# Definition:Epicycloid/Generator/Rotor

## Definition

Let an epicycloid be generated by rolling a circle $C_1$ around the outside of another circle $C_2$.

The circle $C_1$ can be referred to as the rotor of the epicycloid.

## Note on Terminology

The term rotor as used in this context appears to be non-standard.

The term has been taken by $\mathsf{Pr} \infty \mathsf{fWiki}$ from the children's toy Spirograph, which itself was taken from the term rotor as applied to the moving (rotating) part of a a rotary machine.

While the literature on epicycloids is extensive, there appears from some cursory web searching that there does not appear to be a standard name for either of the circles involved in their generation.

As the philosophy of $\mathsf{Pr} \infty \mathsf{fWiki}$ values brevity, it has been decided that this can be remedied.