data/validation/README.md

Validation data

Single-wheel testbed data digitised from published papers. Used only to validate the evaluator; never used for training the surrogate.

Active reference grids

• wong_layer3_reference.csv — Layer-3 BW-vs-published reference grid exercised by tests/test_terramechanics.py::test_layer3_published_reference_grid. Each row is one (wheel, soil, vertical load, slip) operating point with per-quantity [lo, hi] tolerance bands. Three row kinds:

  1. characterisation — Wong (2008) §4.2-style worked-example fixture (JSC-1A canonical Bekker parameters; R=0.10 m, b=0.06 m; 50 N at slip ∈ {0.05, 0.20, 0.50}). Bounds pinned at the BW kernel's verified outputs to within ±5 % so the test guards against unintended kernel drift while staying inside the ±15-30 % BW model-form band reported in the literature.
  2. published_rover_class — Apollo nominal regolith × a smooth Pragyan-class wheel (R=0.135 m, b=0.10 m, W=70.2 N) and a grousered Yutu-2-class wheel (R=0.165 m, b=0.150 m, h_g=0.012 m, N_g=14, W=36.4 N). Bounds sized at the published Bekker-Wong model-form error (Ishigami 2007; Ding et al. 2011).
  3. closed_form_limit — kernel regression checks at analytic limits (e.g. smooth wheel with N_g>0 ⇒ grouser lift factor ≡ 1; bounds pinned at the v1 kernel output, not digitised experiments).

  Appending rows is additive — the test reads the CSV with csv.DictReader and parametrises one case per row.

• single_wheel_experiments.csv — experiment-vs-model worksheet for the experimental anchor of Layer 3. Each row is one measured single-wheel operating point: wheel geometry, vertical load, slip, the soil simulant name (Bekker parameters resolved from ../soil_simulants.csv), and the Janosi-Hanamoto shear modulus soil_shear_modulus_k_m. The meas_drawbar_pull_n / meas_sinkage_m / meas_torque_nm columns hold point measurements traced from the source figures.

  Consumed by roverdevkit.validation.terramechanics_experiment (compare_to_experiment, summarise) and tests/test_terramechanics_experiment.py. The harness runs the analytical Bekker-Wong kernel at every operating point and reports residuals + percentage errors against the measured columns. scripts/make_terramechanics_experiment_figure.py renders the terramechanics-experiment figure (reports/figures/fig_terramechanics_experiment.png) from it.

Sources

• Ding et al. 2011, J. Terramechanics 48(1):27-45 — rigid single-wheel slip/sinkage/drawbar-pull experiments (R=135/157 mm, b=110/165 mm, lugs 0-15 mm, loads 30/80/150 N, slip 0-0.6). Digitised from Fig. 8/9 (Wh3 family: Wh34 smooth + Wh32 grousered at 80 N; soil Bekker params from Table 2 → Ding2011_planetary_simulant in ../soil_simulants.csv). BW reproduces drawbar pull within the literature model-form band (~27 % median |error|).
• Wang & Han 2016, J. Korean Geotech. Soc. 32(11):97-108 (open access) — KLS-1 single-wheel testbed (R=85 mm, b=80 mm, 59 N), smooth vs grousered (h=10 mm), slip 0.1-0.5. Digitised from Fig. 14. The paper publishes only shear strength (Table 2: C=1.716 kPa, φ=40.6°); the pressure-sinkage moduli in KLS-1 (../soil_simulants.csv) are KLS-1's own bevameter-measured Bekker values (Lim et al. 2021, J. Astron. Space Sci. 38(4):237; n=1.2594, k_c=-44.06, k_phi=3581.8). This is a deliberate stress case at the edge of the rigid-wheel kernel's regime: the smallest/most-lightly-loaded wheel on a firm, dense, fines-rich simulant that barely sinks (1-14 mm), so BW's force-balance sinkage solve over-predicts DP and sinkage (~135 % / ~385 % median |error|) and cannot capture the measured DP collapse at s≈0.5.
• Hurrell et al. 2025, Space Sci. Rev. 221 art. 37 (open access, CC-BY) — Rashid-1 micro-rover wheel (R=100 mm, b=80 mm, 14 grousers h=20 mm, 24.5 N) on FJS-1, slip 0.1-0.5. Digitised from Figs. 5/6: meas_drawbar_pull_n = traction coefficient F_x/F_z (Fig. 5) × 24.5 N; meas_sinkage_m from Fig. 6; torque not reported. Soil = Hurrell2025_FJS1 (../soil_simulants.csv): cohesion 2.4 kPa (Ozaki et al. 2023) and AoR 38°, pressure-sinkage proxied from catalogue FJS-1. Most application-relevant case (in-scope micro-rover wheel + load); BW lands within band on both DP (24 % median) and sinkage (28 %).
• Iizuka & Kubota 2011 — grousered-wheel experiments motivating the arc-density grouser correction (not digitised into this grid; empirical grousered-wheel checks live in single_wheel_experiments.csv).
• Wong — datasets from Theory of Ground Vehicles (4th ed.) ch. 4.

Keep raw digitised traces in raw/ (git-ignored, re-downloadable from the papers); curated, checked-in reference rows live in wong_layer3_reference.csv / single_wheel_experiments.csv at this level.