search

calcmogul / controls-engineering-in-frc

Controls Engineering in the FIRST Robotics Competition: Graduate-level control theory for high schoolers.
BSD 3-Clause "New" or "Revised" License
283 stars 25 forks source link

Why x not y #19

Closed SpencerGreene closed 2 years ago

SpencerGreene commented 2 years ago

Maybe a dumb question but in the PID section: https://github.com/calcmogul/controls-engineering-in-frc/blob/a76d9d7c5e4cfd653ee5640d5ee1e3a27c71cf87/fundamentals-of-control-theory/pid-controllers/derivative-term.tex#L62 the expansion is shown as e_k = r_k - x_k. Why isn't it e_k = r_k - y_k? The spring equation uses x but the control system example and diagram use y, am I missing something?

calcmogul commented 2 years ago

The state and output of the PID controller are equivalent in this context, but I'll modify it to use y for consistency.