Rocking Team

Walking Robots

iCub robot, designed by the RobotCub Consortium

This is some details about walking robots.Walking is a difficult and dynamic problem to solve. Several robots have been made which can walk reliably on two legs, however none have yet been made which are as robust as a human. Typically, these robots can walk well on flat floors, and can occasionally walk up stairs. None can walk over rocky, uneven terrain. Some of the methods which have been tried are:

• ZMP Technique: The Zero Moment Point (ZMP) is the algorithm used by robots such as Honda’s ASIMO. The robot’s onboard computer tries to keep the total inertial forces (the combination of earth’s gravity and the acceleration and deceleration of walking), exactly opposed by the floor reaction force (the force of the floor pushing back on the robot’s foot). In this way, the two forces cancel out, leaving no moment (force causing the robot to rotate and fall over). However, this is not exactly how a human walks, and the difference is quite apparent to human observers, some of whom have pointed out that ASIMO walks as if it needs the lavatory. ASIMO’s walking algorithm is not static, and some dynamic balancing is used (See below). However, it still requires a smooth surface to walk on.
• Hopping: Several robots, built in the 1980s by Marc Raibert at the MIT Leg Laboratory, successfully demonstrated very dynamic walking. Initially, a robot with only one leg, and a very small foot, could stay upright simply by hopping. The movement is the same as that of a person on a pogo stick. As the robot falls to one side, it would jump slightly in that direction, in order to catch itself. Soon, the algorithm was generalised to two and four legs. A bipedal robot was demonstrated running and even performing somersaults. A quadruped was also demonstrated which could trot, run, pace and bound. For a full list of these robots, see the MIT Leg Lab Robots page.
• Dynamic Balancing: A more advanced way for a robot to walk is by using a dynamic balancing algorithm, which is potentially more robust than the Zero Moment Point technique, as it constantly monitors the robot’s motion, and places the feet in order to maintain stability. This technique was recently demonstrated by Anybots’ Dexter Robot, which is so stable, it can even jump.
• Passive Dynamics: Perhaps the most promising approach utilises passive dynamics where the momentum of swinging limbs is used for greater efficiency. It has been shown that totally unpowered humanoid mechanisms can walk down a gentle slope, using only gravity to propel themselves. Using this technique, a robot need only supply a small amount of motor power to walk along a flat surface or a little more to walk up a hill. This technique promises to make walking robots at least ten times more efficient than ZMP walkers, like ASIMO.

Other methods of locomotion

RQ-4 Global Hawk Unmanned Aerial Vehicle

• Flying: A modern passenger airliner is essentially a flying robot, with two humans to manage it. The autopilot can control the plane for each stage of the journey, including takeoff, normal flight and even landing. Other flying robots are uninhabited, and are known as Unmanned Aerial Vehicles (UAVs). They can be smaller and lighter without a human pilot onboard, and fly into dangerous territory for military surveillance missions. Some can even fire on targets under command. UAVs are also being developed which can fire on targets automatically, without the need for a command from a human. However these robots are unlikely to see service in the foreseeable future because of the morality issues involved. Other flying robots include cruise missiles, the Entomopter and the Epson micro helicopter robot.

Two robot snakes. Left one has 64 motors (with 2 degrees of freedom per segment), the right one 10.

• Snaking: Several snake robots have been successfully developed. Mimicking the way real snakes move, these robots can navigate very confined spaces, meaning they may one day be used to search for people trapped in collapsed buildings. The Japanese ACM-R5 snake robot can even navigate both on land and in water.
• Skating: A small number of skating robots have been developed, one of which is a multi-mode walking and skating device, Titan VIII. It has four legs, with unpowered wheels, which can either step or roll. Another robot, Plen, can use a miniature skateboard or rollerskates, and skate across a desktop.
• Swimming: It is calculated that when swimming some fish can achieve a propulsive efficiency greater than 90%. Furthermore, they can accelerate and manoeuver far better than any man-made boat or submarine, and produce less noise and water disturbance. Therefore, many researchers studying underwater robots would like to copy this type of locomotion. Notable examples are the Essex University Computer Science Robotic Fish, and the Robot Tuna built by the Institute of Field Robotics, to analyse and mathematically model thunniform motion.