Abstract: The SMA-CDS engine uses shape-memory-alloy (SMA) means which include at least one stack of conical-disc-springs (CDSs) mounted on a perforated tube. Each CDS has a zero axis, a martensite mode, and an austenite mode. A support structure mounts the CDSs on a tube so as to allow each CDS to reciprocate along the tube's outer wall and to deflect within a predetermined deflection range. A drive shaft is attached through a coupler to the stack of CDSS. Heating and cooling means cyclically heat and cool the stack of CDSs thereby causing each CDS thereof to cyclically transform in response to the heating from its said martensite mode into its said austenite mode, and in response to the cooling to return to its said martensite mode, and during each such transformation cycle each CDS deflects within the predetermined deflection range and generates martensite deflection forces and austenite extension forces of different magnitudes which result in a resultant force that causes the drive shaft to reciprocate.