I consistently have issues with this printer causing false positives from the run-out sensor, pausing mid-print when it wasn’t needed. Dangling the run-out sensor right on top of the direct drive is not good for me, I know a lot of people do this and get away with it, but it doesn’t work for me. At first I thought it was the constant retractions, but further experimenting showed it was the sudden head movements that was activating the switch. 

My next step was to figure out how to mount it between the spool and the printer, allowing full range of movement but without the constant jerking. My design solves this problem and also keeps the filament spooling from the center of the spool, not allowing it to wind over the edge and cause jamming.

The bowden tube sets a minimum slack between the run-out switch and the extruder. This helps to prevent binding when the extruder moves from close to far away at right angles.