An apparatus for converting rotational motion into radial motion may include a motor, and arm assembly, and, optionally, a panel. The motor may include two coaxial rotors and a motion generator coupled to the rotors. The arm assembly may include first and second arm attached at their proximal ends to the first and second rotors, respectively. The optional panel may be attached to the distal ends of the arms. The distal ends of the arms may be spatially fixed with respect to one another but rotatable with respect to one another, so that counter-rotation of the rotors can cause both distal ends and the panel, if present, to move radially away from the rotors' axis.