How did Alexander Calder’s earliest motorized mobiles move?

The earliest mobiles created by Alexander Calder were motorized rather than activated by air currents. These initial works featured colored spheres that were driven by motors to move up and down along curving wires at varying speeds.1

While Calder is widely recognized for his later mobile designs—which utilize air currents to rotate suspended metal shapes—these early motorized experiments were instrumental in his development of kinetic sculpture during the 1930s.21