I need help with a different kind of 3 stepper z axis.
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I know it is possible to use 3 steppers to level your bed as part of the z axis, but I am wondering if it is possible to set up a bed with two motors being used for leveling and then a third motor being used for the z-axis (the z-axis is on the print head with the bed staying in relatively the same spot)? Is this do-able?
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@BismuthBlues Yes, this should be do-able. Do you have a Z probe, or does each of the bed levelling motors and Z axis have an endstop? How much movement would the bed motors have? I think so long as it has 10mm, it should be fine.
One way to do it would be to home the Z axis in the centre, using a probe. Then redefine the Z axis with M584 as the two bed motors, and use the normal two-motor Z levelling to level the bed. Possibly define the print head motor to be another axis during this, so you can move it if necessary. Then switch back the Z axis to the print head motor. Using the conditional G code of RRF3.0.1 would help!
I'd think the main problem would be that you are leaving two motors on continuous hold, in one position, for as long as it's printing. I'd be tempted to have some mechanical locking mechanism, so you can turn off the two bed motors once levelled.
Ian
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@BismuthBlues I'm finding this difficult to imagine. The way I read it is that you want to have 2 motors (presumable driving some sort of lead screws) to adjust the bed plate, then a third motor to raise and lower the gantry holding the XY axes in Z. So the two motors will only be able to tilt the bed in one direction. Or do you plan to have the 2 motors (screws) forming two corners of a triangle, with the third corner being a "fixed" pivot point? I guess that would work.
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This is excellent! I had this idea a couple of months ago and am wondering the very same thing! I don't think it's been attempted yet? I'm still building the printer I want to try it on. I'm quite excited by the idea and glad to see someone else is wanting to try it too.
The idea for me was to have tiny steppers mounted on the bed frame for levelling only as you described. As if they were in place of manual levelling screws. The cost saving vs three full z screws would be significant if it worked. An alternative for large beds would be 2 full screws and one levelling motor which is what I'm going to try. The BLV MGN I'm building is designed with 2 z screws.
The way I imagined it was as @droftarts described by using M584 to define then redefine or hide the extra motors after levelling. I've ordered some very small stepper motors to try and i guessed ideally you would get one with worm drives which drive a spur gear centered on levelling screw. This would help with the issue of motors being constantly on as they would be near impossible to back drive. I couldn't find worm drives suitable but I ordered a couple of each of the following to try, at least as a proof of concept.
https://www.aliexpress.com/item/4000033935971.html?spm=a2g0s.9042311.0.0.36e14c4dDzdDE9
https://www.aliexpress.com/item/32974500234.html?spm=a2g0s.9042311.0.0.36e14c4dDzdDE9There's issues to solve, these might be too weak, also driving them with 5v brings complications. I'm a little wary of hooking up 24v and seeing what happens. For the price though I figured why not just grab them and work the rest out later.
I'm itching to see if you manage to implement this, I'm a few weeks off yet, still building and missed the chinese new year break.
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@littlehobbyshop said in I need help with a different kind of 3 stepper z axis.:
also driving them with 5v brings complications. I'm a little wary of hooking up 24v and seeing what happens
Voltage is a very slippery concept when driven by a driver that controls current. Personally, I wouldn't hesitate to hook them up to 24V, if the current is set below the limit of the motor.
Example: I am running Nema 23 motors that don't actually publish a voltage spec, but you can "back calculate" it as being in the 3 to 5V range ... and I'm running them at 70V. This is on a 24" x 60" x 5" router that has made thousands (tens of thousands?) of production cuts.
My bigger concern would be if they have enough torque to actually move the bed. I'd go with something more like this:
Two of them for $2.82. Certainly cheap enough.
Or even just a Nema17. Very proven. A small holding current will lock it.
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@Danal Appreciate that, not tried running steppers on higher voltages. Agreed on the torque, I have a Nema 17 and another unknown stepper floating about the workshop, just wanted to have a go with the tiny ones. I think the planetary geared one is favourite.
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@littlehobbyshop said in I need help with a different kind of 3 stepper z axis.:
@Danal Appreciate that, not tried running steppers on higher voltages. Agreed on the torque, I have a Nema 17 and another unknown stepper floating about the workshop, just wanted to have a go with the tiny ones. I think the planetary geared one is favourite.
It might be fun to go smaller and smaller and see what happens. The little ones certainly are cheap enough, and given the long lead time, ordering several variants to play with makes sense.
Keep us posted.
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@littlehobbyshop Just bear in mind that 2 points define a line and 3 points define a plane. So to level a bed (which is a plane) with 2 motors, you need to have a pivot point which isn't adjustable in Z, then arrange the motors so that their position forms an equilateral triangle with the (fixed) pivot. Or use 3 motors.
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@littlehobbyshop @deckingman I actually was toying (briefly) with the idea of just using one. There would be a pivot point, and then one stepper that when turned counter clockwise would raise one corner, and then clockwise would raise the other corner. When the corner would raise too much, it would fall to a point lower than the level of the pivot point. I quickly decided against this because it seems like way more effort than it would be worth.