Methods, systems, and devices are provided that may include Stirling cycle configurations and/or linear-to-rotary mechanisms in accordance with various embodiments. Some embodiments include a Stirling cycle device that may include a first hot piston contained within a first hot cylinder and a first cold piston contained within a first cold cylinder. A first single actuator may be configured to couple the first hot piston with the first cold piston such that the first hot piston and the first cold piston are on different thermodynamic circuits. The different thermodynamic circuits may include adjacent thermodynamic circuits. The Stirling cycle configuration may be configured as a single-acting alpha Stirling cycle configuration. Some embodiments include a linear-to-rotary mechanism device. The device may include multiple linkages. The device may include a cam plate coupled with the multiple linkages utilizing a cam and multiple cam followers. The linkages may include Watt linkages.

An engine includes a compression chamber that intakes and compresses working fluid; an expansion chamber that expands and exhausts working fluid; and a transfer chamber that receives working fluid from the compression chamber and transfers working fluid to the expansion chamber, wherein an internal volume of the transfer chamber decreases during the transfer of working fluid.

A method of operating a thermodynamic apparatus configured as a heat engine or heat pump, the thermodynamic apparatus comprising, in flow series, a first heat exchanger, an expansion sub-chamber and a second heat exchanger, the method comprising transferring fluid from the first heat exchanger to the second heat exchanger via the expansion sub-chamber by: admitting a fluid flow at an intake pressure from the first heat exchanger into the expansion sub-chamber by increasing the volume of the expansion sub-chamber; fluidically isolating the fluid within the expansion sub-chamber from the first heat exchanger; expanding the fluid within the expansion sub-chamber by further increasing the volume of the expansion sub-chamber to reduce the pressure of the fluid from the intake pressure; fluidically coupling the expansion sub-chamber to the second heat exchanger; and transferring fluid out of the expansion sub-chamber to the second heat exchanger by reducing the volume of the expansion sub-chamber.