⚛️ Nickel Titanium alloy, or Nitinol, is known for its unique shape memory effect. To induce this, Nitinol is heated above 500 °C (932 °F) while held in a specific shape. With precise temperature control, timing, and quenching, it “remembers” this form. Once trained, Nitinol can be deformed at room temperature and will return to its original shape when reheated, typically near the boiling point of water.⁠ ⁠ In this demonstration, two Nitinol objects are shown: a wire trained to straighten and a spring trained to return to its coiled form. This behavior stems from a phase change between Martensite and Austenite crystal structures.⁠ ⁠ To build a Nitinol-based heat engine, a 0.5 mm-thick wire, trained to stay straight above 80 °C, is formed into a loop around two wheels of different sizes. When the smaller, lower wheel is partially submerged in hot water, the heated wire segment tries to straighten, creating tension. Uneven heating, imperfect geometry, and wheel shape create a torque imba...