Actually, reading this diagram a bit more, it looks like we’d just have to get the distances between each belt measurement point, where they come out of the spools on the maslow, and then use half the x/y distances between those 4 and insert those values in the relevant parenthesis for each calc.
For example:
D1 = sqrt( sq( Xoffset + x - 0.5( sledX ) ) + sq( YMS - Yoffset - Y + 0.5( sledY ) ) + sq( Zoffset ) )
Where sledX and sledY are the distances between the ‘start’ points of each belt on the sled on the X and Y axes, respectively.
I would expect that, if it’s a good calc to get the right belt lengths to put the center of the unit at the desired XY, it should also have each of the belts at their minimum length to achieve that and maintain orientation. From watching the Maslow 4, it appears that it is only rotating because it is both free to do so and because of friction between the sled and workpiece.