Yuval Tassa
a264d0bc8b
https://youtu.be/GioWwB36XHI The new geom attribute adhesion (units of force, signed; pair-level override) translates the contact friction cone along its normal so that the force origin lies strictly inside it. Consequences: each contact can pull with up to the given force before breaking, and the tangential friction budget becomes mu*(f_N + adhesion) -- the Mohr-Coulomb yield condition with cohesion c = mu*adhesion -- so lightly-squeezed grasps retain a guaranteed friction floor. A translated cone factors exactly into {constant attractive force} + {original cone}, so no solver kernels change. The implementation is this factorization: a constant attraction along contact normals accumulated into the new mjData.qfrc_adhesion (summed into qfrc_passive), plus a bias of adhesive contact rows' reference acceleration (aref += R*adhesion), which makes resting penetration exactly independent of adhesion. Contacts of adhesive pairs remain active throughout the gap zone, producing rows with positive violation whose reference acceleration pulls: a tether that resists pull-off smoothly, captures objects released within the band into steady contact, and detaches at the specified force. Adhesion values of the two geoms combine by sum; explicit pairs override. mj_contactForce reports the net interface force (cone force minus the adhesive pull), whose normal component can now be negative. Negative adhesion is allowed and produces a repulsive offset (air hockey). PiperOrigin-RevId: 950858148 Change-Id: I879c08eba7ae501e5c0f8c2f807167344da4c2bc
114 lines
3.2 KiB
C++
114 lines
3.2 KiB
C++
// Copyright 2021 DeepMind Technologies Limited
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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// Tests for user/user_model.cc.
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#include <array>
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#include <cstddef>
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#include <string>
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#include <gmock/gmock.h>
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#include <gtest/gtest.h>
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#include <absl/strings/str_format.h>
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#include "src/cc/array_safety.h"
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#include <mujoco/mjdata.h>
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#include <mujoco/mjmodel.h>
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#include <mujoco/mujoco.h>
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#include "test/fixture.h"
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namespace mujoco {
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namespace {
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using ::testing::IsNull;
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using ::testing::NotNull;
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using ::testing::HasSubstr;
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using UserCompositeTest = MujocoTest;
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// ------------------------ cable tests ---------------------------------------
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TEST_F(UserCompositeTest, ShapeCanBeOmitted) {
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static constexpr char xml[] = R"(
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<mujoco>
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<worldbody>
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<composite type="cable" count="100 1 1" curve="s">
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<geom type="box" size="1 1 1"/>
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</composite>
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</worldbody>
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</mujoco>
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)";
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std::array<char, 1024> error;
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MjModelPtr m = LoadModelFromString(xml, error.data(), error.size());
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EXPECT_THAT(m.get(), NotNull()) << error.data();
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}
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TEST_F(UserCompositeTest, GeomSurfacevel) {
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static constexpr char xml[] = R"(
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<mujoco>
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<worldbody>
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<composite type="cable" count="5 1 1" curve="s">
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<geom type="capsule" size=".02" surfacevel="0 0 0 0 0 3"/>
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</composite>
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</worldbody>
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</mujoco>
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)";
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std::array<char, 1024> error;
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MjModelPtr m = LoadModelFromString(xml, error.data(), error.size());
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ASSERT_THAT(m.get(), NotNull()) << error.data();
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for (int g = 0; g < m->ngeom; g++) {
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if (m->geom_type[g] == mjGEOM_CAPSULE) {
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EXPECT_EQ(m->geom_surfacevel[6*g + 5], 3);
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}
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}
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}
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TEST_F(UserCompositeTest, GeomAdhesion) {
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static constexpr char xml[] = R"(
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<mujoco>
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<worldbody>
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<composite type="cable" count="5 1 1" curve="s">
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<geom type="capsule" size=".02" adhesion="2"/>
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</composite>
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</worldbody>
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</mujoco>
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)";
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std::array<char, 1024> error;
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MjModelPtr m = LoadModelFromString(xml, error.data(), error.size());
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ASSERT_THAT(m.get(), NotNull()) << error.data();
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for (int g = 0; g < m->ngeom; g++) {
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if (m->geom_type[g] == mjGEOM_CAPSULE) {
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EXPECT_EQ(m->geom_adhesion[g], 2);
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}
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}
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}
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TEST_F(UserCompositeTest, InvalidShape) {
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static constexpr char xml[] = R"(
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<mujoco>
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<worldbody>
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<composite type="cable" count="100 1 1" curve="s s exp">
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<geom type="box" size="1 1 1"/>
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</composite>
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</worldbody>
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</mujoco>
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)";
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std::array<char, 1024> error;
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MjModelPtr m = LoadModelFromString(xml, error.data(), error.size());
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EXPECT_THAT(m.get(), IsNull()) << error.data();
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EXPECT_THAT(error.data(),
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HasSubstr("The curve array contains an invalid shape"));
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}
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} // namespace
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} // namespace mujoco
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