Z stepper issues

[Tim]

There was a similar topic in this section, but I'm not sure if the issue I'm seeing is the same or not. My Z axis motor is, from time to time, just failing to go up. When I turn on the printer, I can do "home Z", and it homes just fine. Then after a bit of up/down movement from "jog controls", it will suddenly stop going up, but just go down, except noisily. This happens under both pronterface and S3D. Apparently it's happening as the motor heats up under use. This is the original Z-axis stepper motor from the 12/19V series M2, which was known to get very hot, so maybe it has just reached the end of its lifetime early. Definitely not a problem keeping everything lubricated, as I do that regularly. It's just weird the way it works fine for 20-30 seconds or so after power-up and then suddenly switches into this mode where it is unable to lift the bed any more. Does this mean I need a new Z axis stepper motor?

[jimc]

Tim, there was a point in time when something changed in the m2. I assume its just voltage settings for the z stepper because older m2 z steppers would get hot. Mine which is still a 19v machine has a z stepper that barely gets above room temp. I would imagine that the hot ones would have a decreased lifespan. There isnt much there that i can think of that would cause your issue assuming everything is lubed and you can lift and lower the bed by hand and feel no binding. The only thing left is stepper or voltage settings in marlin......or a wire issue

[Tim]

It's not a wire issue because it's always working on power-on and always failing within a certain time after I start jogging the Z axis position---so I think it's very likely an issue with the motor failing when it reaches a certain temperature.

I think that the Z axis motor model was changed, but I'm not at all certain. I'm using the same firmware and software as everyone else, so it can't be that. It's possible that it has something to do with the RAMBo board revision (with the older, 8-microstep stepper drivers), but because they have the same driver chip on all the motor channels, that seems unlikely; although the Z axis motor is different from the others in that it is always under load. Mine has always been hot enough to burn you, probably up around 80 to 90 degrees C.

[Tim]

Ed Nisley has a very good run-down on his SoftSolder site about why the M2 Z axis motor is the wrong kind and why that causes it to run hot. From that I would conclude that the motor model was changed. For me (as well as Ed), an ohm-meter across the green and black wires gives a winding resistance of 28 ohms. I'm curious what the resistance is on motors that don't run hot. There's no identification on the motor, unfortunately.

[jimc]

yeah you have the hot one. i remember when i first got my m2 the big ad on thing people were designing and posting on thingiverse was fan ducts to cool that motor. when i got mine and felt the motor i couldnt understand what all the fuss was because my motor was cold. in fact its by far the coolest motor on the m2. all the heat cant be good for longevity of the motor. it sounds to me like its probably just time. you know the deal.......time to email karen!!!

[Tim]

time to email karen!!!

Already have. . .

[ednisley]

why the M2 Z axis motor is the wrong kind

Basically, steppers come in two flavors:

• High resistance for simple full-step H-bridge drivers
• Low resistance for current-limiting microstep drivers

The RAMBo has microstepping drivers, so a high-resistance motor isn't appropriate. Shortly after I pointed that out, MG started using the right motor: M2s shipped after late summer-ish in 2013 are OK.

Grisly details:
http://softsolder.com/2013/04/10/makerg ... per-motor/

Motor ID & good comment discussion on acceleration:
http://softsolder.com/2013/04/11/makerg ... s-numbers/

Replacement motor & discussion of wiring:
http://softsolder.com/2013/06/28/makerg ... ransplant/

With that installed, I could goose the Z axis acceleration & speed to run with the XY axes. It can't go as fast, because the leadscrew gears it down, but now it easily lifts the platform and doesn't glow dull red...

[Tim]

With that installed, I could goose the Z axis acceleration & speed to run with the XY axes. It can't go as fast, because the leadscrew gears it down, but now it easily lifts the platform and doesn't glow dull red...

Pronterface and slic3r always ran the Z motor at very slow speeds. Probably it was doing reasonably well with the 19V power supply and the slow speed. Then I abused it first by running Simplify3D, which ran it at high speed, and then by upgrading to the 24V supply. That's why, while you were seeing temperatures up around 60C, I was seeing temperatures that were probably closer to 80C, maybe even higher. I should probably be surprised that it lasted as long as it has on the 24V supply.

[Tim]

For the record: If you have a M2 that shipped before mid-2013, and the Z-axis stepper motor reads ~28 ohms between wires 1 and 3, and the stepper motor gets very hot when it's running, you are highly discouraged from upgrading to 24V.

If you choose to upgrade to 24V anyway, you should either replace the Z-axis stepper motor with an appropriate (low winding resistance) one, or install a fan that does nothing other than blow directly on the stepper motor, the latter option which may or may not buy the motor some additional days of life.

[jimc]

good info for sure. are you all squared away now tim?