Spherical robot

The operating principle relies on unbalancing the interior of the sphere. In the most common variant — the pendulum drive — a weight (pendulum) is suspended inside the shell on a motorized axle. Shifting the weight forward moves the center of mass past the sphere contact point, creating a torque so the ball starts rolling in that direction. Tilting the weight sideways produces a turn. In the flywheel (momentum) variant the robot uses conservation of angular momentum: spinning up or braking an internal flywheel produces a reaction that rotates the shell. There are also hamster-ball variants (an internal vehicle driving along the inner wall), shell-deformation and gyroscopic drives. Inertial sensors (IMU) and encoders continuously measure the sphere orientation, and the control loop corrects the mass position, because — unlike a wheeled robot — the entire electronics rotate together with the shell.