I am doing a Hybird spherical robot which has to walk and roll... For the walking we have chosen a 4 legs so that... the weight falls within our 5 kg limit.... our walking speed should be 0.15m/s..... and I also need help with the material selection... what all factors should I take into consideration to select the appropriate material for the robot...I am looking at HDPE,Aluminium,Steel though mainly plastics.... I will try and upload the picture of our robot.. within a day or two.. please help me..