1. Drive for the winding spindle of a curtain or roller blind having a wheel (7) which can be driven by means of a cord, is rotatably mounted in a housing (2), which is to be arranged in a stationary manner, and is connected through gearing by means of a planetary gear unit with a cam (14, 15) which can be mounted on the winding spindle (1) in a manner secure against rotation, with a helical spring brake (12), which rubs on a cylindrical surface (11) secure with respect to the housing and axially surrounds the cam (14, 15), preventing the cam (14, 15) from turning relative to the wheel (7) and with, further, an element (9) which turns with the wheel (7) interfering with the path of rotation of the cam (14, 15) and releasing the helical spring brake (12) upon rotation of the wheel (7), characterised in that the wheel (7) has an inner ring gear (8) which mates with at least one planet pinion (10) which is rotatably mounted on the plate-like element (9) axial to the wheel and which operates a ring gear (5) which is secure with respect to the housing, is concentric to the internally toothed ring gear (8) and is secure with respect to the housing (sic).
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