The evolution of Boston Dynamics' quadruped robot: from Big Dog to Spot Mini

Not long ago, a video went viral on WeChat Moments. In the video, a four-legged robot, despite human obstruction, struggled to open a door and finally passed through smoothly. Everyone who watched the video was shocked by the robot's "perseverance". Overnight, the robot became a well-deserved "Internet celebrity". In fact, this "Internet celebrity" is a four-legged robot named "Spot Mini" developed by Boston Dynamics in the United States. This is not the first four-legged robot launched by Boston Dynamics.

As early as 2005, the release of Big Dog made Boston Dynamics famous. In the following decade, Boston Dynamics launched a series of quadruped robots, which received strong responses from the outside world. Therefore, this article will take a chronological view of the development process of Boston Dynamics' quadruped robots and take you to appreciate the charm of the "Big Dogs".

The original intention of the birth of robots is to serve humans, liberate humans from repetitive, tedious and even dangerous work, and then invest limited human resources into more valuable production labor processes.

In 1920, the word "robot" was first proposed by Czechoslovak writer Karel Capek, and since then, robots have begun their long development process.

Nowadays, robots can be seen everywhere in our lives, but most of them are just "mobile computers" that can only perform simple and repetitive operations according to pre-set program instructions. This also limits our understanding of robots to a certain extent.

Once traditional cognition is formed, the emergence of new things will be extremely subversive. In 2005, a video of about 3 and a half minutes shot by Boston Dynamics in the United States attracted widespread attention from all walks of life on the Internet. The video content shows that a four-legged robot can still walk flexibly while carrying heavy objects, and can respond quickly to external interference and always maintain the balance and stability of the body.

For a time, the discussion on the development prospects of robots once again became a hot topic, and Boston Dynamics naturally became the focus of everyone's attention.

Boston Dynamics was founded in 1992 and mainly conducts research related to robots. Its goal is to create intelligent robots that can work flexibly in the real world like humans or animals. Since its establishment, it has attracted many top scientific research talents from major universities around the world. The reason why Boston Dynamics has such a strong appeal is closely related to its founder Marc Raibert.

Mark Reibert is a typical academic entrepreneur. After obtaining his doctorate from MIT, he founded the CMU Leg Lab at Carnegie Mellon University and served as an associate professor. In 1986, Mark Reibert returned to MIT to continue his work on robot development and research, and eventually left MIT in 1992 to found today's Boston Dynamics.

In 1950, American science fiction writer Isaac Asimov proposed three laws that robots must follow in his masterpiece "I, Robot", which were later called the "Three Laws of Robotics", namely:

A robot may not injure a human being or, through inaction, allow a human being to come to harm.

A robot must obey the orders given to it by human beings, except where such orders would conflict with the First Law.

A robot must protect its own survival as long as this does not conflict with the First or Second Laws.

These three laws provide a reference for the research and development of robots to a certain extent, and emphasize the safety standards that need to be followed in the process of robot research and development. However, the premise for the application of these three laws is that the robots are intelligent enough. At present, the intelligence level of robots is still relatively low. Therefore, these three laws do not yet have sufficient scope for use.

To make robots more intelligent, the first thing to do is to enable them to move freely like humans or animals. In Mark Repot's opinion, to achieve this goal, robots must have the following three capabilities:

Balance and dynamic movement capabilities: The robot can maintain balance and move freely anywhere and on any terrain, which means that the robot's working range is effectively expanded.

Movement control capability: This means that the robot can flexibly manipulate objects (such as using a keyboard and remote control) while moving freely, which means that the robot can easily complete various operational tasks while moving.

Mobile perception capability: refers to the robot's ability to sense the stable existence of objects in space and avoid obstacles even if its line of sight moves elsewhere. This means that the robot can draw a map of the location of obstacles in the surrounding environment, so that it can effectively avoid obstacles while moving forward or backward.

Boston Dynamics is carrying out various research and development work on robots based on the above three points.

