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Close planar moments at the KinPy contact positions #136

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Merged
rhorvath02 merged 1 commit into from
Oct 19, 2026
Merged

Close planar moments at the KinPy contact positions #136

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47 changes: 27 additions & 20 deletions engines/dynpy/models.py
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Original file line number Diff line number Diff line change
Expand Up @@ -265,6 +265,8 @@ def evaluate(
fx_body,
fy_body,
wheel_moments_body,
corner_positions,
suspension_forces,
)
closed_loads = np.maximum(
self._closed_normal_loads(
Expand Down Expand Up @@ -306,6 +308,8 @@ def evaluate(
fx_body,
fy_body,
wheel_moments_body,
corner_positions,
suspension_forces,
)
unsprung_accel = self._unsprung_acceleration_with_geometry(
unsprung_accel,
Expand Down Expand Up @@ -603,10 +607,12 @@ def _algebraic_load_transfer(
fx_body: FloatArray,
fy_body: FloatArray,
tire_moments_body: FloatArray,
corner_positions: FloatArray,
suspension_forces: FloatArray,
) -> FloatArray:
"""Return planar pitch/roll load transfer when suspension DOFs are absent."""

del fx_body, fy_body, tire_moments_body
del fx_body, fy_body, tire_moments_body, corner_positions, suspension_forces
return np.zeros(4)

def _unsprung_acceleration_with_geometry(
Expand Down Expand Up @@ -864,28 +870,29 @@ def _algebraic_load_transfer(
fx_body: FloatArray,
fy_body: FloatArray,
tire_moments_body: FloatArray,
corner_positions: FloatArray,
suspension_forces: FloatArray,
) -> FloatArray:
"""Close planar pitch and roll moments with contact-patch reactions."""

positions = self.parameters.corner_positions
front_x = float(np.mean(positions[:2, 0]))
rear_x = float(np.mean(positions[2:, 0]))
wheelbase = front_x - rear_x

# r x F gives My = z*Fx. Axle vertical reactions balance it.
horizontal_pitch_moment = float(np.sum(positions[:, 2] * fx_body + tire_moments_body[:, 1]))
front_delta = horizontal_pitch_moment / wheelbase
pitch_transfer = np.array(
[front_delta / 2.0, front_delta / 2.0, -front_delta / 2.0, -front_delta / 2.0]
)

# Tire lateral force gives Mx = -z*Fy. Roll stiffness splits the reaction by axle.
horizontal_roll_moment = float(np.sum(-positions[:, 2] * fy_body + tire_moments_body[:, 0]))
roll_transfer = self._roll_moment_load_transfer(
horizontal_roll_moment,
self._front_roll_stiffness_fraction(),
)
return pitch_transfer + roll_transfer
positions = corner_positions if self.dof == 3 else self.parameters.corner_positions
wheelbase = float(np.mean(positions[:2, 0]) - np.mean(positions[2:, 0]))
pitch_moment = float(np.sum(positions[:, 2] * fx_body + tire_moments_body[:, 1]))
roll_moment = float(np.sum(-positions[:, 2] * fy_body + tire_moments_body[:, 0]))
pitch_basis = np.array([0.5, 0.5, -0.5, -0.5]) / wheelbase
roll_basis = self._roll_moment_load_transfer(1.0, self._front_roll_stiffness_fraction())
if self.dof != 3:
return pitch_moment * pitch_basis + roll_moment * roll_basis

# The base weight/aero reactions were balanced at nominal contact positions.
offset = positions - self.parameters.corner_positions
pitch_moment -= float(np.dot(offset[:, 0], suspension_forces))
roll_moment += float(np.dot(offset[:, 1], suspension_forces))
roll_basis[:2] *= self.parameters.track_front_m / (positions[0, 1] - positions[1, 1])
roll_basis[2:] *= self.parameters.track_rear_m / (positions[2, 1] - positions[3, 1])
basis = np.column_stack((pitch_basis, roll_basis))
moments = np.vstack((positions[:, 1] @ basis, -positions[:, 0] @ basis))
return basis @ np.linalg.solve(moments, [-roll_moment, -pitch_moment])

def _front_roll_stiffness_fraction(self) -> float:
spring_rates = np.asarray(self.parameters.suspension_stiffness_n_per_m)
Expand Down
7 changes: 4 additions & 3 deletions tests/test_dyn_py.py
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Original file line number Diff line number Diff line change
Expand Up @@ -203,20 +203,21 @@ def test_component_cg_move_recomputes_total_cg_and_yaw_inertia(

@pytest.mark.parametrize("lateral_offset_m", [-0.10, 0.0, 0.10])
@pytest.mark.parametrize("speed_mps", [0.0, 12.0])
def test_3dof_balances_offset_cg_weight_and_roll_moment(tmp_path, lateral_offset_m, speed_mps):
@pytest.mark.parametrize("steering_rad", [-0.08, 0.0, 0.08])
def test_3dof_balances_offset_cg_weight_and_roll_moment(tmp_path, lateral_offset_m, speed_mps, steering_rad):
data = deepcopy(load_yaml(vehicle_yaml_path()))
data["driver_mass"]["cg_m"][1] += lateral_offset_m
path = tmp_path / "offset_driver.yml"
path.write_text(yaml.safe_dump(data), encoding="utf-8")
model = create_model(3, load_reduced_vehicle_parameters(path))
state = model.initial_state(speed_mps)
state[4] = 0.03 * speed_mps
output = model.evaluate(state)
output = model.evaluate(state, ModelInputs(steering_rad=steering_rad))

assert np.all(output.normal_loads_n > 0.0)
np.testing.assert_allclose(output.body_force_n[2], 0.0, atol=1e-6)
np.testing.assert_allclose(output.body_moment_nm[:2], 0.0, atol=1e-6)
if speed_mps == 0.0 and lateral_offset_m:
if speed_mps == 0.0 and lateral_offset_m and steering_rad == 0.0:
left_load = np.sum(output.normal_loads_n[[0, 2]])
right_load = np.sum(output.normal_loads_n[[1, 3]])
assert (left_load - right_load) * lateral_offset_m > 0.0
Expand Down
12 changes: 6 additions & 6 deletions tests/test_ggv_algebraic_validation.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,12 +17,12 @@ def vehicle():


@pytest.fixture(params=[
(3.0339375, [.08127771611779419, .011948983367535639, -1097.3395961433287],
[1099.5227144073162, 1148.0409699442903, 142.8844790676927, 203.82962748000404],
[-.06234121433735478, -.08241942768268194, -.07327790174822824, -.038537560917919066]),
(3.17184375, [.08600245137243437, .012545914587144966, -1083.6812622007656],
[1093.4686006166542, 1144.3284881569055, 146.29708187410307, 210.18362025164063],
[-.06068091266675208, -.08248753947971907, -.06433614520509952, -.03653756011222887]),
(3.0339375, [.0814769585661142, .011960084525452351, -1095.893672533613],
[1100.620281065146, 1144.8877103966538, 146.60676983627906, 202.16302960123133],
[-.0619017332585883, -.08267067604484639, -.06626921087274813, -.038846338906866444]),
(3.17184375, [.08607271034662606, .01254980413202482, -1082.3143524309924],
[1094.5665161798386, 1141.152659667364, 150.04883173700225, 208.50978331509785],
[-.06029758007249175, -.0827672664982325, -.06017286165229226, -.03681796283810693]),
])
def near_peak(vehicle, request):
ay, controls, loads, slips = request.param
Expand Down
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