## 20 March 2018

### Spirograph

The spirograph produces a variety of mathematical curves known technically as hypotrochoid and epitrochoid.

The spirograph was designed by Bruno Abakanowicz but as a toy was developed by the British engineer Denys Fisher, who exhibited it at the $1965$ Nuremberg International Toy Fair, and later being produced by his company.

The spirograph is constituted by a set of plastic pieces of various shapes such as rings, triangles or straight bars. There are several sizes of pieces and shapes, and all the edges have gear teeth to engage any other piece. You must have a sheet of paper which is placed on a cardboard backing. One of the pieces (the stator) is secured with pins on the paper and on the cardboard. Another piece (the rotor) is placed so that its teeth engage with those of the pinned piece. The point of a pen is placed in a hole on the rotor. When it is displaced, the pen traces a curve. There are many possible combinations.