Displaying parametric curves with virtual and physical tools

Parametric curves play an important role in mathematics and engineering education. The purpose of this paper is to introduce the hypotrochoid family of curves and to provide ideas and tools for teaching the topic. We give the general parametric equations of hypotrochoids and show that several special curves can be derived from these equations. To display the curves we use the Hypotrochoid Equation Tracer, which is a dynamic application made by Desmos graphic calculator. In addition we have created a LEGO robot called Spikograph, that models a Spirograph and draws different hypotrochoids providing a physical experience for students. Finally, we have compiled a student project to practice and deepen the knowledge about hypotrochoids.