Second dead stepper in a week, coincidence?

I've been getting a recurring issue with my printer and it has me scratching my head! Hoping I can get some help diagnosing the root cause.

Whats:
X axis was having issues where it would cut out mid print, causing it to lose x position. The other axes would continue to function as normal. Got worse over time.
Rambo 1.3 electronics
Repetier Firmware
Printer Type: MendelMax 1.5
x axis is 8mm smooth chromed rods with self aligning bronze bushings
Nema 17 stepper

What I've tried:
I added a fan on my Rambo
I swapped the X axis with E2 via the firmware ---> problem persisted
I turned down acceleration and speed ---> problem persisted
I physically switched X and Y axis ---> problem persisted

All signs point to it being the motor. So I switched out the motor with the one extra I had in a box and the problem went away!!!
Or so I thought...

Problem came back. I ran through all the diagnostics again and all signs again pointed to the stepper motor. I was just so lucky to have bought a new extruder with a smaller Nema 17, so I had the old standard Nema 17 ready to go. I swapped the motor out again, and the problem is gone!

So another thing I will add is my X-axis motor runs very hot, and I recently realized that Repetier firmware sets the digipots in % instead of 8-bit (0-100 instead of 0-255). I've had all of my steppers set at 55, I was able to turn my X axis down to 30 and it runs noticeably cooler and hasn't skipped any steps yet. Could anybody shed some light on why some motors are running hotter than others if they are set at the same current setting? Z does not run hot, probably because there are 2 motors in parallel. My Y axis does not run hot at all. My extruder is a bit warm, but nothing crazy. When the X-axis was set at 55%, it was very hot to the touch. So I think I was burning my steppers out. But why is it getting so hot?

Another thing that I noticed: My X axis has been very noisy and causes a lot of vibrations. I ran a test sequence with the old bad motor, it just moves the x axis back and forth a couple of times, it was very noisy. I switched out with the new motor, and the X-axis was silent! Sure, sometimes it will hit a resonant frequency, generally at the lower-mid speeds. But it was like night and day. So now I've been running the printer for a couple of hours and I'm starting to hear those vibrations return, which has me worried that I'm about to destroy a 3rd motor! Granted, basing anything off of the vibrations right now is a bit tough becuase I'm running a print, so it's not a direct comparison. I've never been able to figure out what is vibrating so much, it kind of drives me crazy but I've grown to accept it. On top of this, I've had this printer for years and I've never had this vibration problem before.

What could I be not thinking of?

Aaaaand I'm going to go insane. It has started happening again. Less than 4 hours after replacing the 2nd motor. Now that I've turned down the current and the motor is very cool to the touch, it couldn't possibly be an overheating issue. I don't think it was a mechanical missed step, definitely didn't catch on anything in the print.

Is there any possibility that firmware can be doing this? I'm running the dev version of Repetier... though it doesn't explain why everything goes back to working when I replace the stepper!! Very discouraging. I love RepRappin but I'm growing so tired of my printer always being broken.

This can sometimes be caused by an intermittent connection to the Controller Board from the Motor I had a similar problem some time ago on a I3 where the vibrations would cause a short disconnect and thereby causing missed steps In my case it was the Y Motor so I would double check that all the pins in that connector are making good contact and are tight.

HTH

Doug

Thanks Doug. Forgot to also mention that I had inspected the wire to board connectors, all the crimps and all, and even went through with soldering a little bit just to ensure the wires were in good contact. I've also tried testing out the connection by wiggling the connectors mid print. Violently and angrily. No response. Also, the first motor had its own connector and wire. When I installed the second motor, I had to splice a completely different wires to it. For the 3rd motor I am using the same wires.

Are you sure it's wired correctly? That is the only thing I can think of that might cause the noise and heat. Or the axis is not moving smoothly, but I guessing you have checked that already.

I'm not so sure about the wiring. My understanding is there are 2 coils on a stepper, and just so long as you pair them up it should work out? Then if the direction isn't what you want, you can either swap the wiring or invert through firmware. Is there more to this?

yes they need to be paired, but there is also a positive and negative (sort of).to each pair. is you have both running the same direction. if you swap one pair the motor will fight with itself. you just need to reverse one pair. If things get worse then it was wired correctly.

Quote
cat.farmer
yes they need to be paired, but there is also a positive and negative (sort of).to each pair. is you have both running the same direction. if you swap one pair the motor will fight with itself. you just need to reverse one pair. If things get worse then it was wired correctly.

That's not so. If you reverse the wires in a phase, all that happens is that the motor runs in the opposite direction.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].