A robot that hitch-hiked around Europe and Canada has been smashed to pieces in the United States.

HitchBOT, who was created as part of a social experiment to see whether robots can trust humans, had spent weeks successfully hitchhiking his way from town to town.

The robot was trying to cross the United States and had got as far as Philadelphia.

One of HitchBOT's creators Dr Frauke Zeller, Assistant Professor at Ryerson University in Toronto, explains what happened.