1. A clutch assembly for a roller door operator, the clutch assembly providing selective engagement between a motor and a door drive via a clutch assembly output drive shaft, the clutch assembly having a clutch base, a clutch cap and a clutch mechanism including one or more cam or ratchet elements arranged to rotate around the axis of said clutch assembly output drive shaft and configured to provide alternate engagement and disengagement between the motor and the clutch assembly output drive shaft with successive actuation and release actions of a clutch lever between a first position and a second position, the clutch assembly including a position encoder unit mountable to said clutch cap, the position encoder unit having a position encoder input shaft arranged to be driven directly by said clutch assembly output drive shaft, wherein said position encoder unit includes an absolute position encoder arranged to sense the rotational position of a magnetic element driven by rotation of the position encoder input shaft, configured such that 360° of rotation of the magnetic element corresponds to more than the full travel of a door driven by the roller door operator.