Anyone know why CoreXY is so popular over HBot style? I’m trying to find reasons not to design an HBot. The belt path looks cleaner… my best guess would be a better balance of torque across the horizontal axis, but I could be wrong.
AFIK:
CoreXY designs require more motion parts (pulleys, belt, idlers, etc.), but avoid racking because the frame forces are precisely along the X and Y dimensions. They are also generally somewhat taller assemblies because the belts run at different levels.
HBot designs apply forces at an angle, which can cause racking in lightly-built machines, but require fewer motion parts, and take up less Z height because the belts are at (approximately) the same level.
I’d guess the popularity of CoreXY is largely that most printers are shockingly lightly built as a matter of cost and speed, so designers gravitate toward a couple extra (light,cheap) pulleys over linear rails or the like to handle the off-center forces.
I’ve linked a reprap forum thread where some folks were discussing the technical merits, it’s a little argumentative and has some …questionable… assertions, but makes interesting reading.
https://reprap.org/forum/read.php?397,767054
CoreXY makes the XY motors stationary, lightening the gantry which increases the gantry’s max acceleration.
HBot has the axis motor on the gantry, which is extra intertia to overcome.
HBot drive forces are unbalanced and try to rack the gantry out of square. The linear hardware / Y-carriages have to be very, very stiff to avoid acceleration-dependent-skew errors in prints. EG circles come out deformed.
CoreXY is exactly like HBot in every meaningful way except it inverts part of the belt routing so drive forces are balanced. Thus belt tension inherently keeps CoreXY gantries square, without relying on moment loading the linear hardware.
I have never seen a single particularly good reason to build an HBot instead of CoreXY. Lots of mediocre reasons, but nothing impactful enough to overcome the inherent racking issue.
@Cruz_Monrreal_Mr_Cru that’s not HBot. You’re probably thinking of a regular Cartesian XY bridge gantry.
@Ryan_Carlyle Aw crud, my bad.
@Griffin_Paquette To add on to @Ryan_Carlyle 's explanation, see this reference: http://www.doublejumpelectric.com/projects/core_xy/2014-07-15-core_xy/
@Cruz_Monrreal_Mr_Cru that makes complete sense! No reason to have racking for a little less designing.
Thanks guys! This is quite interesting stuff!
I find the coreXY much smoother when printing and you can print faster and not lose detail. I’ll try post a vid of a 130mm/s that still maintains details with 90deg changes in direction.
@Paul_Eberhart I have two CoreXY printers (one unfinished) that route the belts in single plane. Put a twist in the belts in front, so they cross w/o issue. As a result the assembly in of minimal height.
@Preston_Bannister Neat, I didn’t know that was an option. Looking at some examples, seems like you need a tiny bit of extra XY area on the gantry to get clearance around the pulleys, but that’s a nice topology.
@Paul_Eberhart No extra clearance needed. On the first build, I put a spacer between the belts. For this, just let the belts touch (to see how/if that would work). The force between the belts is tiny, and after hundreds of hours of printing … this is just not an issue.
Totally agree that belt rubbing is a non-issue. I’ve tried comparing crossed-rubbing and separate-plane belt routes on the same printer, and never noticed the slightest difference.
@Preston_Bannister do you find they rub to much? I have 2 of the X5S and have modified both. I’m wondering about printing at 100mm/s + speeds.