Steppers with Brakes
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I have setup with Z motors and a descending build table. Is it possible to add an option to control the brake on the stepper?
The brake is switched on all the time until the voltage is applied to it. Then the stepper is free to move.
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Do you mean that you have a stepper with a physically separate brake?
Because a 'standard' stepper has only its own magnetic "cog" when the power is off, and its "holding torque" when the power is on. Nothing else.
Duet can't do anything when the power is off.
You can configure how long the motors keep power with the M84 command, and how much current they have (and therefore holding torque) with the M906 command.
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No, I mean steppper with an electromagnetic brake. The brake is always activated. In order to start the movement, it is necessary to provide power to the brake - usually 12 or 24V DC.
So when the power is turned off the stepper is stopped. -
Do you have a link to this hardware?
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@dep what voltage needs to be applied and what voltage are you running your system at? Also how much current does the brake circuit draw when the break is disengaged? One simple option would be to use the output from one of the fan headers to power the break. as part of the printer start up you can turn that output on and release the breaks (once the motors have been engaged so the table does not drop). If not then you can use a spare expansion pin to control a relay or SSR to turn on and off the break circuit on command.
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@phaedrux said in Steppers with Brakes:
Do you have a link to this hardware?
There are many different models, for example this one:
@t3p3tony said in Steppers with Brakes:
@dep what voltage needs to be applied and what voltage are you running your system at? Also how much current does the brake circuit draw when the break is disengaged?
My system run at 24V. In general, such a brake usually consumes not much in the unlocking mode - about 10 watts, so it's not a problem to connect it.
@t3p3tony said in Steppers with Brakes:
... as part of the printer start up you can turn that output on and release the breaks ...
That's the question. I can of course write this down in macros or even plug a mosfet to the ENABLE pin of the motor. But will this be correct?
Maybe it will be possible to provide such an option in the firmware?
Because i have, for example 3 steppers on on Z axis and 3 endstops. -
Ahh I just realised this is in the firmware wishlist section! In the short term as you say you can use a macro. As long as you are happy with releasing all the breaks at once then you can use one fan/expansion pin to control all three. If not then you will need to use three pins with three macros. The "enable" test points are not actually enable - we switched them to be the SPI CS lines so don't use those.
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@t3p3tony said in Steppers with Brakes:
releasing all the breaks at once
Yes releasing all the breaks at once will be good.
But I'm afraid for example, when idle, steepers may off by timeout. Or, you might not notice that the steppers' shutdown command will be added by the slicer.
Therefore it will be fine if this option will be in the firmware!
