Belt driven Z axis

I understand that belts may not be as good as screws for lifting a heavy heated bed with a weight of plastic.

The Voron printers 2.4 and Switch Wire use belts to lift the X axis or motion carage.
However some of the things I have read suggested there would not be enough resolution (Z steps per mm) unless a large pulley is included.

Assuming a normal 1.9° stepper that's 200 steps per rotation if you set up microsteping for example 32 microsteps 200x32 micro steps.

I haven't measured a pulley but if I assume a 30mm circumference then the resolution should be

...........................30/(200×32) mm ~ 0.005mm

Surly that's good enough, 0.1mm is the thinnest layer I would ever attempt.

Is this correct or have I misunderstood something?

Atb aamcle

... it's lack of "stiffness" too - the magnetic field inbetween the steps (where microstepping is performed) ist not very strong, so the movement will result in "wavy" positioning with "compressed" steps between the fullstep positons and then a "jump" to the next fullstep ...

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Viktor
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Ahh, I didn't know that so that's why a big wheel is often included it's aim would be to use full steps!


Thanks aamcle

... to avoid this "wavy" movement I'm using "overpowered" steppers (=much "stiffer" microsteps) and/or gearing ...

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Viktor
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Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

Do you mean longer
Nema17s or have you gone to 23s?

I have just had a look at the SwitchWire Bom there's nothing specialzbout the steppers and no particularly large wheel.

How have they managed to resolve the issue?

Aamcle

Edited 1 time(s). Last edit at 10/30/2022 08:05AM by aamcle.

... NEMA23 ... but mostly for other applications than 3D-printing too ...

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Viktor
--------
Aufruf zum Projekt "Müll-freie Meere" - [reprap.org] -- Deutsche Facebook-Gruppe - [www.facebook.com]

Call for the project "garbage-free seas" - [reprap.org]

OK thanks.

My corexy machine, UMMD, uses a belt lifted Z axis. It has a NEMA-23 motor with a 30:1 worm gear reducer and it works perfectly. A full step of the motor moves the 3.5 kg bed 20 um. The bed doesn't move when the power is cut (thanks to the worm gearbox), so it is possible to resume prints. I have stacked 4 kg on the bed to do the belt stretch testing and it had no problem lifting it, even though I drive the motor at about half its rated current. I use 16:1 ustepping to keep noise down, so the maximum speed of the Z axis is about 15 mm/sec.

The belts stretch a little, and the total stretch depends on both the bed position and the weight of the print on the bed, but it's not enough to matter. I used only two belts to do the lifting. Using a third belt or even a fourth (if you have a really big bed) would result in even less stretch.

The cost of the worm gear drive unit is about the same as a motor with a solenoid operated brake, which you might need in a machine with a screw driven Z axis, or a simple belt driven Z axis. Belts are a lot cheaper than screws, and can be arbitrarily long, in case you want to make a tall printer. The worm gear drive unit has enough grunt to lift a large, heavy bed, so you don't need to use multiple motors. Using a single motor can eliminate the need for any form of autoleveling, which simplifies things considerably, and increases reliability.

The drivers apply current to the motor that can vary a bit from one microstep to another. That means the amount of rotation you get- i.e. the rotor position- can vary a bit from one ustep to another- i.e. it won't necessarily move 1/16 x 1.8 degrees at each ustep . However, at the same microstep value (say the 4th or 5th microstep), the same current will be applied so you should get the same rotation from the last full step. That is why print layers are generally recommended to be multiples of the full step distance. You'll always end up with the same current (and rotation from the last full step position) because your layers will always be located at the same ustep position. For example, let's say your printer has 20 um full-step resolution in the Z axis. You home the machine and Z ends up 6 usteps (it could be any between 0 and 15) away from a full step. Now you print in 200 um layers. That's 10 full steps. Every time Z moves to the next layer, it is going to land at that 6th ustep away from a full step position. You will get consistent positioning from layer to layer and your print's Z axis will be beautiful.

Driving the Z motor with full steps is OK, but it will be very noisy when you slew the Z axis when homing after a print.

Edited 2 time(s). Last edit at 11/01/2022 08:31AM by the_digital_dentist.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]