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Robotic Technology

BigDog robot

By Russ Olexa

November 2009 - With four legs on top of a metal cage stuffed with hydraulic and electronic systems, it looks like a hound from the "Terminator" movies and sounds like a weed whip.

At about the size of a Great Dane, this robot dog offers some unique abilities for the U.S. military.

Funded by a Defense Advanced Research Projects Agency grant, this strange-looking robot is being built by Boston Dynamics, Waltham, Mass., to help transport military gear for soldiers. By acting as a mule of sorts, BigDog allows soldiers to move quickly by shedding their sometimes 80-lb. backpacks that can slow them down in hazardous situations.

Machines that mimic
Founded in 1992, Boston Dynamics is an engineering company that specializes in building dynamic robots and software for human simulation. It began as a spin-off from the Massachusetts Institute of Technology, where Marc Raibert and his colleagues first developed robots that ran and maneuvered like animals.

BigDog is powered by a water-cooled, two-stroke gasoline engine that drives high-pressure hydraulic oil through a system of filters, manifolds, accumulators and other plumbing to the robot's leg actuators, which are low-friction hydraulic cylinders regulated by two-stage servo valves. An integrated radiator system cools the hydraulic fluid.

Each actuator has sensors for joint position and force. Each leg has four hydraulic actuators that power the joints, as well as a fifth passive degree of freedom. BigDog has four legs that are articulated like an animal's with elements to absorb shock and recycle energy between steps.

Its onboard computer controls locomotion; servos used for the leg motion; and a variety of sensors for balance and navigation and to regulate its systems as walking conditions vary. BigDog also handles communications with its human operator.

Sensors for locomotion include joint position, joint force, ground contact, ground load, a gyroscope, light detection and ranging, and a stereo-vision system. Other sensors focus on the internal state of BigDog, monitoring its hydraulic pressure, oil temperature, engine functions and battery charge, among other things.

Work like a dog
Even when BigDog is pushed off balance, climbs over a rocky terrain or loses its footing on a slippery surface, its software counteracts the forces, and it regains its footing without falling. At about 3 ft. long and 2.5 ft. tall, BigDog weighs 240 lbs. and has carried a payload of 340 lbs.

BigDog can run at up to 4 mph and climb 35-degree slopes. It set a world record for legged vehicles by traveling 12.8 miles without stopping or refueling. It can stand up, squat and walk with a crawling gait that lifts just one leg at a time. It can also trot in a way that lifts diagonal legs in pairs, trot with a running gait that includes a flight phase and bound in a special gallop gait.

According to Boston Dynamics literature, BigDog is usually driven by a human operator who uses an operator control unit to communicate with the robot using radios. An operator provides high-level steering and speed input, guiding the robot along its path and controlling its travel speed, as well as telling it to start or stop its engine, stand up, squat, walk, trot or jog. A visual display for the operator provides operational and engineering data. BigDog's onboard control system autonomously operates the legs, provides stability on rough terrain and reflex responses to external disturbances.

With an integrated stereo vision and LIDAR system, BigDog can also follow a human leader without requiring an operator to continuously steer it. BigDog's ultimate goal is to go anywhere people and animals can. FFJ

To see BigDog, click here.

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