A robotic arm utilizing two pulleys connected by two metallic drive bands wound in opposite directions and rotatably attached to the pulleys. The metallic drive bands may include multiple metal strips separated by a visco-elastic material. One end of one drive band is attached to the pulley by a pin. A positioning mechanism is provided to adjust the tension of the band. The positioning mechanism includes a retaining piece, a wedge piece and an adjustment piece. The retaining piece is laterally movable and has an attachment point to the metal band and a slanted face. The wedge piece is vertically-movable and has a face abutting the slanted face of the retaining piece. The adjustment piece attaches the wedge piece to the pulley and moves the wedge piece vertically.