An arm of a multi-joint robot is nipped with a honeycomb structure material 22 at two side plates 20, 21of the arm to connect the end and the tail of the two side plates 20, 21 of the arm together; meanwhile, the arm is connected with two clapboards 19, 37; the honeycomb structure material 22 is drilled with holes to load in cylinders 17, 18 which contain an engine; two ends of the honeycomb structure material 22 is fixed with the side plates 20, 21 of the arm; by the hole drilled in one of the side plates 20, 21 of the arm, the engine 29, 30 can be arranged in the cylinder which contains the engine, thus achieving the purpose of reducing the arm weight; the invention is suitable for direct transmission, has nice appearance and convenient installation of engine, and is especially suitable for the manufacture of a second arm. |