This is a very special kind of heat engine that demonstrates the conversion of heat into mechanical energy. It uses the unique property of Nitinol alloy (~50% Nickel, ~50% Titanium, the "nol" at the end of Nitinol refers to Naval Ordnance Laboratory in Maryland USA where this alloy was developed) called the "memory effect". Once Nitinol has been formed into shape at high temperature (about 600o C) and allowed to cool to room temperature, it can be easily deformed. However, when heated above a transition temperature (in this application about 50oC to 70o C) the Nitinol object abruptly returns to its high-temperature shape with substantially more force than that required to deform it when cold. Uses a Nitinol wire formed to a closed loop that drives the two connected wheels. Includes detailed instructions.