Telescopic actuators with articulated rack and pinion gearbox. Linear actuators generally offer low speed and small ratio between the total length when fully extended to the length when compressed. The reason is that in its body rest a rigid piston without the capability to be folded or bended.
The challenge is to fold the rigid element to fit it inside the limited space in between the particle robot's outer and inner shells. So, when the robot compresses all its linear actuators, the robot can move as a spherical mobile robot. While, when extending them, the articulations are converted into rigid links mimicking a rigid piston able to lift the robot.