Ok so I have been testing out the dual motor design to find the points of failure. I use 8 pounds pulling from the end until the arm snapped about a inch from the end. Inspecting it further I can see this is for two reasons. One , because it is the greatest point of stress from a leverage position. Second, the plastic is also the thinnest here out of the entire arm design, which leads me to think I might need a bit of design modification to strengthen this area. I could do this by moving the vents a couple of mm away from the edges to thicken the side walls. Also I may add a side edge lip along the bottom.