test_mjcf_vel_ctrl.cpp

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/* test_mjcf_vel_ctrl.cpp
 * Joint velocity control on the Kinova GEN3 (MJCF).
 *
 * gen3.xml has high-gain position actuators (kp=2000, kv=100).
 * Velocity control is implemented in POSITION mode by integrating the
 * desired velocity into a position setpoint each step:
 *
 *   vel_des[i] = clamp(Kv * (target[i] - q[i]), -maxVel, maxVel)
 *   pos_cmd[i] += vel_des[i] * dt
 *
 * The position servo tracks the advancing setpoint, making the joint
 * follow the commanded velocity profile. */
 
#include "mj_kdl_wrapper/mj_kdl_wrapper.hpp"
 
#include <gtest/gtest.h>
 
#include <algorithm>
#include <cmath>
#include <filesystem>
#include <string>
 
static constexpr double kHomePose[7]   = { 0.0, 0.2618, 3.1416, -2.2689, 0.0, 0.9599, 1.5708 };
static constexpr double kTargetPose[7] = { 0.3, 0.5, 2.9, -2.0, 0.3, 1.2, 1.3 };
static constexpr double kKv            = 2.0;  // P gain [rad/s per rad error]
static constexpr double kMaxVel        = 0.6;  // velocity clamp [rad/s]
static constexpr double kTol           = 0.02; // convergence tolerance [rad]
static constexpr double kTimeout       = 5.0;  // max simulation time [s]
 
namespace fs = std::filesystem;
static fs::path repo_root() { return fs::path(__FILE__).parent_path().parent_path(); }
 
class MjcfVelCtrlTest : public testing::Test
{
  protected:
    fs::path      root_;
    mjModel      *model_ = nullptr;
    mjData       *data_  = nullptr;
    mj_kdl::Robot s_;
    unsigned      n_ = 0;
 
    void SetUp() override
    {
        root_ = repo_root();
        std::string arm_mjcf = (root_ / "third_party/menagerie/kinova_gen3/gen3.xml").string();
        if (!fs::exists(arm_mjcf)) {
            GTEST_SKIP() << arm_mjcf << " not found";
            return;
        }
 
        mj_kdl::SceneSpec sc;
        sc.robots.push_back(mj_kdl::RobotSpec{ .path = arm_mjcf.c_str(), .attachments = {} });
 
        ASSERT_TRUE(mj_kdl::build_scene(&model_, &data_, &sc));
        ASSERT_TRUE(mj_kdl::init_robot_from_mjcf(&s_, model_, data_, "base_link", "bracelet_link"));
 
        n_ = static_cast<unsigned>(s_.n_joints);
 
        KDL::JntArray q_home(n_);
        for (unsigned i = 0; i < n_; ++i) q_home(i) = kHomePose[i];
        mj_kdl::set_joint_pos(&s_, q_home);
 
        // POSITION mode: initialise pos_cmd to home so the servo starts settled.
        s_.ctrl_mode = mj_kdl::CtrlMode::POSITION;
        for (unsigned i = 0; i < n_; ++i) { s_.jnt_pos_cmd[i] = kHomePose[i]; }
        mj_kdl::update(&s_);
    }
 
    void TearDown() override
    {
        if (model_) {
            mj_kdl::cleanup(&s_);
            mj_kdl::destroy_scene(model_, data_);
        }
    }
};
 
TEST_F(MjcfVelCtrlTest, Convergence)
{
    const double dt      = model_->opt.timestep;
    bool         arrived = false;
 
    while (data_->time < kTimeout && !arrived) {
        mj_kdl::update(&s_); // reads sensors, applies prev pos_cmd to servo
 
        double max_err = 0.0;
        for (unsigned i = 0; i < n_; ++i) {
            double err = kTargetPose[i] - s_.jnt_pos_msr[i];
            max_err    = std::max(max_err, std::abs(err));
            double vel = std::clamp(kKv * err, -kMaxVel, kMaxVel);
            s_.jnt_pos_cmd[i] += vel * dt; // integrate velocity into position setpoint
        }
 
        if (max_err < kTol) {
            arrived = true;
            // Freeze setpoint at current position to avoid overshoot.
            for (unsigned i = 0; i < n_; ++i) s_.jnt_pos_cmd[i] = s_.jnt_pos_msr[i];
        }
 
        mj_kdl::step(&s_);
    }
 
    double max_err = 0.0;
    for (unsigned i = 0; i < n_; ++i)
        max_err = std::max(max_err, std::abs(kTargetPose[i] - s_.jnt_pos_msr[i]));
 
    EXPECT_TRUE(arrived) << "velocity controller did not converge within " << kTimeout << " s";
    EXPECT_LE(max_err, kTol * 2);
}
 
int main(int argc, char *argv[])
{
    testing::InitGoogleTest(&argc, argv);
    return RUN_ALL_TESTS();
}