FixTheRobot Explore Robotics / Guidance, Navigation and Control / M6 / M6-L2

This lab works on phones, but writing code is much easier on a laptop.

Guidance, Navigation and Control · Inertial Navigation · M6-L2 · Advanced

Mechanize and Watch It Drift

Bench log · Hopper on the test range

17:40. Hopper stood on the pad with its engine off for two minutes, and its inertial position wandered by 50 metres. The sensors are within their datasheets. Nobody can say which of the two biases did it, or why the error grew faster at the end.

You will separate the two from the shape of the error, write the mechanization that produced it, and predict the drift from the biases alone.

Your task

    Simulation
    solution.pyLoading Python…
    Ctrl+Enter runs
    What Python can I use?

    Plain Python 3 with the standard library and the course library gnckit (import gnckit as g: transfer functions and margins, state space and LQR, the Hopper model, quaternions, a convex solver). NumPy is not available in the browser. Your code runs in a background worker: an endless loop is stopped after a few seconds and the page stays usable. It runs in your browser and is never sent anywhere.

    Hints

    What this lab teaches

    Stage 1: an accelerometer bias gives a position error that grows as t², a gyro bias as t³, because of the number of integrations; the two are separated by time. Stage 2: the planar mechanization: attitude from the gyro, the specific force rotated into the navigation frame and corrected for gravity, then velocity and position; a transposed rotation is invisible without a gyro bias. Stage 3: the closed-form error equations and the crossover time.

    Grading compares your final position with the reference to 1e-6 m, checks it against the error equations, and compares your predictions with the formulas on hidden biases.

    Theory for this lab

    Inertial Navigation labs

    1. M6-L1: Read the Allan Plot
    2. M6-L2: Mechanize and Watch It Drift: this lab.

    Educational simplification: a flat Earth, a single plane, a vehicle at rest and constant biases; Earth rotation, curvature and the Schuler oscillation are left out and matter after about ten minutes (module 6).

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