The invention refers to a motor mechanism (6) for a drug delivery device (1), comprising a storage drum (8) and a torque drum (9) arranged close to each other and a strip (7) of spring sheet metal having two ends, each end attached to one of the drums (8, 9), wherein the strip (7) of spring sheet metal is coiled on the storage drum (8) in a relaxed state, wherein the motor mechanism (6) Is chargeable by rotating the torque drum (9) thereby coiling the strip (7) of spring sheet metal onto the torque drum (9) and bending the strip (7) of spring sheet metal the other way round than in the relaxed state thus arriving in a charged state with the strip (7) of spring sheet metal tending to re-coil onto the storage drum (8) thereby generating a torque. Fig. 2A
