Bambu Lab - H2D - Extruder Switch Cam

The extruder switching system operates via a switching motor and a transmission mechanism that drives the extruder switching cam. This action causes the left and right driven wheel rods (driven rods) to oscillate. A tension spring attached to the driven rod ensures that one driven wheel is pressed firmly against the drive wheel, enabling filament extrusion whilst the drive wheel rotates. At the same time, the opposite driven wheel remains disengaged, thereby preventing unwanted filament movement.

Further information can be found on Bambu Lab Wiki.