A drive arrangement comprises a support arm 26 pivotally mounted to a support structure 18, a drive mechanism 24 mounted upon the support arm 26 at a fixed position along the length thereof, the drive mechanism 24 having a drive output, and an output shaft 30 connected to the drive output by way of a universal joint 28. Preferably the arrangement is used for opening vents on polytunnels or greenhouses wherein the support structure carries a flap of flexible material and a roller tube is connected to a free end of the flap and the drive arrangement is operable to drive the roller tube for rotation