Big Dog, affectionately called "Big Dog", is a quadruped robot launched by Boston Dynamics in 2005. It is this quadruped robot that made Boston Dynamics famous. Big Dog abandoned traditional wheeled or tracked robots and turned to quadruped robots because quadruped robots can adapt to more terrains and have stronger passing performance.

In the promotional video released by Boston Dynamics, Big Dog can react sensitively to human kicks from the side and always remain standing even when carrying heavy objects.

Big Dog is about 1 meter tall and weighs about 109 kg. It can carry a 45 kg payload and walk or run freely. Its maximum speed can reach 6.4 km/h and its maximum climbing angle can reach 35 degrees. At the same time, Big Dog can adapt to a variety of complex road conditions and can walk freely even in snow or mud. Even if someone applies external force to its side, Big Dog can quickly adjust the movements of its four legs to keep its body stable and avoid falling. The reason why it has such powerful capabilities is inseparable from its sophisticated design structure and meticulous computing system:

Big Dog is based on the body structure of quadrupedal mammals and is assembled mechanically. The articulated structure of its limbs can effectively absorb impact and play a shock-absorbing role. It has 16 degrees of freedom as a whole and can move freely in both horizontal and vertical directions. In addition, Big Dog is powered by a gasoline engine, which drives the hydraulic system, using the hydraulic system as the driving output power to control the movement of each limb and achieve flexible movement of the body.

The motion control system installed in Big Dog effectively ensures the independence of the robot's movement, and only requires a small amount of human intervention for the robot to complete the given task. The motion control system detects limb status information through sensors installed in areas such as joints and soles, and uses gyroscopes and inertial sensors to monitor the balance and stability of the body, so that it can respond quickly to balance interference factors in a timely manner, effectively ensuring the stability of the center of gravity, allowing the robot to maintain a stable posture and move forward.

At the same time, it also has high navigation intelligence. It can autonomously perceive the surrounding environmental information through lidar sensors and stereo vision sensors, and then build a terrain model in a virtual environment. At the same time, it uses its own computing computer to plan the path and relies on the motion control system to reach the target point along the planned path.

Although Big Dog has powerful functions, it was ultimately not adopted by the US military due to its high noise during operation.

LS3 is also known as "Alpha Dog", where "LS" is the abbreviation of "Legged Squad". LS3 robot is a new quadruped robot launched by Boston Dynamics after Big Dog, and was first publicly unveiled in 2012. Compared with Big Dog, LS3 is larger in size, has a stronger load capacity, moves faster, and has greatly improved practical performance.

In the promotional video released by Boston Dynamics, the LS3 can nimbly climb hills or pass through rugged roads even when loaded with heavy objects.

The LS3 is about 1.7 meters tall and weighs about 509 kilograms. It can carry a 181-kilogram payload and walk and run freely (in a flat ground test, the LS3 set a record of walking freely while carrying a 500-kilogram load). The fastest moving speed can reach 45 kilometers per hour. In actual tests, the LS3 can still maintain a relatively fast forward speed on rugged mountain roads.

It has 12 degrees of freedom and is powered by a gas or diesel engine. The engine drives the hydraulic system, which is used as the driving output power to control the movement of each limb and achieve flexible movement of the body. With sufficient fuel, the LS3 can run for 24 hours and has a maximum mileage of 32 kilometers.

LS3 inherits the mobility characteristics of Big Dog and uses terrain sensing, obstacle avoidance and GPS to ensure safety during the process, so that it can reach the target location smoothly. In addition, LS3 uses computer vision technology to achieve automatic tracking, so it can follow the target person without a dedicated driver.

LS3 participated in the US military's combat training missions, but because its own operating noise problem was not effectively solved and its faults were difficult to repair, it was eventually abandoned by the US military.

Wild Cat, also known as the "Wild Cat Robot", is a four-legged robot launched by Boston Dynamics in 2013. Its predecessor is Cheetah, or the "Cheetah Robot". Cheetah has multiple cables connected to its body, which means it can only be a robot that runs in a laboratory.

