I've been wanting to install a retrofit thumb control knob for needle positioning on one of my machines ever since I saw it on that new Adler 969. My Tacsew T1563 made a good candidate to try a few things out, and it actually works! The entire project of installing an Arduino controlled high-torque precision step motor drive is rather complex and I'll post more details later. This video is just about how the thumb control knob works: