A medical delivery device for advancing a piston in a medicament container to expel a medicament. A support structure supports the container and a drive assembly that advances the piston. The drive assembly includes a drive ribbon that can be retracted and extended. The retracted ribbon defines a spiral and the extended ribbon defines a helix. The drive ribbon is incrementally moveable between the retracted spiral configuration and extended helical configuration. A mechanical drive rotates the drive ribbon to selectively extend and retract the ribbon. A thrust member having a helical ramp engages a proximal edge of the drive ribbon where it transitions between a spiral and helix. A bearing member at the distal end of the drive ribbon exerts an axial force on the piston when the ribbon is extended.
