If you're really interested in robots—or rather, who isn't… you've probably heard the term "robot dog" a lot. They seem to be everywhere, which raises the question: why are so many quadruped robots designed to look like dogs?
To answer this question, we interviewed two experts in the field of robotics, IEEE Senior Member Ming Liu and IEEE Member Jayakrishnan Thrivikraman Nair.
Liu explained that the robot dog is part of the robot family and is referred to as a "quadruped," which clearly means "four-legged." The reason why most quadruped robots are designed as dogs, rather than horses or rabbits, is because of their unique knee structure.
“Unlike horses, whose forelegs point forward and hind legs point backward, dogs have all four knees pointing backward. This design helps ‘dog-shaped’ robots complete tasks such as climbing stairs, providing more leg movement space and better protection against impacts,” Liu said. “Companies such as Boston Dynamics’ Spot, MIT’s Cheetah3, and Unitree’s Go1 all use a backward knee design, which is consistent with the shape and appearance of dogs.”
“When a quadruped robot is performing a task of going upstairs, the backward elbow design provides a larger, collision-free workspace for the legs,” Liu said. “When going downstairs, the situation is reversed. The forward knee design becomes more advantageous, so the robot mentioned above tends to go downstairs backwards. In addition, there are quadruped robots that can switch the direction of their elbows.”
Dogs' legs are simpler
Nair explains that dogs tend to have a low center of gravity, which makes them more stable.
He said, "A dog's forelegs are significantly different from those of larger animals, with the last segment being considerably shorter in length. This also ensures that the shape and proportions of the forelegs and hind legs are identical, thus simplifying hardware replication and gait control."
Advantages of quadruped robots
One of the most prominent uses of robot dogs is for monitoring and inspection.
They can be used in search and rescue operations, or in places that are too small or too dangerous for humans.
Nair said, “This is the simplest form of statically stable movement that can traverse challenging terrain. It offers the best balance of cost, controllability, and the ability to walk on rough terrain. The design has four legs and can move in three different gaits: walking, trotting, and galloping.”
A comparison of two-legged and four-legged robots
“Although bipedal robots can perform similar tasks, the mobility of bipedal animals is far inferior to that of quadrupedal animals,” Liu said. “In addition, the cost of building and maintaining bipedal robots is several times that of quadrupedal robots.”
Disadvantages of quadruped robots
However, quadrupeds also have some drawbacks,” Liu said. “Their energy efficiency is often very low; most quadruped robots can only work continuously for about an hour. In addition, the gait noise of these robots is loud, which some people may find unbearable. These shortcomings will hinder the wider application of quadruped robots in daily life.”
