A self-braking pulley for controlling a rate of extraction of a tether coupled with the pulley, the pulley comprising: a spool for receiving a tether, the spool being arranged to rotate about an axle of the pulley as the tether is removed therefrom; a braking assembly for applying a braking force to the spool, the braking assembly comprising a shoe plate, a follower gear and an axle, the shoe plate and the follower gear being rotationally coupled with the braking assembly axle such that rotation of the follower gear causes rotation of the shoe plate, the braking assembly further comprising a plurality of brake pads arranged to contact a brake drum in dependence of a rate of rotation of the spool about the pulley axle, each brake pad being separately disposed upon a respective brake shoe, each shoe being hingedly coupled at a leading end thereof during a rotation of the plate within the drum as the tether is unwound from the spool, to the shoe plate at angularly separate positions around the periphery thereof such that the contact area of the brake pads with the drum varies in dependence of a rate of rotation of the plate, a trailing end of each shoe being coupled via an elastic member to the trailing end of the rotationally adjacent shoe; and a drive assembly, the drive assembly comprising a wheel having a plurality of serrations disposed along an outer perimeter thereof and a drive gear rotationally coupled with the wheel, the wheel and the drive gear being arranged to rotate about the pulley axle such that rotation of the wheel causes rotation of the drive gear, the drive gear further being rotationally coupled with the follower gear such that rotation of the drive gear causes rotation of the follower gear, the drive assembly being engagable with the spool via an engagement member comprising a pawl which is pivotally coupled to the spool about a pivot, the pawl having a centre of mass which is disposed to one side of the pivot, such that a proximate end of the pawl extends closer to the pivot than a distal end of the pawl, the pawl being reconfigurable from a neutral configuration in which the proximate end of the pawl extends away from the wheel to a drive configuration in which the proximate end of the pawl abuts the serrations on the wheel to rotationally couple the spool with the drive assembly for driving the braking assembly in dependence of a rate of rotation of the spool about the pulley axle. a spool for receiving a tether, the spool being arranged to rotate about an axle of the pulley as the tether is removed therefrom; a braking assembly for applying a braking force to the spool, the braking assembly comprising a shoe plate, a follower gear and an axle, the shoe plate and the follower gear being rotationally coupled with the braking assembly axle such that rotation of the follower gear causes rotation of the shoe plate, the braking assembly further comprising a plurality of brake pads arranged to contact a brake drum in dependence of a rate of rotation of the spool about the pulley axle, each brake pad being separately disposed upon a respective brake shoe, each shoe being hingedly coupled at a leading end thereof during a rotation of the plate within the drum as the tether is unwound from the spool, to the shoe plate at angularly separate positions around the periphery thereof such that the contact area of the brake pads with the drum varies in dependence of a rate of rotation of the plate, a trailing end of each shoe being coupled via an elastic member to the trailing end of the rotationally adjacent shoe; and a drive assembly, the drive assembly comprising a wheel having a plurality of serrations disposed along an outer perimeter thereof and a drive gear rotationally coupled with the wheel, the wheel and the drive gear being arranged to rotate about the pulley axle such that rotation of the wheel causes rotation of the drive gear, the drive gear further being rotationally coupled with the follower gear such that rotation of the drive gear causes rotation of the follower gear, the drive assembly being engagable with the spool via an engagement member comprising a pawl which is pivotally coupled to the spool about a pivot, the pawl having a centre of mass which is disposed to one side of the pivot, such that a proximate end of the pawl extends closer to the pivot than a distal end of the pawl, the pawl being reconfigurable from a neutral configuration in which the proximate end of the pawl extends away from the wheel to a drive configuration in which the proximate end of the pawl abuts the serrations on the wheel to rotationally couple the spool with the drive assembly for driving the braking assembly in dependence of a rate of rotation of the spool about the pulley axle.