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Z-axis steppers not working - possibly dead from over current?

Posted by JasonStonier 
Z-axis steppers not working - possibly dead from over current?
February 11, 2021 08:09AM
Arduino Mega with RAMPS 1.4, A4988 drivers, 12864 LCD controller, and NEMA 17 motors. Marlin firmware.

A while back I bought a cheap Anet A8 printer that never worked well due to its terrible tolerances, so I built a frame with decent linear sliders and transferred the motors and some mechanicals over to it, with a new RAMPS 1.4 board and Arduino Mega clone.

While setting up and testing, I ran each motor using the firmware's "move axis" function - no end stops or heaters etc attached, and the motors were all free running - i.e. not attached to belts or lead screws yet.

X and Y motors moved fine, but the Z-axis motors were just vibrating - usually a sign of low current to my understanding.

I slowly increased the current pot on the driver board until the motors kicked in - then realised one was running backwards. Without switching off power (yeah, I know) I pulled one motor and reversed the cable - and neither motor has worked since.

Here's what I have done:

1) Swapped the A4988 for the unused one from Extruder 2
2) Tested other motors on that 'new' driver - they work fine
3) Tested my Z-motors on that new driver - they vibrate
4) Tested each Z-motor individually on that driver - they vibrate
5) Tested each Z-motor on OTHER axis drivers - they vibrate
6) Swapped cables - the 'Z' cables on other motors work fine

One thing I noticed is that the original A4988 that was on the Z-axis - the adjustment pot just rotates freely with no start or end stop - so I think it was faulty out of the box.

My guess is that the motors are dead due to an over current - but that's a pure guess. I don't know another way to test the motors other than in this RAMPS board, so not sure what else I can do to isolate the problem.

Any advice from the hive mind on this one? Thanks.

Edited 1 time(s). Last edit at 02/11/2021 08:11AM by JasonStonier.
Re: Z-axis steppers not working - possibly dead from over current?
February 11, 2021 09:41AM
Give the motor a sniff. If it doesn't stink, it is probably fine. It's really hard to kill a motor.

The tiny driver modules, on the other hand, will die if you look at them wrong. Get a bunch of spares- you're going to need them. When you get tired of replacing them, consider a controller board that has motor drivers soldered on the board for thermal management.

Son of MegaMax 3D printer: [www.instructables.com]
Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]
Re: Z-axis steppers not working - possibly dead from over current?
February 12, 2021 09:12AM
Great advice - thanks for that.

You gave me some confidence to keep going with that motor and I found that the driver board was dead, AND that there were combinations of cables and motors that just didn't work - I now have all the axis motors working.

My next question - and I have searched for this but I suspect I don't know the right terminology to search for - the X and Y motors are really quiet, but the Z motors are very loud in operation - a kind of grinding hum, and sending 10mm of movement results in about 80mm or so of travel on the lead screw. Now, I haven't calibrated it yet so that might be a red herring - but could the noise (and the extra travel) be to do with (micro)stepping? I have all three jumpers in for 1/16th stepping.

Again, any advice gratefully received.
Re: Z-axis steppers not working - possibly dead from over current?
February 12, 2021 01:37PM
On my 3D Printer I have dual Z-Stepper motors an need almost double the V-Ref Current to properly get the Parallel steppers to work.

My Setting as reference only.
V-Ref current single stepper motor 0.495
V-Ref current Dual motor 0.895

What are your settings on this line

Edited 1 time(s). Last edit at 02/12/2021 01:38PM by Roberts_Clif.

Computer Programmer / Electronics Technician
Re: Z-axis steppers not working - possibly dead from over current?
March 30, 2021 11:18AM
Since this question I completely redesigned the printer - now using dual Y-axis steppers, and a single Z-Axis stepper to lower the print bed. My Y-axis motors, I wired in series and it seems to be working perfectly (mechanically - haven't actually printed anything yet). I'm not sure what the downside of wiring in series is, really - only low torque, but it would seem that can be designed around.
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