Many humanoid robots exist today, however they are all still at a research level and cannot be really used in everyday tasks yet. Most of these robots are meant to serve humans, and so to work safely in close contact with humans. This motivated many researchers to focus their work on safe humanrobot interactions, including development of compliant actuators. Different from rigid actuators, they have elastic elements which can absorb shocks and be possibly advantageous from the energy consumption point of view. One well known compliant actuator is the Series Elastic Actuator (SEA), which introduces a spring in the actuator. In the iCub robot built by the Istituto Italiano di Tecnologia (IIT) a customized version of these actuators was introduced in the knee and ankle joints in a new version of the legs, replacing the previous rigid actuators.