Robust Pen Holder for Drawing Robot

This is a more robust pen holder for an Arduino drawing robot, designed to be printable in an upright position without supports (so the layer orientation will result in a stronger print). Previously I was using this design, which worked well for a while:
https://www.thingiverse.com/thing:2058866
Unfortunately, after a while, the pen holder snapped as shown in the picture (perhaps due to insufficient fill, poor layer adhesion or rough handling), hence this new design which I hope will be a bit