Walking robots is a difficult study.Robots can walk on two legs,Recent robots can not move on a surface that is not smooth.
The methods that have been applied to this study are:
Zero Moment Point Technique (ZMP Technique)
This algorithm is used in Asimo which is a honda product. The computer of the robot tried to keep the total gravity acceleration and deceleration forces of walking (called inertial forces), these inertial forces are opposed by the force of the floor(reaction force), the floor force pushed back on the foot of the robot.
Many robots that are build during 1980’s(by Marc Raibert) at MIT Leg Laboratory, used daynamic walking. A robot that have one leg and a foot can stay in a up-right position by using the hopping technique (like a person on a stay on a stick). This algorithm is then enhanced to be used by two and four legs. You can see the full set of these robots at the MIT Leg robotics page.
This technique is more effective than the ZMP movement technique, because it can constantly keep track the motion of the robot,place and move the feet of the robot with stability. This algorithm is used by by the Dexter Robot (by Anybot), which is very stable in movement but it can also jump.
This approach defined the use of the momentum of the limbs or the swinging for effective and greater efficieny.This techique approves that a robot can walk down a gentle slope, It proves that a robot can move on a gentle slope, using no power, but using only the force of ther gravity. By using this mechanism a robot only needs a very small amount of the power (motor power generation) to walk on a smooth surface an a little power to walk or climb on a hill. This technique makes robots more(ten times) efficient than the ZMP walker techiques like used in asimo.