Teaching robots to walk on two legs turned out harder than making them fly
An airliner is practically a flying robot: its autopilot can handle takeoff, cruise and landing while two humans supervise. Yet engineers still struggle to build a two-legged machine that walks as reliably as a toddler. Honda's famous ASIMO needed flat floors, and onlookers joked it looked desperate for a bathroom.
Every robot combines four ingredients: a power source, a mechanical body, electrical circuits for control, and software that decides what to do, whether by remote control, artificial intelligence or a mix. Batteries are the usual power, most often heavy but dependable lead-acid types. Motors do most of the moving, while linear actuators driven by oil or compressed air push factory arms in and out.
Walking exposes the difficulty. ASIMO relied on the zero moment point method, constantly adjusting so that gravity and the jolts of each step were cancelled by the floor pushing back, leaving nothing to tip it over. It worked, but only on level ground. In the 1980s Marc Raibert's MIT Leg Laboratory took another route: a one-legged robot that stayed upright by hopping, like a person on a pogo stick, leaping toward whichever side it began to fall. The trick scaled up to a biped that could run and somersault and a four-legged machine that trotted and bounded. A third idea, passive dynamics, lets swinging limbs carry their own momentum and might be ten times more efficient.
Wheels have surprises too. Carnegie Mellon's Ballbot, roughly person-sized, balances on a single sphere, and two-wheeled robots use a gyroscope to sense a fall and correct the wheels hundreds of times each second. Climbing robots borrow from gecko toe pads to scale vertical glass, while snake robots squeeze through tight spaces.
Muscles are another frontier. Air muscles swell by up to 42 percent when inflated, and electroactive polymers can stretch as much as 380 percent under electric current. Experimental carbon nanotube fibres might one day stand in for a human biceps with a strand around 8 millimetres thick.
Source: Robotics
