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Building a Working Robot Step-by-Step

Engineering And Mechanics: Teaching A Robot To Walk

Asimo began in 1986 as a technological and design challenge put to the engineers of the Honda Motor Company. Seeking to develop revolutionary new technology, the engineers first had to decide on the ideal tasks for a walking robot to perform in human society. Their goal was to create a robot helper for hazardous or menial jobs, for housekeeping chores, or to assist in the care of the elderly and handicapped. The robot would have to be able to walk up and down stairs, maneuver on uneven terrain and around objects in a crowded room, and access the same places that humans do. Ultimately, it was determined that the best model for the robot's design would be the human body itself.

One of the engineers' greatest challenges was duplicating the walking motions of humans. We don't have to think consciously about the endless series of movements that allow us to walk upright – maintaining our balance, shifting our weight just so to compensate for each step or turn, recovering our balance after a misstep. The process has become reflexive, but watch a baby just learning to walk and you will quickly see how complicated and difficult a process it can be.

Before they could build their robot, Honda's engineers first had to see if they could make it walk. They studied a whole range of motion, from the legs of insects to the motion of a mountain climber with prosthetic legs (which more closely resemble robotic legs). From these, they learned all of the many, often almost imperceptible movements that are made – from our heads down to our toes – when we walk. One of the things they learned during this study was that we shift our weight with our entire bodies to maintain balance, and that the toes of the human foot are helpful in this process. They then designed a set of robotic legs to put what they had learned into practice, trying to duplicate human motions through mechanical means. They even gave Asimo soft projections on its feet that act as its toes.

The Honda engineers studied the way joints function in the human body and incorporated them into Asimo in the form of servo-motors – small but powerful motors with a rotating shaft that moves limbs or surfaces to a specific angle as directed by a controller. Once the motor has turned to the appropriate angle, it shuts off until it is instructed to turn on again. Asimo includes twenty-six joints, or “degrees of freedom,” as engineers call them. A single degree of freedom allows for movement either right and left or up and down. Asimo has two degrees of freedom in its neck and six in each arm and leg.

Asimo went through several early incarnations, developing from a pair of legs that would take as much as twenty seconds to take a single shuffling, or “static,” step to the much more humanlike “dynamic” walking. Dynamic walking meant that Asimo leaned into the next step, shifting its weight and moving the other foot forward to catch itself, so that rather than falling forward, it walked forward. By the sixth prototype, the engineers had solved the problem of walking and had a robot that could walk up an incline, up stairs, and on uneven terrain. With the most recent Asimo Walking Technology, the robot can even predict its next movement in real time and shift its center of gravity in anticipation of it.

Once they had a machine that could walk, the engineers needed an upper body and head for their creation. Once again, they chose the human body as the basic model for Asimo, initially making him six feet, two inches (188 centimeters) tall and 386 pounds (175 kilograms). Successive models were scaled down to four feet (122 cm) and 115 pounds (52 kg). At that size, the engineers reasoned that Asimo would be less intimidating to people, even those who are seated, but still tall enough to work at a standard table or counter and reach doorknobs and light switches.

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