BigDog — an infantryman’s best friend

Whether it’s loping through the undergrowth, scrambling up snowy banks or skittering across the ice, BigDog is an astonishing and somewhat unsettling sight.

Developed for the US defence research agency DARPA by MIT spin-out Boston Dynamics, the four-legged robot has been designed to carry soldiers’ equipment across terrain too rugged and difficult for existing tracked and wheeled vehicles.

Around 1m tall and 1.1m long, the 109kg quadruped is able to stand, squat, crawl, trot, run (its current top speed is 7mph) and even bound. It has been tested in mud, snow and water, has carried a 154kg load and last summer it set a world record for legged vehicles when it completed a 12.8-mile, eight-hour hike without stopping or refueling.

The power supply is a two-stroke internal combustion engine, the eerie whirring noise of which adds to the robot’s air of menace. The engine drives a hydraulic pump that delivers oil through accumulators and other devices to the hydraulic leg actuators.

Sensors on these actuators measure joint position and force, while around 50 sensors elsewhere in the robot measure the acceleration and attitude of the body.

Along with visual data gathered by stereo cameras and a LIDAR system, this information is processed by an onboard computer that carefully coordinates the behaviour of the legs, giving the system stability on rough terrain and enabling reflex responses to external disturbances, that would otherwise tip the machine over.

Boston Dynamics’ Marc Raibert, who heads up the BigDog team, explained that there are three ways to control the robot: ‘An operator can drive it from a portable joystick. It can navigate using GPS waypoints, with a computer visual system used to avoid trees. Or, it can follow a human leader using a specialised visual tracking system. In all cases, the onboard computer and control system automatically do the walking and balancing, including dealing with local roughness of the terrain.’

Although the company is now nearing the end of the funding for BigDog, Raibert is hopeful over its chances to take the technology to the next level through DARPA’s Legged Support System (LS3) project.

The goal of this follow-up programme is to develop a legged system that can travel 20 miles and carry 180kg of payload in addition to its fuel payload. Planned improvements to BigDog that could see it meet these requirements include a stronger mechanical design, the ability to right itself should it fall over, plus alternative power sources that would enable it to travel further and switch to a quieter operating mode if necessary. According to the company, this could make use of either a quieter four-stroke engine or a form of hybrid power system.

Perhaps the team could draw on other DARPA-funded research into robot power systems. Robotics Technology is working on the EATR robot, a system that munches through biomass to make its own fuel. In response to tabloid stories about ‘corpse-eating robots’ the company stated that the robot is ‘strictly vegetarian’ — a relief to readers terrified by the thought of ravenous robo-dogs turning on humans.