What are the benefits of the CoreXY design over the basic i3 style machines?
The core XY design is a lot more rigid and because the carriage does both the X and Y axis it reduces vibration from the y axis movement as the bed traveling on Prusa designs carries a lot of momentum.
X and Y move fast with lots of cycles, so putting a heavy heatbed with thick heater wires on X or Y is a perhaps non-optimal design decision from a print quality and reliability standpoint. (The i3 style reduces part count and printer cost, which are a different set of design criteria.) A Z bed is less mass slinging around and a thousand times less flex cycling on heatbed wiring.
CoreXY belt drivetrains have an inherent 1:sqrt(2) pulley reduction, which is loosely equivalent to using ~11 tooth pulleys instead of 16 tooth pulleys in a Cartesian printer, so you get finer resolution and stiffer torque response. (At the cost of some top speed on diagonal moves.)
Main downside to CoreXY is having the XY mass move around the top of the printer, so you need a more rigid and higher parts-count frame to prevent shaking.
Thanks for the info guys.
I generally prefer any XY gantry design with the Z bed moving up and down (like Ultimaker, CoreXY, or H-bot) if only because moving the bed/part around so much doesn’t scale and makes the part more prone to detachment. Also, time lapses look better (although that is minor and capturing on z change only solves that problem). They also (generally) can print much faster.
I didn’t see mentioned before, but the sliding bed induces part cooling too. For some materials, this is a good thing, for other materials it’s a bad thing. Generally, the higher the temperature the material, the worse it is for the print. And with nylon, the mix of strength properties are known to be different based on part orientation while printing, aligned to the X or to the Y, because of this cooling.