Passive transmissions, and methods of making and using same

A variable transmission, comprising:

• a spool comprising a rigid core defining a bore to receive a shaft;
• and
• a constrictable outer member disposed about a circumference of the spool, the constrictable outer member comprising at least one elastically deformable element aligned with the rigid core and being configured to elastically deform between a first radius, corresponding to an unloaded state, and a second radius, corresponding to a fully loaded state, responsive to an applied force directed toward the rigid core and
• a cord configured to at least partially wrap around the constrictable outer member and to apply thereto, when tensioned, a force directed to the rigid core,
• wherein a magnitude of elastic deformation of the at least one elastically deformable element toward the rigid core is related to a magnitude of an applied force, with a greater applied force causing a greater elastic deformation of the at least one elastically deformable element toward the rigid core.