Abstract: An actuating mechanism for adjusting the swashplate angle in a Stirling cycle engine. A stationary mounted motor is used to drive one member of a planetary gear set. The motion of this member is transmitted through a second planetary gear set to a member connected to the swashplate. In one embodiment, a worm gear powered by a stationary mounted electric motor drives a moveable rear ring gear. The movement of the rear ring gear is transmitted through three rear planet gears and a common sun gear to produce relative movement in a front planet gear carrier. The relative movement of the front planet gear carrier is transmitted through a bevel gear to the swashplate. This embodiment allows the off-line production of swashplate actuator subassembly cartridges that can quickly be journalled to the drive shaft, joined to and properly phased with respect to the swashplate and meshed with a worm gear connected to the stationary electric motor during the assembly of a Stirling engine.