CoreXY design flaw spotted, EdgeXY concept fixes it, comments and review of analysis appreciated (3 replies)

hi, i was made aware of a design concept called EdgeXY just recently, and so did a design analysis comparing it to CoreXY:

[forums.reprap.org]

the conclusion: CoreXY has a design flaw, which only surfaces under very specific (combined) conditions: (a) high acceleration, (b) carriage is off-centre on the X-Gantry (left or right, but the further away from centre the greater the distortion) and (c) movement (with high acceleration) is in the Y-direction.

if we were to work out a formula for the amount of distortion it would be:

* let width of printer be called X
* let the position of the carriage on the X-gantry be Px
* let center point of X-gantry be Cx, equal to X/2
* let acceleration in Y direction be Ya
* let c be an arbitrary constant
* let the function absolute(X) be equal to X if X > 0 otherwise -X

then the amount of distortion would be:

* c times absolute(Px-Cx) times Ya

the design flaw stems from the fact that the X-Gantry is free to rotate, with only the mechanical strength of the rails/rods and the attachment of the X-Gantry to those rails/rods being the sole method of stopping any such potential rotation.

in the message referenced above i carry out an analysis which shows that the Edge-XY concept does *not* suffer from this critical flaw.

can anyone spot a mistake in either the Edge-XY analysis *or* the CoreXY analysis?