The biggest problem is that we still don&#x27;t understand the principles of walking, locomotion, and manipulation. Biology doesn&#x27;t come with any documentation.<p>This is much more than the problem of not having good sensors, not having powerful enough actuators, or solving models. Without understanding the fundamental principles we may not even get the hardware right. Recall early attempts at heavier than air flight that attempted to copy and scale up a bird rather than understand the principles behind how wings worked.