What were you expecting, pervert!
Shortening the spokes towards the front of the wheel changes its shape, causing the rim's point of contact with the ground to move backwards, behind the centre of gravity. As the wheel then tips forwards, other spokes are heated to deform the rim again and keep the robot rolling along (see diagram).
Shape memory alloys store energy in the form of stresses in their crystalline structure. Passing an electric current through the spokes heats them up, releasing this energy and making them shorter. Allowing them to cool then returns the spokes to their original state. ...
"They would be lightweight and difficult to damage, so I would imagine a good application would be to drop them from a plane into remote areas," he says. The rolling rovers could then perhaps be programmed to roll in a particular direction, bouncing over obstacles, perhaps to deliver cameras to remote locations.
The article mentioned hopes of installing a rechargable battery. But I think some piezoelectrical circuitry would be nifty in these balls, so their motion could generate piezoelectricity for/in them. Couple that with some solar-powered recharging panels and these things could be *virtually* perpetually kinetic. Charge up in the daytime sun; roll around at night on battery and piezo-power. Awesome!