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Zero Gravity Extruder Direct Drive by Gudo & Neotko

by Neotko May 27, 2017
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That's really overengineered xD

I'm wondering, what is the real benefit of the square bar compare to let's say keyed shaft. They are much easier to source, you can use regular ball bearings and linear bearings (bushings) and proper key will make sure rotation is transferred accurately.
Am I missing something here??

Dunno man, pico the step files and reuse what you want and make your idea. A proper answer would come from Gudo but very sadly he has pass away, so I wouldn’t expect any updates for this. Sorry to be blunt but was a great friend and I’m not up to much talk about this.

I'm sorry for your loss.

Been thinking about your question, and indeed it was one of the many we had at the beginning (you just did catch me on a bad day, but I'm sure he would have wanted to keep helping everyone to make their systems and evolve this one if possible, he didn't stop making stuff until well...)

So, the issue with the linear rains that you say maintly is a) Price and most importantly, the length. The longest I could find year+++ ago was 300-350mm from Misumi (also at a very heavy price). To get a full diagonal from a umo/um2 area you need 370mm minimum, so that was one of the problems. Also the 4mm shaft it's super inexpensive, and on the Gudo CoreXY system the Z problem disappears completely, but I need to gather streght to start packing Gudo files to upload them since well, you know.

If you wanna see more about how this ZGE evolved on the GudoCoreXY search for #gudocorexy on twitter, I and others posted some about it. Ofc the step files and all that are on the hand of me and other user. Ofc the problem is to make a manual etcetc specially since Gudo is not around anymore :(

But back to topic, I been using the ZGE long before this post was made and up to today keeps deliverying great prints, good extrusion torque and lightweight head speed, so I'm just very happy, until I remember ofc... Anyhow, cheers!

If you wanna see Gudo comments on others ideas, he did left a lot of value info on http://www.3dprintingforum.us/viewtopic.php?t=510

If you were to use a hollow shaft stepper, could you flip the square rod so that it slides at the stepper motor end and is fixed at the encoder? This would take all the weight of the sliding assembly (bearings, nuts etc) and put it at the stepper end. Also the bar overhang would then be out the back of the stepper rather than over the print head?

Edit: On second thought that would mean the print head ends up pushing the bar around so would only be useful if you were to use a lightweight square bar.. have seen some 10x10 CF rods. I wonder if they would be rigid enough.

I didn't really read through the description and comments, so excuse if me if it has been already addressed.
Generally I like the design very much, I've been thinking about something similar in theory for a long time. I see that You've gone to great length to make the torque transfer smoother on the extruder side.
Have you ever considered or try to deliver the power through two rods rotating in opposing directions? That would hopefully eliminate the effect that applying torque tries to twist the whole extruder assembly. I guess that it could improve the handling of retractions.
It's unique and interesting btw.


Gudo designed now a Corexy. With this new change to remove the wooble smooth rods the Z issue isn’t an issue anymore.

Check the status on https://twitter.com/neotko/status/923135097741697024 chain tweets. So far I have it working for a month non stop. No issues and the orint quality is just amazing after I did the correct belt calibration as gudo suggested.

Now at 3000 acceleration and 20 jerk, I get zero ringing (or close to zero) compared to the um2 gantry system. So little weight and with rails there’s no Z wooble. Also check the losts about the Z skis I designed. All that removes the last bit of wooble of the system.

About using 2, think that it would not matter as long the force would be on the same direction the issue will exist. The flexible addon does help a lot for um2 gantry system. But moving all to rails corexy is just amazing the jump on quality to prit faster with good quality

Don't quite get what special use case this is supposed to be for. If you don't want any weight on the print head, just use a bidden bowden extruder. Otherwise this just looks super over complicated and more of a "solution looking for a problem" sort of thing. Looks cool though.

bowden cant extrudes as precisely as direct. and result bad quality prints (regardless your motion system)

Basically is to use full size stepper motors on a directdrive without the problem of adding 250grms (bondtech for example) on the top of the printhead.

Not clear how it deals with gravity (joke)
Actually the extruder weight is only increased with at least half of the rode (actually more since the free end of the rod continues longer behind the head) and additional plastic connectors weight, since it is just secured on the top of the original head.
In addition, for high speed printing the important counter factor is not only weight itself, but also mass of the head and the moving rods. For higher quality print at high speed the head must stop where the controller think it has to stop. But due to inertia of mass the head continue its movement a bit further. This lowers precision adn quality of the print. So the construction with higher overall mass head has higher inertia and lower quality of print.
I would prefer use of Bowden (remote) drive for plastic. Just choose teflon tube of 2mm internal diameter for 1.75mm plastic.

Indeed, there's inertia, most of the weight is translated, specially if you use the bondtech motor that weights more than the one I use, to the motor. The inertia ofc is there.

On our test we had, on the first beta, not this current design, quite a few Z banding that at first wasn't easy to see, but was there, that's why the current design leaves as much room for the rod to not hit the extruder, and the extrusion force is translated to the extruder by the slider, this do remove much of the imprecision of a 4x4mm square rod (because we where not able to source anything longer than 350mm rectified steel key). I know that some users on the UM forum have found rectified square rods, but still don't know where they buy them from.

But back to your question. The UM gantry is quite 'weak' since is made for bowden, as we explain on the loooong text. So, indeed increasing the mass, even 50-60grms on the head, does affect the quality, but the direct drive extrusion also increases it, allowing very small details, and a lot of precision compared to bowden. For example I can do just tons of retractions without any issue, tangle, clog, using recreus filaflex or ninjatek ninjaflex, that was one of the two main objectives when Gudo started doing this extruder, to be able to print flexibles without any worry.

Ofc, we found out on the months of testing that 2.85 flexible is much easier to print than 1.75, just because you are pushing a thicker material and you can actually generated more positive extrusion force, but I use 1.75 on my 3 machines with this zge, and with some clever settings I can do 60mm/s semiflex at 0.18 layer at 245C with very good print quality.

Also, to dampen the gantry system from the sudden moves from the extruder being connected to the top of the printhead, we are using now a beta version with flexible material inside the bearing holder, that was my idea (I like crazy ideas) and the result is a big improvement on the Z errors due extrusion happening on top of the printhead.

For example
Left is without the dampening on the printehad, and right is with it. Is a macro shoot printing benchy with blue to show as many errors as possible.

Check the hashtag #gudozge on twitter for more shots.