How is it done without any sensors…?
Careful choreographing of movements, wide feet, and an assumption that the surface will be firm, flat, and even.
My 6-DOF biped with no sensor feedback at all can walk, balance, kick, and dance, and as long as the movements aren’t too abrupt, falling over isn’t an issue. Adding axes adds complexity, but doesn’t change the basic laws of motion - as long as the CG is centered over the foot, and the surface is reasonably similar to the conditions under which the movements are programmed, falling over isn’t an issue.
You can even make fairly quick moves, so long as they’re balanced out, and you don’t throw the combined force/moment vectors outside of the footprint at any given time.
Can I add sensors to the nova? It would be tough to mount…