Been doing a lot of thinking, drawing, sketching and calculating and a potential problem about having a heavy dual direct drive on a ultimaker style gantry, even a beefed up one is unsuitable and will potentially have problems such as deflection, bad vibration, complexity, etc.
Due to the geometry of the cross section of a linear shaft and the small diameter possible there isn’t much resistance to deflection. Since we know that the force equates to the mass times the acceleration and that the moment of inertia for the shaft is relatively low, as the printer is in motion the linear shafts could bow back and forward due to the high mass of the gantry.
The cartesian printer is expected to work perfectly from the get go, the uncertainty of this design, mean’s i will have to reiterate and explore new motion design. I will look at the most simple and reliable 3d printers available and work on those simple designs. This is a step back, but a necessary one.