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Tires and roads

The tire element

type: tire puts a tire on body1, a wheel turning about its y axis (orient the wheel body accordingly). The contact is a point on the road below the wheel center, found every step on the road's tangent plane; the wheel may lift off.

forces:
  tire_fl:
    type: tire
    body1: wheel_fl
    radius: 0.31                  # unloaded radius
    tire: {kz: 250000, cz: 300}   # override defaults; see below

The built-in tire is a passenger car tire (roughly 205/55 R16) with vertical spring and damper, Magic Formula longitudinal and lateral forces with load dependence and combined slip, aligning moment and rolling resistance. Its coefficients can be overridden under tire::

r0 kz cz Fz0 Cx pDx1 pDx2 pEx1 pKx1 pKx3 Cy pDy1 pDy2 pEy1 pKy1 pKy2 rBx1 rBy1 t0 qBz qsy1 v_eps w_eps eps_z

Other tire models (complete Magic Formula data sets from .tir files, for instance) come as extensions: they add their keys to the tire and run on the same roads.

Channels: .force_x/y/z (longitudinal, lateral, vertical, in the contact frame), .slip0 (longitudinal slip), .slip1 (slip angle), .friction, .penetration, .contact_x/y/z, .road_height.

Roads

The road section is shared by all tires of a model.

A sum of up to 16 harmonic waves, a slope and a friction coefficient, with an optional patch of other friction (split-µ):

road:
  harmonics:
    - {amplitude: 0.01, wavelength: 20, heading: 0.0}
    - {amplitude: 0.003, wavelength: 2.5, heading: 0.4, phase: 1.2}
  slope: [0.0, 0.005]          # dh/dx, dh/dy
  friction: 1.0
  patch: {friction: 0.3, x: [60, 100], y: [0, 5], edge: 0.5}

road:
  crg: track.crg               # ASAM OpenCRG height grid
  crg_friction: track_mu.crg   # optional: a grid of friction coefficients
  friction: 1.0                # else a constant friction
  position: [0, 0, 0]          # placement of the CRG frame
  heading: 0.0

Read and evaluated with the official ASAM OpenCRG library: all data formats, curved reference lines, slope and banking, NaN values, border modes, modifiers, include files. A 2 km road on a 2 cm grid costs as much per step as a small one. freedyn2_road road.crg < points prints height, gradient and friction at points, to check a road and its placement.

key value
crg string OpenCRG file of the road height (relative to the model file): curved reference line, slope, banking.
crg_friction string OpenCRG file whose grid values are the friction coefficient (same placement as crg). Default: friction.
position list of 3 OpenCRG road: translation of the CRG frame in the world [m]. Default [0, 0, 0].
heading number OpenCRG road: rotation of the CRG frame about z [rad]. Default 0.
harmonics list
slope list of 2 [dh/dx, dh/dy]. Default [0, 0].
friction number mu0. Default 1.
patch object