Here is a minimally actuated bipedal walking robot that features 3D passive dynamic walking. It can start, stop, and turn with a single actuator per leg. It has 3D printed components. It comes with a passive hip joint, 2 leg extension motors and a 7.2v LiPo battery.
This video shows this quasi passive biped robot in action.
[Credit: Sharfin Islam, Kamal Carter, Justin Yim, James Kyle, Sarah Bergbreiter, and Aaron M. Johnson]