Control Systems — question 4 of 10
Write a real answer. It is graded against the question's rubric, and the mastery movement is computed by the same engine the product uses. Scoring here is deterministic rather than model-written, so this page costs nothing to run and nothing is saved. In a track built from your own posting, the same rubric is graded by the model, which is what produces feedback about your reasoning rather than about coverage.
Use the rule of thumb that a pure time delay T contributes roughly 90 degrees of phase lag at f = 1/(4T), and you want to keep crossover safely below that frequency to preserve phase margin.
A motor position loop runs its control update at 100 Hz. The encoder-to-controller communication and the motor driver's response together add roughly 15ms of pure delay before a commanded change actually affects position. If you want the closed loop's crossover frequency (roughly where gain margin starts to erode) to stay comfortably below the frequency where this delay eats your phase margin, about how fast, in Hz, would you want the loop's bandwidth to stay under, using the rule that 15ms of delay costs about 90 degrees of phase at f = 1/(4*delay)?
This one resolves to a number. Give the value in the field below and your reasoning in the box — the number is checked exactly, by arithmetic.