Rhombic drive

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The rhombic drive is a specific method of transferring mechanical energy, or work, used almost exclusively when a single cylinder is used for two separately oscillating pistons.  A prime example of this use is on beta type-Stirling engines; the drive's complexity and tight tolerances causing a high cost of manufacture is a hurdle for the wide-spread usage of said engines.

In its simplest form, the drive utilizes a jointed rhomboid to convert linear work from a reciprocating piston to rotational work.  The connecting rod of the piston is rigid as opposed to a normal reciprocating engine which directly connects the piston to the crankshaft; instead, the rod connects to one corner of a rhombus.  When force is applied to the piston, it pushes down; at the same time, the outer corners of the rhomboid push out. An example of this type of motion is a cheap car jack, though in this case the work has been rotated 90 degrees. This transfers the work to a crank which rotates.

At this point, the linear reciprocating work of the piston has been converted to rotational work. The generator runs, the fan blows, or whatever else the piston has been enlisted to spin, spins.