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Prusa XL has side filamentsensors and filamentsensors in the extruders. The mechanism of a sensor consist of a metal ball, a 3x3mm neodymium magnet, read by a Hall sensor, and a spring. The force exerted by the spring is sufficient to cause rather substantial resistance in the filament path past the sensor. This makes it difficult to feed soft filaments, like flex or PP, through the standard filament path.

Here follows a just slightly modified version of the mod by @kaaaaaaaaaaaaal in the forum (https://forum.prusa3d.com/forum/original-prusa-xl-tool-changer-user-mods-octoprint-enclosures-nozzles/xl-filament-sensor-mod-for-tpu/). I have copied both text and images in order to have this mod collected in one place. The model contributed in this remix is simply a remix of the standard Prusa XL side filamentsensor with holes for the magnets as described below. Thus, most of the credit should go to Kaaaaaaaaaaaaal.

I bought the magnets for this mod here: https://www.amazon.se/-/en/Brudazon-Magnets-3x3mm-Strongest-Level/dp/B07N52D5NS

Kaaaaaaaaaaaaals mod [with a few notes of my own inside square brackets]:

Extruder filamentsensor

\u201cFor the extruder filament sensor, I took apart the extruder assembly by removing the gear box cover, gears with brass section, and the last plastic insert that helps guide the filament. [This last plastic insert is called the \u201dbase plate\". You can remove all of this after having removed the three screws in the gear box cover. I would suggest printing out the PG-assembly-adapter as described here: https://help.prusa3d.com/guide/how-to-replace-nextruder-heatsink-xl-multi-tool_559633] I then pulled out the filament sensor housing with small needle nose pliers (should come out easily). The ball bearing/magnet and spring should fall out when the housing is tipped over.

[The orientation of the magnet adjacent to the ball now becomes important. If oriented in the wrong way, the magnetic field will cause the Hall sensor and firmware to give inverse result. On my printer, the Prusa magnets had a small dot in one end. This should be oriented towards the ball.] Layout of the magnets to be put into the sensor housing. I had to use a hex key to guide the first magnet to go in the correct way and the small rod to temporarily pin the magnet in place to remove the hex key and place the original magnet back into the housing.

Make sure magnets are repelling each other. the bottom magnet should be captured in the housing so no glue was needed to keep it in place.

Filament sensor housing installed back into the extruder assembly.

Side filamentsensor

On the side mounted filament sensor the new magnet in place of the spring did not allow for proper function of the hall effect sensor so I had to take a different approach. For this sensor I mounted the new magnets on the outside of the housing so that they would attract the original magnets. I used the same 3mm diameter and 3mm long magnets from the extruder sensor change. First step here was to remove the sensor housing [using an Allen key inserted into the middle hole to bend/push the housing away from the 8mm screws] and take out the sensor board assembly, remove the board, and take out the springs. [The springs are most easily removed using a small flat screwdriver which both can be used to move the end of the spring in level with the small opening and to reorient the spring to go out of the opening.]

Springs are removed and the magnets with ball bearings seem to be captured in the print. The board can be screwed back onto the plastic part.\"

Mod continuing with the remixed part

Now, we will make note of which orientation of the new magnets will attract the balls. Then insert the magnets into the modded entry-fs-case and screw everything together. It might be necessary to widen the three holes slightly using a 3mm drill.

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Added holes for three 3x3mm magnets.

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Filamentsensor upgrade for XL

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