I have started on making my third humanoid robot. This one is modeled after the EZ-Robot JD Humanoid. The issue with the larger humanoids is that their center of gravity is way too high. There is a two degree tolerance in each servo and that is amplified by the distance from the servo's. So in a humanoid that is over 16" tall the two degrees can amount to falling over frontwards or falling over backwards. That makes it really hard to write software for walking.
One solution is to make the robot shorter and to make the distance from each servo shorter. In the following picture there is a servo for the EZ_Robot on the left, for the Hadron Robot in the middle, and for the mechanical robot sold on eBay on hte right. The EZ-Robot assembly is so short that the ears need to be cut off the one end of the servo for it to work. The Hadron robot on the other hand is not much smaller than the mechanical version, it also is not quite square.