<p>Wow, Kevin O'Connor (of Klipper) just pointed me to a real CoreXYE design by Vlad Strateniuk called REXY, with video available:</p>
<p><div class="youtube-embed"><div>
                <iframe width="640px" height="395px" src="https://www.youtube.com/embed/TQYYHrxIG90?start=70"></iframe>
            </div></div></p>
<p>There's an <a href="https://github.com/KevinOConnor/klipper/issues/3821" rel="nofollow noreferrer">open Klipper issue</a> about supporting it and apparently Marlin was already adapted to run on it.</p>

CC BY-SA 4.0
2021-05-07T06:08:10.377Z
Very interesting! Doesn't such a system have a limit on extrusion speed? I guess the extruder motor compensates speed of the carriage, so, sometimes it has to run faster than a normal extruder would do. Maybe you could dwell upon such issues in the answer?
0scar
CC BY-SA 4.0
2021-05-07T13:35:24.640Z
@0scar: Possibly. I think you need reduction gearing of some sort because the belts can't handle the torque needed at the extruder hob, and reduction puts a limit on extruder motion, but that mostly affects retraction speed, not extrusion speed, and shouldn't matter; even with 10:1 reduction you're still fine, and 3:1 or 5:1 is probably enough.
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CC BY-SA 4.0
2021-05-07T13:36:54.470Z
There is the matter of needing the *sum* of speeds, but I think if you have 2 E motors like in the REXY, the one going the opposite direction of the XY belt motion (needing added speed) can run at very low current and the one running in the same direction (needing difference of speeds) can run at full current. But that would require dynamically controlling the current, and I'm not sure how fast drivers can switch it. The total speeds probably aren't enough to need this, anyway, though, unless you're trying to do a 3-minute benchy...
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-05-07T14:03:27.000Z
I take it that everyone is forgetting that you need a seamless E belt for this to work at all. The person who posted that video said that they are using normal glue to hold the belt together, but that they are looking for one that is seemless.
user77232
CC BY-SA 4.0
2021-05-07T14:53:27.667Z
there are tons of deign issues, but the result is a super light direct drive, so those can be seen as tradeoffs.
Trish
CC BY-SA 4.0
2021-05-07T15:16:35.777Z
@user77232: Amazon has all kinds of closed-loop GT2 belts for sale for very reasonable prices. I would assume they don't have problematic seams but I'm not sure. And I know some might balk at this, but you can plausibly print working closed-loop belts. I did some experiments with a mystery flex filament a few years ago (3D Solutech brand, not described as "TPU" but "flex PLA") and it seemed workable.
R.. GitHub STOP HELPING ICE
CC BY-SA 4.0
2021-05-07T00:35:36.533Z
2021-05-07T00:35:36.533Z
R.. GitHub STOP HELPING ICE
<p>Thinking about different types of extruder designs, and especially remote direct drive, I wondered if anyone's ever made a cartesian bed slinger printer (Ender 3 style) where a direct drive extruder on top of the X carriage is driven by a stationary E motor at the end of the gantry via a belt. This would of course turn the extruder hob whenever there's motion along the X axis, so the X and E motors would have to be synchronized, with effective extrusion being the difference of the X and E motor motions (thus my allusion to CoreXY in the name). Are there reasons not to do this, aside from needing an over-engineered belt assembly with closed loop belt? It seems like you could get whatever reduction you need just with an appropriate belt pulley, and no need for a gearbox on top of the hotend to get the necessary torque to the extruder hob.</p>
<p>Of course as described this only makes sense for bed slinger printers, since if you have to move the gantry in the Y direction, you have the motor mass moving just like a normal direct drive. Of course it might be extensible to &quot;CoreXYE&quot; with an appropriate belt layout.</p>

CC BY-SA 4.0
2021-05-07T00:24:18.407Z
Prior to our makerspace shutdown, a student mechanical engineer and I had a discussion about this exact topic. He had seen a paper espousing the concept. Unfortunately, it's been more than a year and for my brain, it's more like dog years. I found the concept interesting, but neglected to pursue it. Suffice it to say that it's likely someone has given the idea some consideration.
fred_dot_u
<extruder>
Is "CoreXE" a thing, or is there a reason it's not?
R.. GitHub STOP HELPING ICE
# Is "CoreXE" a thing, or is there a reason it's not?

(Asked by: username_0 on 2021-05-06)

Thinking about different types of extruder designs, and especially remote direct drive, I wondered if anyone's ever made a cartesian bed slinger printer (Ender 3 style) where a direct drive extruder on top of the X carriage is driven by a stationary E motor at the end of the gantry via a belt. This would of course turn the extruder hob whenever there's motion along the X axis, so the X and E motors would have to be synchronized, with effective extrusion being the difference of the X and E motor motions (thus my allusion to CoreXY in the name). Are there reasons not to do this, aside from needing an over-engineered belt assembly with closed loop belt? It seems like you could get whatever reduction you need just with an appropriate belt pulley, and no need for a gearbox on top of the hotend to get the necessary torque to the extruder hob.

Of course as described this only makes sense for bed slinger printers, since if you have to move the gantry in the Y direction, you have the motor mass moving just like a normal direct drive. Of course it might be extensible to "CoreXYE" with an appropriate belt layout.

**Tags:** extruder
> **Comments:**
> **username_1**: Prior to our makerspace shutdown, a student mechanical engineer and I had a discussion about this exact topic. He had seen a paper espousing the concept. Unfortunately, it's been more than a year and for my brain, it's more like dog years. I found the concept interesting, but neglected to pursue it. Suffice it to say that it's likely someone has given the idea some consideration.  

---

## 1 answers

### Answer by username_0 on 2021-05-07. Score: 2

Wow, Kevin O'Connor (of Klipper) just pointed me to a real CoreXYE design by Vlad Strateniuk called REXY, with video available:

There's an [open Klipper issue](https://github.com/KevinOConnor/klipper/issues/3821) about supporting it and apparently Marlin was already adapted to run on it.

> **Comments:**
> **username_2**: Very interesting! Doesn't such a system have a limit on extrusion speed? I guess the extruder motor compensates speed of the carriage, so, sometimes it has to run faster than a normal extruder would do. Maybe you could dwell upon such issues in the answer?  
> **username_0**: @0scar: Possibly. I think you need reduction gearing of some sort because the belts can't handle the torque needed at the extruder hob, and reduction puts a limit on extruder motion, but that mostly affects retraction speed, not extrusion speed, and shouldn't matter; even with 10:1 reduction you're still fine, and 3:1 or 5:1 is probably enough.  
> **username_0**: There is the matter of needing the *sum* of speeds, but I think if you have 2 E motors like in the REXY, the one going the opposite direction of the XY belt motion (needing added speed) can run at very low current and the one running in the same direction (needing difference of speeds) can run at full current. But that would require dynamically controlling the current, and I'm not sure how fast drivers can switch it. The total speeds probably aren't enough to need this, anyway, though, unless you're trying to do a 3-minute benchy...  
> **username_3**: I take it that everyone is forgetting that you need a seamless E belt for this to work at all. The person who posted that video said that they are using normal glue to hold the belt together, but that they are looking for one that is seemless.  
> **username_4**: there are tons of deign issues, but the result is a super light direct drive, so those can be seen as tradeoffs.  
> **username_0**: @user77232: Amazon has all kinds of closed-loop GT2 belts for sale for very reasonable prices. I would assume they don't have problematic seams but I'm not sure. And I know some might balk at this, but you can plausibly print working closed-loop belts. I did some experiments with a mystery flex filament a few years ago (3D Solutech brand, not described as "TPU" but "flex PLA") and it seemed workable.  

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