ETH robot dog solves Rubik's Cube with its paws
It takes 'ANYmal' eight to nine minutes to complete a full run. During this process, the four-legged robot must tilt, rotate, and stabilize a 4.6-kilogram cube in a controlled manner.
ANYmal holds the cube steady with one front paw. It uses the others to rotate two layers by 90 degrees. Afterward, it changes its position and begins the next step. This sounds simple, but it requires a great deal of dexterity from the four-legged robot.
The Rubik's Cube measures 40 centimeters per edge. In the trials, ANYmal succeeded three times in solving it completely without human assistance. It took about 30 movement steps each time, including cube rotations and position changes. The research team at ETH Zurich has published its results in a scientific paper.
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Scan first, then rotate
Before ANYmal can get started, it must recognize the colors of the cube. To do this, it walks around it and captures the visible sides with its cameras. To see the underside as well, it tips the cube over once.
The software reconstructs the position of all colored squares from the recordings. Based on this, the so-called Kociemba algorithm calculates a solution with as few cube rotations as possible. The method was developed by Herbert Kociemba. The motion planning translates the calculated rotations into actions that ANYmal can perform with its legs.
The paws learn new tasks
The movements require precise control of the legs. ANYmal must exert enough force to rotate the cube layers. At the same time, the robot must not lose its balance or accidentally shift other layers.
To learn these movements, the researchers rely on so-called Reinforcement Learning. In this process, an AI first trains the movement sequences in a virtual environment. Through repeated attempts and rewards for successful actions, it learns to control its movements in a targeted manner. From the results, the researchers develop a controller that works with camera images and sensor data from ANYmal.
The individual tests show how demanding the task remains. Both tipping movements succeeded 15 times out of 15 attempts. For counter-clockwise rotations, 13 out of 15 attempts were successful, and ten for clockwise rotations.
More than a Rubik's Cube trick
In previous experiments, four-legged robots have already pressed buttons or opened doors with their paws. However, solving a Rubik's Cube requires several precise, coordinated movements.
The researchers want to demonstrate how legged robots could use their legs as tools in the future. Tasks where a robot needs to hold, move, or operate objects are conceivable.
The three complete solutions were achieved under controlled conditions on a flat surface. The researchers also tested individual movements on cobblestones and slippery surfaces. In these cases, the robot sometimes reached its limits. Whether ANYmal can reliably handle comparable tasks in everyday life remains to be seen.
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