On Tue, Jul 25, 2017 at 10:32 AM, Luke Kenneth Casson Leighton < lkcl@lkcl.net> wrote:
fortunately someone posted a few days ago that they have a concept which they've named "Edge-XY"
Actually, they called it EtchXY -- probably in reference to the etch-a-sketch toy.
similar to CoreXY except the single
X-Gantry (the horizontal bar of an "H") is replaced with *dual* X/Y (cross) rods. now, what's particularly fascinating about Edge-XY is that an important and previously under-appreciated design flaw of CoreXY is completely sorted!
I'm not convinced it's so much better -- think you've overlooked something in your analysis. (I'm going to register and post a reply in that reprap forum thread.)
But even if I'm wrong about the rigidity... why bother? The thing that made CoreXY special is the combination of non-moving motors with a simple (thus cheap and lightweight) gantry. Once you've committed to the more complex (thus expensive/heavy) dual-gantry setup, as seen in both your Riki200 design and Etch-XY, I don't see any benefit to be had from long timing belts wrapping around a half-dozen pulleys; there's a much simpler way to drive each axis independently with non-moving motors.
For the X-axis, you put two shafts parallel to the Y-axis, at the left and right sides. They each have two timing belt pulleys (at the top/bottom ends), supporting one loop of timing belt to drive each green block. One shaft is coupled to the motor, the other is an idler.
For the Y-axis, exactly the same thing, rotated 90 degrees.
Or perhaps you've considered this and aren't doing it because of construction details. Etch-XY has 8 short shafts (idlers on the fixed chassis -- not counting the motors or idlers on the moving gantries), all with parallel axes (Z-axis), while the simple solution has 4 long shafts in pairs (X-axis and Y-axis) -- it seems simpler and easier to me, but then I'm a machinist by trade, so I'm not used to thinking in the constraints of 3d-printed and/or laser-cut construction...
Benson Mitchell