Abstract: Double epicyclic gear structure including a housing, a drive shaft rotatably mounted within the housing, first epicyclic gear structure mounted on the drive shaft, an input shaft connected to drive the first epicyclic gear structure, speed control structure connected to the sun gear of the first epicyclic gear structure for regulating the speed of rotation thereof, second epicyclic gear structure mounted on the drive shaft and engaged with the first epicyclic gear structure for rotation therewith, a brake band for stopping rotation of the planet gears of the second epicyclic gear structure and one-way clutch means mounting the ring gear of the second epicyclic gear structure on the drive shaft whereby on stopping of rotation of the planet gears about the drive shaft the drive shaft is driven in a forward direction, a brake band operable to prevent rotation of the ring gear of the second epicyclic gear structure and one-way clutch means mounting the planet gears for rotation on the drive shaft whereby on stopp