Comment by aidenn0
5 years ago
Anything controlled by a PID can easily end up in a circular pattern, so it's not a given that this was to avoid stiction.
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1 dimensional PIDs can end up in a sinusoidal dynamic equilibrium, and a 2 dimensional sine wave is an ellipse.
It's not an ellipse if the axes have different periods: https://www.wolframalpha.com/input/?i=x%3Dsin%28t%29%2C+y%3D...
(Is there a name for this kind of curve?)