The US Defense Advanced Research Projects Agency has renewed a $1.5m contract with the University of Southern California to develop smart robo-dogs.

The robots were developed by Stefan Schaal, an associate professor in the USC Viterbi School of Engineering's Department of Computer Science.

The robo-mutts have four pointy feet ending in small balls, and are being engineered to make their way across a treacherous terrain of broken rocks.

Schaal, who began working on the problem more than a year ago, said that four-legged and six-legged robots have been walking around for years, but mostly on smooth surfaces where wheels are a more efficient way of getting around.

"What you really want legged robots for is to negotiate difficult terrain," he explained.

The robots are built by Boston Dynamics and come with an onboard computer chip connected to sensors.

The device is continually aware of the location of its centre of gravity, and adjusts a "smooth walking pattern generator with the selection of every foot placement to follow a stable trajectory".

The robot calculates where and how it should proceed "based on the current position, velocity and acceleration" of its legs. If one effort fails, the dog learns from its mistake and tries another route.

After 15 months of experimentation, which involved sending back mechanical dog "bodies" at a rate of one a month, but saving each one's digital electronic experience, the dogs can now move, but not very quickly.

Maximum speed at this stage of development is 1.6cm a second, a little faster than the 1.2cm/sec of the Mars Sojourner robot.

The goal in the next phase of the study is to triple the speed and double the difficulty of the terrain so that the dogs also have to climb rocky ground with a sharp slope.