will be described later in this specification drum 10 will be referred to herein as a storage drum i e the drum on which the spring is initially coiled proceeding next to fig1 b an output drum is shown generally at 20 to include an axial hole 22 a cylindrical body 24 and a pair of walls 26 and 28 a hole 29 is provided on body portion 24 the purpose of which will become apparent shortly output drum 20 also includes a cord spool 30 having a central aperture not shown coaxial with hole 22 a body portion 32 and a pair of parallel side walls 34 and 36 defining an area therebetween for storage of the lifting cords proceeding next to fig2 the arrangement of the devices in fig1 a and 1 b in a spring motor unit 40 is shown motor unit 40 includes a bracket having a planar back wall 42 onto which the storage drum 10 and output drum 20 are rotatably mounted in a spaced apart orientation axles 43 and 44 pass respectively through the apertures 12 and 22 of the drums 10 and 20 from fig2 it will be appreciated that output drum 20 is located adjacent wall 42 with the cord spool 30 located outwardly therefrom a consistent variable force spring is illustrated at 45 and is coupled between storage drum 10 and output drum 20 the spring itself will be described later the spring motor unit 40 also includes a pair of surfaces 46 and 47 which are parallel to one another and perpendicular to surface 42 defining a generally u shaped enclosure for the two drums and the cord spool a hole.