Abstract: Disclosed is an automatically variable transmission of the planetary type in which the planet gears of the main or power gear train are carried on a rotatable power cage but are not bounded by an internally toothed ring gear. The transmitted torque and speed (relative to input speed) are functions of the rate of rotation of the power cage. Power cage rotation is controlled by driving it through a second or control planetary gear train having a similar rotatable control cage, the source of power being the input shaft of the transmission. The speed ratio of the main gear train decreases from input to output, while that of the control gear train increases. In operation, the rotational speeds of the power cage and the control cage adjust automatically upon variations in load to values appropriate for delivery of the amount of torque required at the required speed.