Definition:Hypocycloid/Generator/Rotor

Definition
Let a hypocycloid be generated by rolling circle $C_1$ around the inside of another (larger) circle $C_2$.


 * Hypocycloid.png

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

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

The term has been taken by 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 hypocycloids 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 values brevity, it has been decided that this can be remedied.