inclination; force sensors placed in robot's hands and feet to measure contact force with environment; position sensors that indicate the actual position of the robot (from which the velocity can be calculated by derivation); and even speed sensors. Exteroceptive Arrays of tactels can be used to provide data on what has been touched. The Shadow Hand uses an array of 34 tactels arranged beneath its polyurethane skin on each finger tip. Tactile sensors also provide information about forces and torques transferred between the robot and other objects. Vision refers to processing data from any modality which uses the electromagnetic spectrum to produce an image. In humanoid robots it is used to recognize objects and determine their properties. Vision sensors work most similarly to the eyes of human beings. Most humanoid robots use CCD cameras as vision sensors. Sound sensors allow humanoid robots to hear speech and environmental sounds, akin to the ears of the human being. Microphones are usually used for the robots to convey speech. Actuators Actuators are the motors responsible for motion in the robot. Humanoid robots are constructed in such a way that they mimic the human body. They use actuators that perform like muscles and joints, though with a different structure. The actuators of humanoid robots can be either electric, pneumatic, or hydraulic. It is ideal for these actuators to have high power, low mass, and small dimensions. Electric Electric actuators are the most popular types of actuators in humanoid robots. These actuators are smaller in size, and a single electric actuator may not produce enough power for a human-sized joint. Therefore, it is common to use multiple electric actuators for a single joint in a humanoid robot. An example of a humanoid robot using electric actuators is HRP-2. Hydraulic Hydraulic actuators produce higher power than electric actuators and pneumatic actuators, and they have the ability to control the torque they produce better than other types of actuators. However, they can become very bulky in size. One solution to counter the size issue is electro-hydrostatic actuators (EHA). The most popular example of a humanoid robot using hydraulic actuators is the ATLAS robot made by Boston Dynamics. Pneumatic Pneumatic actuators operate on the basis of gas compressibility. As they are inflated, they expand along the axis, and as they deflate, they contract. If one end is fixed, the other will move in a linear trajectory. A popular