Disable Steppers... doesn't  

Re: Disable Steppers... doesn't

No, this is intentional by PR.

Re: Disable Steppers... doesn't

Maintaining Z axis power is intended to reduce the probability of the Z axis alignment slipping.

since the Prusa i3 was upgraded to use lead screws for the Z axis, the liklihood of the alignment slipping has increased significantly. so Prusa have made a effort to prevent this from disadvantaging the user.

Best wishes Joan

Re: Disable Steppers... doesn't

yes, it's not a bug, it's a feature.

➡ to keep the synchronisation between the right and the left z-stepper, it's required to "lock" them as good as possible.
this is done by keeping them "under power".

....but if the Z axis remains live, it's not 'enouigh'

what's enough and what isn't depends on what you are intended to achieve.

If you want to disable the steppers because you want to move the y-carriage freely, or just to avoid unnecessary power consumption, it does exactly what is required.

if your intention is to save as much power as possible, there's another option that you can select (not through the menu, but by using the interruptor at the psu).

Re: Disable Steppers... doesn't

yes, it's not a bug, it's a feature.

➡ to keep the synchronisation between the right and the left z-stepper, it's required to "lock" them as good as possible.
this is done by keeping them "under power".

If this would be true, then you would have to do a Z calibration each time you power on your printer. Or did I miss something?

Re: Disable Steppers... doesn't

Ok, thanks for the feedback, glad it's not a fault.

I'm fine with it going this, it's just that when I noticed that the printer could turn off the cooling fan on the extruder, something that my old printer did not do, I thought "that's nice, I can leave the machine turned on". But due to the Z motors being held under power, this isn't something I'll do.

It's not a problem, but I was intending to buy one of those FlashAir SD cards, and it would have been handy to be able to add a gcode to the printer from the sofa at any time, and print it later.

The thing is though, as Hendrik mentions, if I power off the printer to save wear on the Z motors (and quiet the noice from them, it's not load but I can hear the squeal made by the steppers/drivers) then this is the same as the printer "sleep" mode dropping the power. There's really no difference between the printer turning off the motors and me doing it, so where's the benefit to keeping them on?

Re: Disable Steppers... doesn't

If you power them down, and bump the Z, you will need to do a Calibrate Z before you print again (crash heads to top to align). Many of us leave the printer on (unless for an extend period of time) between prints so we don't have to do this.

Let's say you are removing a print, and will then print again right away. By keeping the Z energized, you don't need to do that step, even if you bump it when removing the old print. This feature save failed prints.

Re: Disable Steppers... doesn't

...
If this would be true, then you would have to do a Z calibration each time you power on your printer. Or did I miss something?

which is very well recommended, especially if you've turned the printer off and moved it.

Re: Disable Steppers... doesn't

...
If this would be true, then you would have to do a Z calibration each time you power on your printer. Or did I miss something?

which is very well recommended, especially if you've turned the printer off and moved it.

No, it is not. Josef does explain this in his video - you made me watch it again 🙂 -

There he tell why they are always on. It has been a long time since I watched this ... 🙂

So, they are powered on so that you don't mess anything up. You should recalibrate only if you moved it or put any pressure on the x-motor/idler.

Indeed I think this is not we implemented. The Bed levelling should notice that the X Axis has changed and ask for a new z calibration. The stepper should switch off with the others.

Re: Disable Steppers... doesn't

...
If this would be true, then you would have to do a Z calibration each time you power on your printer. Or did I miss something?

which is very well recommended, especially if you've turned the printer off and moved it.

No, it is not. Josef does explain this in his video - you made me watch it again 🙂 -

There he tell why they are always on. It has been a long time since I watched this ... 🙂

So, they are powered on so that you don't mess anything up. You should recalibrate only if you moved it or put any pressure on the x-motor/idler.

Indeed I think this is not we implemented. The Bed levelling should notice that the X Axis has changed and ask for a new z calibration. The stepper should switch off with the others.

I really would suggest you listen to Jeff's advice...

If you want the full picture, you have to listen to those using these printers day in and day out.

