I have three off these units that all need to follow a DC motor with a optical encoder attached yes there is a lot you can do with proximity sensors or reed switches but it does not suit my purpose . It is a experiment that I don't fully want to disclose it is not for 3D printing or DTG stuff or cnc machines it is of my own creation and needs too follow a optical encoder obviously the Adifruit motor shield is not good enough or anyone with enough experience to make this work. It is not the end of the world as there are other ways just not what my original vision was but that's life