4 Z-Axis Steppers for a large build platform

Has anyone tried or has examples of a print bed that utilizes 4-stepper motors?

My custom repstrap has a fairly large print area, and while currently I'm only using a small portion of it, with a smaller bed,

I'm planning ahead as to how I'm going to achieve the larger bed.

Size is approximately 600mmx300mm

I was thinking 4 Steppers in each corner, where I could fine tune the leveling of the entire bed via a few step adjustments

I was just wondering the same thing.
(and just joined this forum/hijacked your thread to ask)


Helpful info:

The "Cartesio" 3D printer lifts its print-bed from all 4 corners, but with the use of just one stepper:
[reprap.org]

seen more clearly when viewing just the frame:
[reprap.org]


My biggest questions/concerns about using 4 steppers for the z-axis:

1. What are the chances of one of those motors missing a step (or micro-step)?
*i've got a rep-rap w/ 2 Z-steppers, but unfortunately the whole machine goes outta whack too quickly for me to determine whether or not having multiple z-axis steppers is part of the problem. Maybe some of the guys with quality rep-raps can chime-in about any problems they experience using multiple steppers for the z-axis.

2. What controller would you use?
*The only controllers I have seen thus-far seem to max-out at controlling 5-7 steppers? For example the Azteeg X3:
[reprap.org]
[www.panucatt.com]
- This thing can run up to 7 steppers, (if you use 4 for the Z-Axis, that doesn't leave you with much)... I'd like to find something that could handle 8-10 steppers.

Edited 1 time(s). Last edit at 11/06/2013 11:42PM by joshpit2003.

1) I would suspect the steppers wouldn't miss a step. They would have a pretty big mechanical advantage. I probably at first would also set the controller to hold the current.

2) I would just get use some extra pololu's.
Just set up the extra 4 on a bread board and wire them all to the same Step/Dir on my RAMPS.

My worry is Z-Wobble.

I haven't really read up on the cause, and since my current Rep-Strap printer doesn't have a moveable bed, it's a non-issue for me atm.

But I'm wondering if the problem would be amplified as a result of having 4 motors.

Edited 2 time(s). Last edit at 11/07/2013 11:28AM by ShadowRam.

Thanks ShadowRam,

* Re: extra pololu's, that's a great solution for getting a working z-axis, but that would not allow for individual movement (for auto bed-leveling), but I imagine you could just run a designated micro-controller for the purpose of bed-leveling (in order to control each stepper individually), but that would also require isolating the paralleled wires (that you mentioned) from the pololu boards.

* Re: z-wobble, thanks for bringing that up. I hadn't really thought about that. But I imagine you would want to implement the same techniques that work when trying to eliminate z-wobble from other printers:
[forums.reprap.org]

Quote
ShadowRam
2) I would just get use some extra pololu's.
Just set up the extra 4 on a bread board and wire them all to the same Step/Dir on my RAMPS.

My worry is Z-Wobble.
I haven't really read up on the cause, and since my current Rep-Strap printer doesn't have a moveable bed, it's a non-issue for me atm.
But I'm wondering if the problem would be amplified as a result of having 4 motors.

With the Cartesio we are now using only 3 TR12x3 spindles, as this has been proven to work better with levelling.
(a lot of debat about this: it is physically imposible to level a bed that is supported at 4 corners)
We still use 1 (NEMA23) motor and have probably the fastes Z movement around. but who cares, unless you are homing

The "problem" is that you have to use a endless belt, and these have a lenght limit.
so be sure to check the max lenght of your belt.
rule of thumb: the higher the pitch the longer the max lenght.

If you are going tu use more motors make sure all cables are equally long, and the stepperdriver(s) are up for the task.

Quote
ShadowRam
Has anyone tried or has examples of a print bed that utilizes 4-stepper motors?

My custom repstrap has a fairly large print area, and while currently I'm only using a small portion of it, with a smaller bed,

I'm planning ahead as to how I'm going to achieve the larger bed.

Size is approximately 600mmx300mm

I was thinking 4 Steppers in each corner, where I could fine tune the leveling of the entire bed via a few step adjustments

Quote
ShadowRam
Has anyone tried or has examples of a print bed that utilizes 4-stepper motors?

My custom repstrap has a fairly large print area, and while currently I'm only using a small portion of it, with a smaller bed,

I'm planning ahead as to how I'm going to achieve the larger bed.

Size is approximately 600mmx300mm

I was thinking 4 Steppers in each corner, where I could fine tune the leveling of the entire bed via a few step adjustments

4-point bed support is a bad idea unless the bed is flexible, which it shouldn't be. With multiple motors, when you power the machine off and on again, the motors will jump to the nearest place that corresponds to the way the motor is energised, which could be up to 2 full steps away from its initial position. Different motors may jump in different directions. The traditional solution for large beds is to use 3 leadscrews driven from a single motor by a belt.

However, there is another solution. Use 3 motors and use a Z probe to level the bed during Z homing by controlling the motors independently. This requires special firmware support, which is on my list for adding to RepRapFirmware, because there are other users who want to try it. A Duet electronics board plus the DueX4 expansion board will provide the necessary hardware support - the combination provides 9 stepper drivers.

If you do go this route, you must design the mechanics to allow for the leadscrew angles changing slightly as the bed plate tilts. For example, you will need something like a ball joint where each leadscrew supports the bed,

Edited 1 time(s). Last edit at 05/23/2016 12:49PM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

For my current printer (1200mm x 1200mm x 1200mm) I use 4 stepper motors to raise the x/y carriage rather then the bed. Here is a video to it
[www.youtube.com]

Even though on the video there is only 1 2ftx2ft plane of glass, I setup 3 more planes of glass which fill up the whole bed and is very even.

Currently I am using a 4 probe setup (with 4 more probes for each side) and I am having no issues. I will see how it will do in the long term, or for taller prints, however as it is now I am having no issues.