There is a big problem with stepper motors in that when power is removed, they tend to settle at a full-step position.

There are instances where steppers can settle at different full-step positions which will put your Z axis 40 microns out, and if this happens a few times, the tilt would be quite noticeable.

Peter

Re: Disable Steppers... doesn't

...
No, it is not. Josef does explain this in his video -...

that's the difference between what's recommended (by us) and what's required (in Josefs advertisement video).
➡ of course our prusa i3 mk2(s) can deal with a slightly misaligned z-height (gantry), because it does the meshbed levelling at the start of each print.

but Peter already mentioned the behaviour of the steppers:
💡 you need to know that the steppers can be driven in "full step" and "microstep" mode, depending on the type of stepper driver you are using.
the full step mode gives us a resolution of 200 steps per revolution (at an 1.8° stepper motor) but with microsteps you can control the motion of the stepper to "inbetween" positions. the rambo mini at our prusa uses allegro micro systems A4982 drivers, configured to control the motor with 16 microsteps. this means at a full rotation of the axis you can control the position with 3200 microsteps. at a full resolution the whole x-carriage moves up (or down) 8mm with our four threaded TR8x8 trapezoid spindle.
so if we do the math: each millimeter of height, could be controled by 400 microsteps.

🙄 but if you power the z-steppers off and on again, they snap to "full step" positions. so there might be a slight misalignment of up to (1mm/400)*16 = 0.04mm or 40µm, as mentioned by Peter.

the often you switch your printer off and on again (without using the z-calibration routine that levels both steppers) this inaccuracy may sum up.
ok, as Josef stated: our prusa usually can deal with this.... after the meshbed levelling.
😥 but: what if the misalignment is big enough so that the meshbed levelling would fail, because one of the 9 calibration points couldn't properly be detected anymore ?

in the best case your meshbed levelling simply fails and aborts 😥 ... but there are other behaviours reported if one of the points can't be detected properly 😮 .

➡ so I still recommend to use the Z-calibration after powering up the printer.... especially in cases where your x/y alignment isn't just perfect perpendicular, because in this case an even slight misalignment could easily lead to a failure during the meshbed levelling.

Re: Disable Steppers... doesn't

Z axis (gantry) misalignment isn't just uncomfortable, it's potentially catastrophic.

If it misaligns where the left side is lower than the right, it can cause the hotend to hit the bed before the sensor can detect it, leaving you with possibly a divot, a drag scar, and another drag scar when it starts trying to print with a completely hosed leveling result.

I've kind of noticed that some of you running 3d printers might have, I don't know, small children or animals running around your areas. Cat decides to jump up on your printer while it's off and *poof* the thing is unleveled. Or maybe your equipment handling is just plain sloppy.

PR can't control the environment that these things go into, so leaving the motors on is *kind of* a prudent thing to do.

I would personally prefer they not mess with the existing known g-code to implement this, but I suppose that's splitting hairs.

Re: Disable Steppers... doesn't

Ok, didn't know that you guys do Z calibration every time on power on. So far I personally did this only after maintenance work on the printer and had no issues so far.

I agree that when the stepper motors are reengaged they will snap to the next full step. And yes they might be a misalignment introduced. But I guess most of the time not: same motors by model and only one single stepper driver on the Rambo to control them both. And when switched off the motors should turn (if they do) in the same direction, thanks to mother gravity as long nothing put an noticeable extra pressure on one side.

Cool feature would be an auto correction of the XZ skew by moving one motor independently to align the axis, but this is not possible with the RAMBo mini without extra circuitry.

However a warning on Bed Levelling that the XZ skew has increased would be awesome.

Re: Disable Steppers... doesn't

It may already have this warning.
I powered on this morning and started a print. After warming, the bed levelling started, and on the third test point, it stopped. Error on the LCD stating that sensor triggered too early.
This mean that the right hand Z was lower than the left. A quick reset of the printer, long press on the LCD button, wind the carriage all the way to the top and restart the print, and everything works perfect again.

Thanks for everyones input on this one, seems there really is no ideal solution, but what we have is pretty close.