GRBL Z axis issue.

Discussion about the arduino based g-code interpreter, grbl
groguard
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Re: GRBL Z axis issue.

Post by groguard » Wed Nov 12, 2014 2:31 am

Schruminator wrote:If it's still uncomfortably hot to the touch, it's going to go into thermal shutdown. Put a fan on it and cool it-- if it's still cool and you're having issues, then it is time to worry. For now, just figure out how to cool it.
I have a fan on it, but no heatsinks. There is a video in this post showing the fan.
Shapeoko 2 #3920. Nema 23's. Belt drive Z axis, ACME rod upgrade,
1m rails on X and Y, X upgraded to 60x40 extrusion with openrail, Mid span supports,
DW660 with Super-Pid, IC's DW660 dust shoe.
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Schruminator
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Re: GRBL Z axis issue.

Post by Schruminator » Wed Nov 12, 2014 2:34 am

Is it still hot? That's all that matters.

If it's still hot, you need to arrange your fan differently, put another fan on it or adjust your current. The whole goal is to get it cool to the touch, your problems won't end until that happens.

So, is it hot and is your fan blowing air directly onto the driver (towards it) or pulling air away from it? I'd recommend air towards it for a one fan setup.
1.8m x 1.0m SO2 #3638 / Vectric Aspire / ACME Z-axis / View my photography at http://www.mschrum.com

cvoinescu
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Re: GRBL Z axis issue.

Post by cvoinescu » Wed Nov 12, 2014 2:54 am

There has been a lot of bad gShields. I don't have any direct experience with a gShield, let alone one known to be from the bad batch, but my understanding is that one symptom is excessive heating of the Z axis driver.

That said, the chips can get very, very hot and still be okay. The die temperature for thermal shutdown is around 150°C.

The chip may be a small switch, but it switches 24 V at 2 A tens of thousands of times a second. A lot of the heat is generated during the transitions. The driver works and the motor draws power even when stationary.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

groguard
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Re: GRBL Z axis issue.

Post by groguard » Wed Nov 12, 2014 3:39 am

Schruminator wrote:Is it still hot? That's all that matters.

If it's still hot, you need to arrange your fan differently, put another fan on it or adjust your current. The whole goal is to get it cool to the touch, your problems won't end until that happens.

So, is it hot and is your fan blowing air directly onto the driver (towards it) or pulling air away from it? I'd recommend air towards it for a one fan setup.
I had the fan blowing across the board, Ive also tried with it overthe top blowing down on to the drivers. Still had the same problem.
cvoinescu wrote:There has been a lot of bad gShields. I don't have any direct experience with a gShield, let alone one known to be from the bad batch, but my understanding is that one symptom is excessive heating of the Z axis driver.

That said, the chips can get very, very hot and still be okay. The die temperature for thermal shutdown is around 150°C.

The chip may be a small switch, but it switches 24 V at 2 A tens of thousands of times a second. A lot of the heat is generated during the transitions. The driver works and the motor draws power even when stationary.
I bought it with the full kit back in April, could it have been defective this whole time? I dont think inventables would cover now. The Z axis always ran hot, I had the nema 17 severely low around .8 volts if I remember correctly.
Shapeoko 2 #3920. Nema 23's. Belt drive Z axis, ACME rod upgrade,
1m rails on X and Y, X upgraded to 60x40 extrusion with openrail, Mid span supports,
DW660 with Super-Pid, IC's DW660 dust shoe.
Build Log

cvoinescu
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Re: GRBL Z axis issue.

Post by cvoinescu » Wed Nov 12, 2014 11:03 am

The timing sounds about right, and switching to a NEMA 23 would have made it worse. As I understand it, the problem is that the capacitor for the charge pump that drives the gates of the high-side MOSFETs is the incorrect value (too small), so those MOSFETs don't switch on properly. That makes them dissipate much more power than they normally would, so the chip works more or less normally, except it heats up a lot.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

groguard
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Re: GRBL Z axis issue.

Post by groguard » Tue Nov 25, 2014 8:52 pm

Alright guys, so I got some heatsinks on there, and it didnt help still had the same problem. I ended up buying a new shield, and all of my problems are gone. Thanks for the help guys.
Shapeoko 2 #3920. Nema 23's. Belt drive Z axis, ACME rod upgrade,
1m rails on X and Y, X upgraded to 60x40 extrusion with openrail, Mid span supports,
DW660 with Super-Pid, IC's DW660 dust shoe.
Build Log

McOtis
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Location: Maryland

Re: GRBL Z axis issue.

Post by McOtis » Wed Nov 26, 2014 3:24 pm

How hot can the stepper motors themselves withstand?

I was having occasional Z axis issue, but those were resolved by increasing the current.
This of course increased the temperature of my driver and motor.
The driver I feel is welled cooled thanks to heat sinks and a fan, but what about the motor?

My stepper motor gets quite hot after a job; I measured it to be about 60 degrees C.
This that ok (standard NEMA 17)?

Schruminator
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Re: GRBL Z axis issue.

Post by Schruminator » Wed Nov 26, 2014 3:33 pm

I believe they can hit 80C to 100C based on the link below-- but that may be internal temperature and obviously the surface will measure cooler. My opinion is slightly different and I feel like 60C is too hot and either the current needs to be adjusted or you need to get some air flow across the stepper motor. I'm not sure what the exact temperature specification is before you start to have issues though.

http://reprap.org/wiki/Stepper_motor#Heat
1.8m x 1.0m SO2 #3638 / Vectric Aspire / ACME Z-axis / View my photography at http://www.mschrum.com

cvoinescu
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Re: GRBL Z axis issue.

Post by cvoinescu » Wed Nov 26, 2014 3:57 pm

Steppers are specified for 50 or 60 degree Celsius rise over ambient temperature (check the datasheet). So 60°C is fine.
Proud owner of ShapeOko #709, eShapeOko #0, and of store.amberspyglass.co.uk

Schruminator
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Re: GRBL Z axis issue.

Post by Schruminator » Wed Nov 26, 2014 3:59 pm

Is that internal temp or at the surface of the stepper motor? I'd be willing to bet that the heat transfer at the surface of the stepper motor is keeping those temps 10-20C cooler than the coil temps.
1.8m x 1.0m SO2 #3638 / Vectric Aspire / ACME Z-axis / View my photography at http://www.mschrum.com

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