Stepper motors should hold position when error.
- tommylight
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21 Oct 2025 21:27 #336852
by tommylight
Replied by tommylight on topic Stepper motors should hold position when error.
In your case, you should have gotten a servo/stepper with brake for Z axis.
It is a hardware feature, so software can not help, but if the loop is closed in LinuxCNC at least it will know the position.
PCW's idea with enabling fast after fault and if loop is closed in LinuxCNC is very good.
As for your question, drive fault will disable the motor in the drive, so nothing LinuxCNC can do about it (except above), and so will LinuxCNC disable everything when it gets a fault error.
It is a hardware feature, so software can not help, but if the loop is closed in LinuxCNC at least it will know the position.
PCW's idea with enabling fast after fault and if loop is closed in LinuxCNC is very good.
As for your question, drive fault will disable the motor in the drive, so nothing LinuxCNC can do about it (except above), and so will LinuxCNC disable everything when it gets a fault error.
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- LeonDolnicar
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28 Oct 2025 16:23 #337350
by LeonDolnicar
Replied by LeonDolnicar on topic Stepper motors should hold position when error.
The z axis motor does have a brake but there is s delay between the motor going dead and brake engaging. In that delay time the z axis drops a couple centimeters.
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28 Oct 2025 16:25 #337351
by LeonDolnicar
Replied by LeonDolnicar on topic Stepper motors should hold position when error.
I will try this, but again this will introduce a delay. Currently when the motor disables the brake enables but there is a delay so z axis drops a couple centimeters.
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29 Oct 2025 20:53 #337411
by PCW
Replied by PCW on topic Stepper motors should hold position when error.
If the drive itself drops the holding current on a fault,
you are always going to lose position, there is really
nothing LinuxCNC can do about this.
How far it drops depends on how fast the drive can be
reset or brake applied. LinuxCNC can react very quickly
to a fault signal (< 1 ms), but I would expect the external hardware
(brake or drive reset) to be slower.
you are always going to lose position, there is really
nothing LinuxCNC can do about this.
How far it drops depends on how fast the drive can be
reset or brake applied. LinuxCNC can react very quickly
to a fault signal (< 1 ms), but I would expect the external hardware
(brake or drive reset) to be slower.
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29 Oct 2025 22:05 #337416
by tommylight
This seems like to heavy, so it would need a counterweight, and if so, it will also cause to much stress on the motor and drive trying to keep all that weight in position. Also mitigated by said counterweight.
Replied by tommylight on topic Stepper motors should hold position when error.
How heavy is the Z axis?Currently when the motor disables the brake enables but there is a delay so z axis drops a couple centimeters.
This seems like to heavy, so it would need a counterweight, and if so, it will also cause to much stress on the motor and drive trying to keep all that weight in position. Also mitigated by said counterweight.
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31 Oct 2025 20:31 #337599
by LeonDolnicar
Replied by LeonDolnicar on topic Stepper motors should hold position when error.
I dont think the weight is the problem maybe more that the ball screw is fast. 20mm per turn. I got a good quality rexroth ballscrew so I used it. Because of the faster screw I used a stronger stepper motor 12Nm nema34.
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31 Oct 2025 20:48 #337601
by tommylight
Replied by tommylight on topic Stepper motors should hold position when error.
Still, the counterweight would solve your existing issue, and not hard to implement.
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