Upgraded replacement elevator motor shaft for JOYIN Marble Run

My kids broke the shaft that came with their JOYIN Marble Run elevator. I found kennyxxl82's excellent 1:1 model (https://www.thingiverse.com/thing:6954986) and printed a replacement. It worked well at first but the basic PLA I used as too flimsy and, with minimal resistance, the U-shaped interface to the motor output shaft would flex allowing the motor shaft to spin within the 3D printed extension shaft.

I modified the design to convert the U-shaped interface to a full box increasing the strength. I also added a half-sphere to the smaller disc to reduce the necessary supports when printing.