Stepper w/Belt Drive in Z-Axis, Possible?

I haven't seen anyone doing a Z-Axis stepper driven belt drive. The obvious answer is that the steppers won't hold the torque when not charged, but has anyone come up with a solution around this, either through programming or a counterweight, or done this in some other way that I have yet to think of?

The Printxel uses a belt for Z I think as does the UP.
The bigger issue is resolution, the screw provides much finer resolution than a belt.
A single full step on a 10 tooth XL pulley is about 0.01in or 0.254mm, I'm not sure I'd trust steppers to hold at half or finer microsteps accurately.
You could gear that down, or find smaller drive gears.
I don't know what the Printxel or UP do for this.

The "doubling resolution" hack someone described for X/Y axis a while ago might help.

From memory, it just use a double length of belt and a doubled belt path like this :

usual belt path :

 __________
O__________O

double pulley path (the inner 2 pulleys are on the carriage and moving) :

 __________
O___    ___O
 ___O  O___
O__________O

Note I'm quite not sure of myself on that description, someone will correct me if needed.

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Most of my technical comments should be correct, but is THIS one ?
Anyway, as a rule of thumb, always double check what people write.

The steps per mm on the Printxel non-double pulley Z axis are 70 with 16 microsteps. So 4.375 steps per mm jives pretty well with the 0.254mm mentioned above. So on paper it might sound borderline, but in practice I have printed down to 50 microns with good layer alignment. If anything some of the other low cost components and design decisions on the Printxel are the weak link when it comes to ultimate print quality. In my opinion a belt drive Z really is about cost savings while still attaining decent respectable quality. I've not found a leadscrew solution for anywhere near the cost.

well then you guys have to consider that your steppers are truly stepping really evenly at1/16 ... as i have found (nophead has alot of experience on this) ... i have done trials with 2 drivers (a4988/4983) .... seems that if the drive current setting (including the R sense) is not build to fit the stepper, the motor will not step 1/16 in equal steps.

Edited 1 time(s). Last edit at 01/13/2013 03:44AM by redreprap.

im going to try and use 400step/rev steppers on a direct Z-drive. but using 4 steppers. 1 each corner

this is what i tried currently
[3roomlabs.blogspot.sg]

I am using GT2 belts and pulleys on my Z axis that has 10 inches of vertical travel

No problems so far

I have the Probotix drivers set up for 16X and the motors are 200 steps - 1.8 degree

One single Nema17 is driving two drive shafts that have two belts and four GT2 20 tooth pulleys

The weight that this motor has to lift is not huge
My X axis and A axis are fairly light

I have set up the Z axis motor in Mach3 to handle this situation

[forums.reprap.org]

[www.el34world.com]

Edited 1 time(s). Last edit at 04/01/2013 05:55PM by EL34.

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