FixTheRobot Explore Robotics / Guidance, Navigation and Control / M6 / M6-L1

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Guidance, Navigation and Control · Inertial Navigation · M6-L1 · Intermediate

Read the Allan Plot

Bench log · Hopper on the test range

08:20. Three gyros arrived for Hopper's heading, a cheap one, an industrial one and a tactical one, and the purchasing office wants the cheapest that meets the requirement. Each was logged at rest for an hour. The datasheets quote different numbers in different units.

You will compute the Allan deviation of the logs, read the noise coefficients off the plot, and choose.

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: how to read an Allan plot: white noise falls with slope −1/2, the bias instability is the flat floor, and the rate random walk rises; the drift after ten minutes depends on the floor, not on the noise at one second. Stage 2: computing the overlapping Allan deviation from a record, with the factor 2 of the definition. Stage 3: reading the three coefficients, including the 0.664 of the flicker floor.

    Grading compares your Allan deviation and your coefficients with the reference to 1e-9 on hidden records, and checks that the gyro you choose meets the requirement.

    Theory for this lab

    Inertial Navigation labs

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

    Educational simplification: one axis, three noise processes at 1 Hz sampling, and a drift model that adds the angle random walk and a worst-case bias instability. Real gyros also have temperature effects, scale-factor errors and quantization (module 6).

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