A transmission is presented, including a spool having a bore. An outer member disposed on the spool, and a cord is configured to at least partially wrap around the outer member. The outer member is configured to constrict and unconstrict to a force applied to the outer member. In this way, rotation of the spool causes a tension force to be applied to the cord, and a greater tension force in the cord will cause the outer member to constrict more than a lower tension force in the cord.