Control Systems — question 8 of 10
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You're tuning the P gain on a position control loop for a mechanical arm. As you raise the gain, steady-state tracking error shrinks nicely, but once gain crosses a certain threshold the arm starts buzzing — a small, persistent oscillation at roughly 40 Hz that wasn't there at lower gain, while gains just below that threshold were rock solid. Why does instability show up at one particular frequency rather than the system just getting generally jittery, and how would you use a frequency response measurement to find the actual cause before you decide how to fix it?