In a promotional video released by Boston Dynamics, Cheetah set a robot running speed record of 48 km/h on a treadmill.

Although Cheetah can only run in the laboratory, it has set a running speed record of 48 km/h. Cheetah uses an articulated back structure, which allows Cheetah's back structure to move flexibly during its running process to better coordinate the overall posture, improve stride length and running speed.

In the promotional video released by Boston Dynamics, Wild Cat can run agilely outdoors, easily jump over obstacles, and even perform emergency stops and U-turns while running.

We can think of Wild Cat as the "wireless version" of Cheerah. It is about 1.17 meters tall, weighs about 154 kilograms, and can move at a maximum speed of 32 kilometers per hour. Wild Cat can adapt to a variety of terrains and can keep moving at a speed of about 16 kilometers per hour under complex road conditions. In addition, Wild Cat can also achieve quick jumps and quick turns, which greatly improves its flexibility compared to Big Dog and LS3.

Wild Cat has 14 degrees of freedom and is powered by a methanol engine. The engine drives the hydraulic system, which uses the hydraulic system as the driving output power to control the movement of each limb and achieve flexible movement of the body. In addition, Wild Cat uses a laser rangefinder to accurately measure the robot's height from the ground and its own posture, and calculates the movements required by the limbs through a dynamic control algorithm to achieve stable operation.

Although the Wild Cat uses a methanol engine, the running noise is still relatively high. If it is powered by battery energy in the future, the Wild Cat will be able to run with low noise, improve its own concealment, and thus play an excellent role on the battlefield.

Boston Dynamics has developed three quadruped robots, Big Dog, Cheetah and LS3. Although these robots have excellent performance, they have not been widely used due to the prominent noise problem. Therefore, Boston Dynamics has fully summarized past experiences and lessons and created a new quadruped robot called "Spot".

In the promotional video released by Boston Dynamics, the Spot robot achieves low-noise operation, can use its two limbs to jump on the spot without falling, and can go up and down stairs flexibly.

Spot is a quadruped robot launched by Boston Dynamics in 2015. It is about 0.94 meters tall and weighs about 75 kilograms. It can carry a 45-kilogram payload and move freely or run. From the official video released by Boston Dynamics, Spot's climbing speed is faster than Big Dog and its steps are more sensitive.

Spot has 12 degrees of freedom and is powered by batteries, which drive the hydraulic system, which is used as the driving output power to control the movement of each limb and achieve flexible movement of the body. The use of battery energy effectively controls the robot's operating noise, but at the same time, the robot's operating time is also affected. When fully charged, Spot can run continuously for about 45 minutes, which is in stark contrast to the LS3's maximum continuous operation time of 24 hours.

Spot uses lidar sensors and stereo vision sensors to perceive surrounding road information, so as to effectively avoid road obstacles and coordinate the movements of its limbs. However, Spot's movement does not entirely rely on this sensor system, sometimes it also relies on "feeling".

In the video officially released by Boston Dynamics, there is a scene where Spot is climbing a set of stairs alone, but it cannot adjust the step height and stride according to the height and width of the stairs. Although each step is shorter and wider, Spot still maintains a higher step height and a shorter set stride, which leads to a mistake during the climbing process. Therefore, we can imagine that if the height and width of each section of this set of stairs are different, then Spot may make more mistakes.

The reason for this mistake is that when Spot is climbing the stairs, the lidar sensor and stereo vision sensor cannot capture complete road information. Therefore, Spot needs to estimate the movements of its limbs based on the only small amount of road information. Although this has an almost negligible impact on Spot's ability to pass, it provides typical material for Boston Dynamics to further improve its robot's behavioral capabilities.

In November 2017, Boston Dynamics unveiled its latest quadruped robot, Spot Mini. Compared with Spot, Spot Mini is smaller in size and has a pair of robotic arms on its head, with a gripper on top that can flexibly manipulate objects.

In the promotional video released by Boston Dynamics, Spot Mini used its own robotic arm to struggle to open the closed iron door despite human obstruction.