An apparatus includes a flywheel, a first pivotable caliper, a first magnet supported by the first caliper opposite the flywheel, a second pivotable caliper and a second magnet supported by the second caliper opposite the flywheel. In one implementation, the apparatus further includes a first cam follower coupled to the first caliper, a second cam follower coupled to the second caliper and at least one cam member including a first cam surface against which the first cam follower moves and a second cam surface against which the second cam follower moves, wherein movement of the at least one cam member pivots the first caliper and the second caliper to move the first magnet and the second magnet relative to the flywheel. In another implementation, the apparatus further includes a strain gauge carried by the first caliper to output signals indicating braking torque.

Described herein is a system, method of use and Self Retracting Lifeline (SRL) apparatus using a system that governs a dynamic response between members causing a halt in relative motion between the members. Magnetic interactions, eddy current drag forces and centrifugal and/or inertial forces may provide various mechanisms of governing movement.

An electromagnetic braking device includes a brake disk, a fixed disk, an armature, a biasing member for biasing the armature, and a stator for attracting the armature. In a stator magnetic circuit member, a first yoke, a permanent magnet, and a second yoke are arranged in this order from one end to the other end of a U shape. In a rotatable state or a rotation braking state, even when the coil energization is OFF, the rotatable state or the rotation braking state is maintained. When a current of a predetermined magnitude flows through the coil in a first direction in the rotatable state, the state shifts to the rotation braking state, and when a current of a predetermined magnitude flows through the coil in a second direction in the rotation braking state, the state shifts to the rotatable state.