I always like to see what is going on with my printers. Sometimes I wonder what movement the extruder motor is making (extruding, retracting, slow, fast, etc.), which is not always so visible on the Prusa i3 MK2 / MK2S / MK2.5 / MK3.

Hence I have designed an indicator that you can magnetically snap onto the axis of the NEMA extruder stepper motor. Just print the design, glue a magnet with some super glue onto it (let the glue dry...) and snap it on the motor (make sure to glue the magnet to the 'raised' side). These print in only a few minutes.

Just for the fun I designed a "Dutch Windmill" version. For the purist: unfortunately the extruder motor rotates clockwise when extruding while original Dutch windmills turn counter clockwise :-). Also added a version with smileys. Pls feel free to make your own design and do not forget to post a "made one"!

I have uploaded now 6 versions:

• Indicator version for a 8x3mm Magnet
• Windmill version for a 8x3mm Magnet
• Smiley version for a 8x3mm Magnet
• Lightning version for a 8x3mm Magnet
• Indicator version for a 6x3mm Magnet**
• "Turbine" version for a 8x3mm Magnet (https://www.thingiverse.com/thing:2802136)

** note that the 6 mm magnet version is not a success for me (it rotates, but slips too much). I leave the design available since maybe it works for somebody else, but my recommendation is to use the versions with 8x3mm magnets.

Mikolas Zuza from Prusa Research has also posted an article about this indicator / visualizer on Prusa's website: https://www.prusaprinters.org/visualize-extruder-motor-movements/

Edit 06-02-2018: In the comments below, Insanity682 pointed rightfully out that he posted already a magnetic attachable extruder indicator before me - of which I was not aware (https://www.thingiverse.com/thing:2285254), so credits to him. Following this notification I could find that Tinkerer did something similar in 2013 already https://www.thingiverse.com/thing:119000), so kudos to him / her as well.
Maybe there are even more! Anyway, credits to whomever deserves it, I just hope people like it. ☺

https://youtu.be/YSM4HN9qsq4
https://youtu.be/cpXcXe8jRyE
https://youtu.be/R37Sh5CsHQE

Neodymium Magnets are easy to find, for example here:
http://www.ebay.nl/itm/Hot-Sales-N52-Super-Strong-Cylinder-Disc-Magnets-8-x-3mm-Rare-Earth-Neodymium/263071072275?ssPageName=STRK%3AMEBIDX%3AIT&var=562071935207&_trksid=p2057872.m2749.l2649

Update 13-01-2019:
Obviously you can also attach them to the Prusa MMU2 stepper motors ☺