Hi everybody! Seems i need to hear a voice of guru/community to be sure that i am doing well and not “reinventing the wheel”… I am designing my first cubic 3D printer with heat-bed which move along Z axis. Seems the most popular solution for such type of printers is CoreXY or H-BOT. I was searching for more variants but all what i find - is solutions with non moving motors. Seems all of them causes reactive torque on the printing head and due type of construction have such CONS:
-frame of printer must be very rigid to compensate torque in opposite directions
-to move along one axis must work motors of both.
-as result not rigid frame, sagging belts, or backlash in motors/gears etc can cause not ideal positioning on sharp corners.
So now the time for my question:
Is it rational to move X-motor with axis to get the better quality by donating speed?
AFAIK belt stretch is not really an issue even for moderately sized CoreXY. I would not put the motor on the moving axis, unless you want to do dual extrusion/separate heads.
The bending and rattling inside the machine caused by accelerating and decelerating of the motor mass will always be more problematic then the belt stretching.
The CoreXY belt path solves the torque issue on the print-head that goes along with the H-bot belt path (for more info on this: http://www.doublejumpelectric.com/projects/core_xy/2014-07-15-core_xy/). Yes both motors must do work in this type of motion style but it’s not really an issue, especially if you use 24V instead of 12V. Plus the print-head usually only moves purely in X or Y when printing perimeters and you usually want to print those slower anyway. How big of a build volume are you trying to get? Backlash is usually only an issue with extremely long belts.
As +Øystein Krog mentioned above the movement style with the build-plate moving in Z and the X motor moving along the Y axis is only really used in IDEX printers now (at least until CoreXYU gets firmware support). The moving X motor was in the old Makerbots, Flashforge Creator, and Sollidoodle printers all of which are now pretty obsolete. Having a stationary X motor significantly lowers moving mass which inherently gives greater quality at the same print speed.
Hm, if you look closely, you will see this is not a corexy design. And it should be.
Hold on, why are you using two Y motors?
@Adam_Steinmark I design it to work with one or optionally two motors on Y-axis (just in case if one will not be enough)
@Adam_Steinmark after what length would you define a belt to be extremely long?
@Thomas_Balu_Walter a good rule of thumb for “long” is over a meter between the drive pulley and load at the worst-case carriage position. When the belt is in a loop and properly preloaded, the shorter leg does the majority of the drive work by tightening slightly to pull or loosening slightly to allow the other leg to pull. So you don’t really care how long the longer leg of the loop is.
Thanks for all replies. Some of them very meaningful. But still unclear one question: What about opposite forces which appearing in printing head due motors opposite rotation. I think this issue reduce torque of both motors and in case of strong motors - loses of torque may be more than impact of inertia force of attached to x-axis motor?
@1111113 the motor forces are always perpendicular to each other, so they never oppose each other. It is the same as when a traditional XY gantry printer moves on a diagonal. Both motors move the load but along different vectors so there is no conflict.
@Ryan_Carlyle Us i understand even different tension of belts can cause problems (especially on circles). Also every pulley can affect print quality. So if you use separate axes - you may not pay attention at light jams if the motor torque is enough to pass it. But if you have some slight jams or backlash in coreXY (especially H-bot) - you will have bad affect on second axis. For example like this:
@1111113 That only happens with H-bot, due to unbalanced belt forces. The CoreXY belt arrangement 100% fixes that problem and does not have any issues.
H-Bot is a pretty terrible gantry design. CoreXY was created to solve the problems with H-Bot.
Taking to account all comments i decide to implement CoreXY method. Thanks for inputs to everybody, it was a very helpful for me ! Special thanks to @Ryan_Carlyle )
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