I started with a QUBD extruder and printed a few different upgrades for it. The extruder this is based on was reliable and I used it till about a year ago as a direct drive. On my newer printers I changed the design so that instead of a heatsink and fan mounted to a small cooling block on the motor, I made a large heatsink with fan that the barrel screwed into and the motor and mounted on top. I later changed this to a bowden design and this design can still be mounted as both a direct drive and a bowden. The arm has however changed significantly from the original. the biggest change is the bearing mount now requires a 8mm shaft for the bearing about 15mm long. The spring I use is a much larger diameter one and I source it from RC model cars suspension shock absorbers smaller springs can still be used but you may need to add a cutout to the arm for it. the frame mount is to mount it on a 25mm frame ( I use 25mm square tube aluminum frames on my machines) you may need to design your own to suit your requirements. If you do please feel free to send then and I will include it in the files. Pictures attached are; The evolution of the design over time The assembled extruder close up and entire setup. The bearing grove for reference