Jonathan Hurst, the inventor of the ATRIAS robot, has argued that we have the actuators necessary and that efficiency solves some of the problems with batteries

Jonathan Hurst, the inventor of the ATRIAS robot, has argued that we have the actuators necessary and that efficiency solves some of the problems with batteries[0]. A brushless motor hooked up to a big reduction gearbox can have a pretty high torque density. If we design our robots to be light and design them such that they don't throw away energy with every step, then they can go further with current batteries. [0]http://tedxtalks.ted.com/video/Walking-and-Running-Bio-Inspire http://tedxtalks.ted.com/video/Walking-and-Running-Bio-Inspi...