Is it really possible to build a rotary encoder out of a flattened tin can and a couple of photodetectors? Sure it’s possible, but what kind of resolution are you going to get from such a contraption?

[Erich] is the middle of building a new competition sumo bot for 2018. He’s trying to make this one as open and low-cost as humanly possible. So far it’s going pretty well, and the quest to make DIY ...