubleshoot and improvise. 

Jeff

[Steve]

David, JetGuy:

Can the X-Axis stepper cable be replaced with a standard 10 wire ribbon cable with connectors on .1" centers? 

If so, how long of a cable should I buy?

I am trying to get a collection of spare parts for the Rep2. I have a spare nozzle, spare extruder mods, spare fan, and spare build plate. I would like to buy a spare X-Axis cable for when that fails. I am also looking for a place to get the insulation material that is taped above the print nozzle.

It took three weeks to get an obviously warped build plate replaced. Four days to get an email answer which requested more info, which resulted in another four day delay, then they wanted the original build plate sent back before shipping the replacement, which took another twelve days. Anyway, since uptime is important to me I am trying to collect my own set of spares.

Steve

[David Kessner]

No, a standard ribbon cable with connectors on 0.1 inch centers will not work, for several reasons.

On the stepper motor end, the connector is a little different than most you might be used to.  Each individual wire has the contact crimped onto it, and then that is pushed into the plastic connector housing.  For you to do this yourself, you would have to find the exact connector used and buy both the housing and the contacts-- and then buy the special crimp tool made for those contacts.  Normally the crimp tools are somewhere in the US$100 to $250 range.

There is a similar (but different) connector for the end-stop PCB.  You still crimp on the contacts individually and push them into a plastic housing.  But because the connector is different, you need a different crimp tool.  Another US$100-250.

(Disclaimer for the pedantic:  I didn't really price out the crimp tools, I am basing this on the last time I looked for a similar tool for a different connector.)

The motherboard end is super stupid.  It does use a standard dual-row, 0.1 inch center, header.  But it uses a single connector for all stepper motors.  The ribbon cable is then split apart and different sections run to different motors.  What this means is that to replace one stepper motor cable you need to replace all stepper motor cables!  (Note:  I do not recommend trying to carefully replace just the section of the cable that goes to the X-Axis motor, as you'll have crimping issues at the motherboard end that would result in unreliable connections.)   There is a similar all-in-one connector for the limit switches, so you can't replace only one.  You need to replace all of them.  Ugh.

For someone who is handy with a soldering iron, it is much easier to just cut out a section of the X-Axis cables and splice in a slightly longer piece of standard ribbon cable.  This means that you need to only "stock" some ribbon cable and heat shrink tubing.  

[Steve]

David:

Thanks.

I have ribbon cable so I will just plan on splicing the X-Stepper cable when the time comes. Did you have any trouble determining where the break was, or did you just cut near the stepper and again near where it goes into the frame?

Steve

[David Kessner]

I have not done an autopsy on the bad cable yet.  I cut the stepper motor cable as close to the connector as I dared while still leaving room to do the splice.  Around 2 inches, I think.  Since the end stop cable wasn't broken, and it needs a little more room anyway, I cut it a little longer.  

I have about 6 inches of extra slack in the cable now.  Meaning, after the new routing of the "U", I have an additional 6 inches of cable that I need to stuff somewhere.  I suggest that when you do your mods, you leave a similar amount of extra cable.  It is a little bit of a pain to deal with, but it is better than finding out that you made everything too short.

[Steve]

David:

Will do, thanks.

Steve

[Dan Newman]

> There is a similar (but different) connector for the end-stop PCB. You
> still crimp on the contacts individually and push them into a plastic
> housing. But because the connector is different, you need a different
> crimp tool. Another US$100-250.
>
> (Disclaimer for the pedantic: I didn't really price out the crimp tools, I
> am basing this on the last time I looked for a similar tool for a different
> connector.)

And from my experience, there's a world of difference between the inexpensive
crimp tools and the expensive ones from Amp/Tyco, etc. The expensive ones
will give you sticker shock but WILL last a lifetime (and have warranties
that reflect that). The inexpensive ones will just frustrate you to no end.

Dan

[Eighty]

To answer the length question: when I replaced mine, the longest portion came in almost exactly at 1m (the X section). So if you're ordering a section of ribbon, that's the length to replace. But it probably would be a good idea to get a bit extra...maybe 42" or so.

[David Kessner]

So I did an autopsy on my broken stepper motor cable.  In that cable there are four conductors, and all four were broken.  The break was right where the cable exits from the "tunnel" just above the stepper motor.  If the rolled pin was still in place, the break would be at the edge of the pin closest to the rear of the bot.  

I also looked at the end-stop cable and found that it was close to breaking.  Just by feel, I could spot where the break was about to happen.  When stripping the insulation off of the cable, the conductors broke.  

There is some interesting conclusions that can be drawn from this:

1.  The rolled pin itself probably doesn't play into the ultimate demise of the cable.  If it did, then the conductors closer to the pin would fail first.  Since all four conductors failed at roughly the same time then whatever force broke the cable would be evenly applied to all conductors.

2.  When the gantry is farthest back, the cable has the sharpest bend on it.  It is likely this bend, every time the bot zeros the axis's, that broke it.  The zip-tie strain relief does not address this failure mode.

3.  While I have not seen any end-stop failures in the message boards, it is only a matter of time.  If you are replacing one cable, you should also replace the other one.

I do think the zip-tie strain relief does help-- it just doesn't help enough.

-David

[Dan Newman]

> 3. While I have not seen any end-stop failures in the message boards, it
> is only a matter of time. If you are replacing one cable, you should also
> replace the other one.

Early on, MBI attributed Rep 1 motherboard deaths to a failed X axis endstop
cable. I believe that to this day, when they send you a new Rep 1 motherboard,
they also send you a replacement X axis endstop cable. (They sent me one a
couple of months back.) Now, a couple of comments

1. This was the Rep 1 motherboard. The Rep 2 motherboard is far more robust.
I am NOT trying to suggest that this will harm Rep 2 motherboards.

2. Failing X axis endstop cables is most certainly not the only cause of
death of Rep 1 motherboards. Indeed, some capable people have inspected
their X axis endstop cables as part of post mortems and found the cables
to be in good shape with no shorts. So, some Rep 1 deaths by cable, but
not all.

Dan

[TobyCWoods]

Then it is likely we will almost all have the cable failure eventually. OBOY! 

[Eighty]

My solution to the bending issue was pretty basic. After replacing the harness, I put a couple of tight winds of blue painters tape around the ribbon (at the flexure point), the theory being that it will stiffen the ribbon there. So far so good, but it takes a lot of printing to see if it actually works.

[Karas Kustoms]

I just repaired my x axis and end stop cables. Once I removed the end stop cable, it stopped working, so it got the cut and patch job as well. Looks like crap, but still works. I like David's solution to the problem, looks nice and tidy. Hopefully this will be addressed and we can get a more permanent fix. Until then I am glad you all are around. Thanks guys!