I really wanted to make it metal or aluminum but needed to make this as easy and cheap as possible... the arms I made was just rubber-sheet (foamies is that called?) reinforced with plastic card (sintra) and the hinges were all plastic tubes, uses just 3 servos; a 9g servo, a 19g servo and a 37.2g standard servo (salvaged from an old tamiya car) then powered by my old electric RC helicopter's 11.1v battery (had to make the voltage regulator circuit so that it would output only 5v)