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Prevent degenerate body inverse weights in constraints.

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Fixes #2472

PiperOrigin-RevId: 855223971
Change-Id: I646207f82353b7099aab9e220888fe11a4cd3d6d
This commit is contained in:
Yuval Tassa
2026-01-12 07:42:18 -08:00
committed by Copybara-Service
parent f0e1d8ce2c
commit 1cda1e7a8c
2 changed files with 49 additions and 2 deletions
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src/engine/engine_setconst.c
+12 -2
View File
@@ -376,8 +376,18 @@ static void set0(mjModel* m, mjData* d) {
}
// average diagonal and assign
m->body_invweight0[2*i] = (A[0] + A[7] + A[14])/3;
m->body_invweight0[2*i+1] = (A[21] + A[28] + A[35])/3;
mjtNum tran = (A[0] + A[7] + A[14])/3;
mjtNum rot = (A[21] + A[28] + A[35])/3;
// if one is zero, use the other to prevent degenerate constraints
if (tran < mjMINVAL && rot > mjMINVAL) {
tran = rot; // use rotation as fallback for translation
} else if (rot < mjMINVAL && tran > mjMINVAL) {
rot = tran; // use translation as fallback for rotation
}
m->body_invweight0[2*i] = tran;
m->body_invweight0[2*i+1] = rot;
}
}
test/engine/engine_forward_test.cc
+37
View File
@@ -810,6 +810,43 @@ TEST_F(ForwardTest, MocapQuats) {
mj_deleteModel(model);
}
// model with degenerate translational inertia
TEST_F(ForwardTest, DegenerateInertia) {
static constexpr char xml[] = R"(
<mujoco>
<option integrator="implicitfast" cone="elliptic">
<flag gravity="disable"/>
</option>
<worldbody>
<body name="1" pos="0.05 0.3 0">
<joint name="1" axis="0 1 0"/>
<geom type="capsule" size="0.1 0.5"/>
</body>
<body name="2">
<joint name="2" axis="1 0 0" stiffness="1" springref="90"/>
<geom type="capsule" size="0.1 0.5"/>
</body>
</worldbody>
</mujoco>
)";
char error[1024];
mjModel* model = LoadModelFromString(xml, error, sizeof(error));
ASSERT_THAT(model, NotNull()) << error;
mjData* data = mj_makeData(model);
for (int i = 0; i < 1000; i++) {
mj_step(model, data);
EXPECT_EQ(data->warning[mjWARN_BADQACC].number, 0)
<< "divergence at timestep " << i;
if (data->warning[mjWARN_BADQACC].number != 0) {
break;
}
}
mj_deleteData(data);
mj_deleteModel(model);
}
// user defined 2nd-order activation dynamics: frequency-controlled oscillator
// note that scalar mjcb_act_dyn callbacks are expected to return act_dot, but
// since we have a vector output we write into act_dot directly