Zapping liquid metal makes it move in a way that can power wheels

A small metal droplet can propel a wheeled robot forward with a simple electric current. The technique paves the way for larger robots that can trundle like tumbleweeds through unfriendly terrain. Shi-Yang Tang at the University of Wollongong in Australia and his colleagues started with a plastic wheel about five centimetres across with walls along its edges, shaped like a car tyre. Inside the wheel they placed a drop of liquid metal made mostly of gallium.