An arm assembly for a cover system includes a force mechanism contained within a hollow arm of the assembly that includes a resiliently compressible element, such as a compression spring, with a cable or wire extending through the element. The cable is fastened at one end to an end cap that bears against one end of the compression spring. The opposite end of the cable is fastened to a base mounted to the container body. The base includes a pulley about which the cable is wound as the arm pivots relative to the base. As the arm pivots and the cable winds about the pulley, the end cap bears against the spring to compress the spring.