mmu2s finda selector with retention spring for steel ball

This is a remix of the original mmu2s selector from prusa.

I always had problems with the reliability of the finda sensor in the selector. I first tried the mod with a magnet e.g. https://www.prusaprinters.org/prints/48794-prusa-mmu2-selector-magnet-upgrade-r2 . Since the steel ball is not very magnetic, it wasn't much of an improvement.

A solution like the IR Sensor/lever assembly in the extruder would be ideal but is to big a project for me. So I solved the problem with a simple spring-steel spring. Since I installed the mod I didn't have a single error reading from the finda sensor.

The spring is very simple and can be bend with regular pliers (e.g. the one that came with printer). I used 0.5mm springsteel which I bought on ebay. The pretension can be adjusted by bending the spring more.

I also made the cones at the filament path beginning and end a bit bigger.

Here a small video

The unmodified prusa scad file can be found on github https://github.com/prusa3d/Original-Prusa-i3/tree/MMU2/