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Quadruped Robots > The EPFL Cheetah-Cub

Cheetah-Cub. The first robotic cat

Most of us are familiar with Boston Dynamic's long-running BigDog robot project, which has created and continues to improve robots based on the canine model, able to traverse any terrain a human can, whilst carrying far heavier loads than any dog could, into a combat zone.

However, the canine model isn't the only viable quadruped model that exists in nature, and each model has advantages and disadvantages of its own.

The Switzerland-based university Ecole Polytechnique Fédérale de Lausanne, or EPFL for short, has developed in its biorobotics laboratory, a tiny prototype robot about the size of a house cat, which uses the cheetah's joint and locomotion model instead of the canine's. It is basically, the first robot to use a feline walking and running model for navigating terrain.

The feline model does have certain advantages. The cheetah in particular is built for swift acceleration, and extreme agility. A robot based on the same locomotive model would not have the exhaustion problems a biological organism has, and could accelerate quickly and smoothly, whilst keeping that pace up as it darts around the landscape.

The researchers have search and rescue applications in mind for their robot, but it would also work well as a military robot. Not a pack-bot as BigDog is built for; not a steady-paced bulk equipment carrier intended to work as part of a pack, but instead, a fast paced, highly agile unit able to operate solo, and react lightning-fast to real-time changes in its environment, like a real feline does.

The prototype is needless to say, nowhere near as agile as an actual cat, at this point in time. However, it is the fastest quadruped robot ever created, relative to its size and weight. During tests, it demonstrated its ability to run nearly seven times its body length in one second.

Because its legs are modelled on that of the Cheetah, bending and flexing the same way, pivoting in the same places and with the same freedom of movement an adult cheetah's limbs have. Each leg is divided into three segments, proportioned identically to a feline. Springs are used to reproduce tendons, and actuators small motors that convert energy into movement are used to replace the muscles.

One of the key features of the robot is how remarkably stable it is. Even when running at full speed, this stability remains present. Tested on a simple assault course involving flat platforms of varying heights, the stability was unaffected. The only reason a more complex assault course was not considered, is simply that the bot's AI is not yet capable of working out complex terrain in real-time. In theory, the robot's stability should not change, even on rough, broken terrain. This means it could change direction at any time, in any direction with equal efficiency.

Cheetah-Cub navigating the halls on a leash.

“This morphology gives the robot the mechanical properties from which cats benefit, that’s to say a marked running ability and elasticity in the right spots, to ensure stability,” explained Alexander Sprowitz, one of the biorobotics laboratory researchers. “The robot is thus naturally more autonomous.”

Future research directions include developing the controlling AI so the robot can handle a wider variety of terrain, and of course creating larger versions with increasing agility capability. By replicating the designs found in nature, the whole point of biorobotics is to take the advantages of those designs, and improve on them with the unflagging nature of robotics.

Once they have a model that is just as agile as a fit house cat, then the cheetah-cub robot will be a serious contender for search and rescue operations, a trained, loyal, obedient cat being rather hard to find. A robot with the loyalty of a dog and the reflexes of a cat would be an invaluable asset for pinpointing survivors or navigating narrow, rickety structures to bring supplies, or even ropes for other rescuers to follow behind the bot.





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Cheetah-Cub - a compliant quadruped robot

Towards Dynamic Trot Gait Locomotion: Design, Control, and Experiments with Cheetah-cub, a Compliant Quadruped Robot (Paper)

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