Physical humanoids often require the ability to main-
tain upright balance while performing various tasks involv-
ing locomotion and environmental interaction. Such balance
requirements have been difficult to maintain with traditional
approaches to articulated motion control. We claim that these
difficulties are significantly due the use of parent-space in stan-
dard proportional-derivative (PD) servoing, typically requiring
highly sophisticated decision making policies to function while
maintaining balance. Using inspiration from inverted pendulum
robots, we address humanoid balance control through a world-
space servoing model. Our model retains the same basic form
as the PD-servo, but uses inertial/accelerometer measurements
rather potentiometer-like sensing. Our humanoids are able to
functionally balance, locomote, and recover without sophisti-
cated decision making. We demonstrate the efficacy of our
approach through simulation experiments involving locomotion,
user interaction, ballistic motion, uneven terrain, and dramatic
disturbances.