A mechanism for transmitting rotational power comprising: a link extending along a closed loop and continued by a succession of portions each having a longitudinal direction tangent to the closed loop; and temporary unification means comprising a plurality of self-locking means distributed at least along an active portion of a first drive circle, and comprising at least one rigid locking element simultaneously pressing against a first support surface of the first rotating element and a second support surface of a link portion facing the locking element. The first and second support surfaces are arranged so that one locking element of the first drive circle active portion is jammed between the support surfaces and is capable of self-unlocking when the corresponding self-locking means leaves the active portion. One of the support surfaces is a tangential gripping surface that is parallel to the longitudinal direction of the link portion against which the locking element presses.