Idle current reduction harmful when carving long lines?

[RohanSingh]

I’m trying to troubleshoot some minor deviations in my X axis. Tightening up pulleys and belts and V-wheels seems to have dealt with the issue, but it got me thinking— with the idle current reduction in the X-Controller, if I’m carving a long line that’s perpendicular to an axis, that axis will have reduced torque but will still be experiencing full load.

For example, consider carving a long, straight line from the “front” of a workpiece to the “back”, where the machine is only moving in the Y axis:

In this case, there is no movement in the X axis so, if I understand correctly, the X-Controller will reduce current to the X axis. Therefore, there will be less holding torque on the X axis, even though the carriage is experiencing load as it removes material. This would create the potential for slipping and losing steps.

I’m leaning toward completely disabling idle current reduction for this reason. Does anyone else have any input on this? Is there something incorrect in my understanding?

[WillWinder]

GRBL doesn’t disable any stepper motor unless ALL of them are idle for the step idle delay setting duration. It’s easy enough to set $1=255 if you want to double check anyway.

Some stepper drivers have a built-in thermal protection which could temporarily disable the stepper motors. I would be truly surprised if the X-Controller didn’t take this into account, but maybe double check that it has proper ventilation.

[RohanSingh]

Idle current reduction in an X-Controller feature, not a grbl feature. From the documentation:

Idle current reduction is another feature that can be set on the controller board. This setting automatically reduces the amount of current shortly after the motor stops moving, reducing heat from the driver and the motor. This feature is especially great for the Z axis which spends a lot of its time idle. You can set this using the dip switches, just make sure to again check out the diagram for proper placement.

Also check out this Inventables post by @BartDring which says:

The X-Controller idle reduction feature is different. It reduces current rather than stops current. It is also independent for each axis.

That’s what leads me to believe this could be an issue.

[JustinBusby]

@RohanSingh

with the idle current reduction in the X-Controller, if I’m carving a long line that’s perpendicular to an axis, that axis will have reduced torque but will still be experiencing full load.

Yes. If you’re moving only in the Y direction, X and Z loses torque. Similar goes for in the X direction, Y and Z lose torque.

@RohanSingh

I’m leaning toward completely disabling idle current reduction for this reason. Does anyone else have any input on this? Is there something incorrect in my understanding?

I disabled mine many months ago. I’ve made numerous posts on this same topic and I advocate most people to turn it off on all 3 axis.

I’ve also not had any heat related issues with it off.

X controler free axis movment

I just looked into this because I made the change to disable auto torque. With it enabled and no motion (the reduction circuitry is triggered off the X/Y/Z step lines), it reduces the reference voltage for the stepper driver to 30% of the set value from the pots (per the driver datasheet). That’s a pretty large reduction. In a “typical” carve, only the Z axis goes idle which may be okay since it is screw driven. But in a raster carve where you may have X or Y idle, that could introduce cut issu…

[HaldorLonningdal]

As long at the motor casings dont exceed 175degF they are all good.
If they heat above that reduce max current.

[JustinBusby]

The steppers only get warm.

The hardware is a different story. I’ve not measured/felt the Xcontroller but I’ve not gone into thermal shutdown either.

[JustinBusby]

The Xcontroller uses the Toshiba TB6600 chip as its driver. Your drivers are just heatsink and circuitry to interface to the same chip.

Given proper heatsinking and cooling, the chip is capable to drive 4A. If the heatsinking is insufficient, it may thermal overload at 1A.

That being said, the heatsinks on the Xcontroller look pretty sufficient and it should be fine. I’ll try to do a measurement next time I’m carving.

[RohanSingh]

@JustinBusby

That being said, the heatsinks on the Xcontroller look pretty sufficient and it should be fine. I’ll try to do a measurement next time I’m carving.

If you have the equipment and know-how to do so, I’d be interested in the results.

I’ve gone ahead and disabled idle current reduction on my machine for the X and Y axes. I left it on for Z, since it doesn’t seem to be an issue there.

[JustinBusby]

The inherent nature of the Z axis being screw driven does help that not care as much but it could cause some Z axis slipping as well. I recommend turning it off on all axis.

All your motors will heat almost the same. I use my Z axis stepper as my reference for if it’s too hot.

[RohanSingh]

That makes sense, I guess what’s good for the goose is good for the gander. I’ll go ahead and disable it on Z as well.

[RohanSingh]

Disabling idle current reduction and tightening some nuts and bolts seems to have gotten my machine back into shape. No more problems after several hours of carving.

I think idle current reduction is an anti-feature.

[JustinBusby]

Let’s face it, we’re all pushing our machines more than a normal/average user would.

A normal user, most likely, would not have any issues with the idle current turned on while running feed rates and depths that is Easel recommended.

Now, with Inventables pushing Vcarves and multi-stage carves, the dynamics of the situation changes. The carriage slipping on bit changes will become a CS problem and the easiest solution for that is to disable idle current reduction.