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Update example 13
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‎examples/CMakeLists.txt‎

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ADD_SUBDIRECTORY(example_10)
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ADD_SUBDIRECTORY(example_11)
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ADD_SUBDIRECTORY(example_12)
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ADD_SUBDIRECTORY(example_13)
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ADD_SUBDIRECTORY(example_14)
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ADD_SUBDIRECTORY(example_15)
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ADD_SUBDIRECTORY(example_16)

‎examples/example_11/example_11.cpp‎

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/*
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* This example shows how to create
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* a waypoint trajectory consisting of straight
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* lines
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*
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*
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*
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*/
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#include "bitrl/bitrl_config.h"
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#ifdef BITRL_CHRONO
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#include <chrono/physics/ChBodyEasy.h>
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#include <chrono_irrlicht/ChVisualSystemIrrlicht.h>
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#include "bitrl/utils/geometry/geom_point.h"
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#include "bitrl/utils/trajectory/line_segment_link.h"
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#include "bitrl/utils/trajectory/waypoint.h"
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#include "bitrl/utils/trajectory/waypoint_trajectory.h"
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#include "bitrl/utils/unit_converter.h"
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#include <any>
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#include <array>
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#include <iostream>
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#include <map>
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#include <string>
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#include <vector>
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namespace example_11
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{
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‎examples/example_11/example_11.md‎

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The main interface for creating rigid bodies in Chrono is the <a href="https://api.projectchrono.org/9.0.0/classchrono_1_1_ch_body.html">ChBody</a>
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class. You can also find this <a href="https://api.projectchrono.org/9.0.0/rigid_bodies.html"> Rigid Bodies</a> helpful.
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_ChBody_ is an abstract class, and therefore we cannot instantiate it directly. Chrono provides various classes however we can
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immediately use. The one we will use in this example is the _ChBodyEasyBox_ class. This is defined in the _<chrono/physics/ChBodyEasy.h>_ header.
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immediately use. The one we will use in this example is the _ChBodyEasyBox_ class. This is defined in the _chrono/physics/ChBodyEasy.h_ header.
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Let's first create a box and try to visualize it. Below is the function that constructs a box.
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@code{.cpp}

‎examples/example_13/CMakeLists.txt‎

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TARGET_LINK_LIBRARIES(${EXECUTABLE} PRIVATE bitrllib pthread boost_log)
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IF(ENABLE_CHRONO)
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TARGET_LINK_LIBRARIES(${EXECUTABLE} PRIVATE Chrono::Chrono_core)
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TARGET_LINK_LIBRARIES(${EXECUTABLE} PRIVATE Chrono::Chrono_core Chrono::Chrono_irrlicht)
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ENDIF ()
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IF(BITRL_WEBOTS)

‎examples/example_13/example_13.cpp‎

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#include "bitrl/bitrl_config.h"
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#ifdef BITRL_CHRONO
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#include "bitrl/bitrl_types.h"
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#include "bitrl/utils/geometry/geom_point.h"
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#include "bitrl/utils/geometry/mesh/mesh.h"
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#include "bitrl/utils/geometry/mesh/quad_mesh_generation.h"
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#ifdef BITRL_LOG
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#define BOOST_LOG_DYN_LINK
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#include <boost/log/trivial.hpp>
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#endif
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#include "chrono/core/ChRealtimeStep.h"
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#include "chrono/physics/ChSystemNSC.h"
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#include "chrono/physics/ChLinkMotorRotationSpeed.h"
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#include <chrono_irrlicht/ChVisualSystemIrrlicht.h>
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#include <filesystem>
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#include <iostream>
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namespace example_13
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{
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using namespace bitrl;
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using utils::geom::GeomPoint;
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using utils::geom::Mesh;
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using namespace chrono::irrlicht;
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// constants we will be using further below
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const uint_t WINDOW_HEIGHT = 800;
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const uint_t WINDOW_WIDTH = 1024;
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const real_t DT = 0.01;
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const real_t SIM_TIME = 5.0;
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const std::string WINDOW_TITLE( "Example 13");
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void prepare_visualization(chrono::irrlicht::ChVisualSystemIrrlicht& visual)
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{
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visual.SetWindowSize(WINDOW_WIDTH, WINDOW_WIDTH); //WINDOW_HEIGHT);
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visual.SetWindowTitle(WINDOW_TITLE);
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visual.Initialize();
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visual.AddLogo();
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visual.AddSkyBox();
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visual.AddCamera({0, -2, 1}, {0, 0, 0});
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visual.AddTypicalLights();
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visual.BindAll();
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}
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} // namespace example_13
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int main()
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{
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using namespace example_13;
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chrono::ChSystemNSC sys;
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sys.SetGravityY();
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try
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{
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// 2- Create the rigid bodies of the slider-crank mechanical system
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// (a crank, a rod, a truss), maybe setting position/mass/inertias of
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// their center of mass (COG) etc.
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// build a square grid
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Mesh<2> mesh;
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utils::geom::build_quad_mesh(mesh, 10, 10, GeomPoint<2>({0.0, 0.0}),
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GeomPoint<2>({1.0, 1.0}));
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// ..the truss
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auto my_body_A = chrono_types::make_shared<chrono::ChBody>();
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sys.AddBody(my_body_A);
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my_body_A->SetFixed(true); // truss does not move!
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my_body_A->SetName("Ground-Truss");
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std::cout << "Number of elements: " << mesh.n_elements() << std::endl;
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std::cout << "Number of nodes: " << mesh.n_nodes() << std::endl;
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}
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catch (std::exception &e)
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{
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std::cout << e.what() << std::endl;
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}
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catch (...)
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{
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// ..the crank
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auto my_body_B = chrono_types::make_shared<chrono::ChBody>();
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sys.AddBody(my_body_B);
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my_body_B->SetPos(chrono::ChVector3d(1, 0, 0)); // position of COG of crank
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my_body_B->SetMass(2);
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my_body_B->SetName("Crank");
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// ..the rod
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auto my_body_C = chrono_types::make_shared<chrono::ChBody>();
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sys.AddBody(my_body_C);
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my_body_C->SetPos(chrono::ChVector3d(4, 0, 0)); // position of COG of rod
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my_body_C->SetMass(3);
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my_body_C->SetName("Rod");
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// 3- Create constraints: the mechanical joints between the rigid bodies.
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// .. a revolute joint between crank and rod
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auto my_link_BC = chrono_types::make_shared<chrono::ChLinkLockRevolute>();
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my_link_BC->SetName("RevJointCrankRod");
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my_link_BC->Initialize(my_body_B, my_body_C, chrono::ChFrame<>(chrono::ChVector3d(2, 0, 0)));
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sys.AddLink(my_link_BC);
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// .. a slider joint between rod and truss
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auto my_link_CA = chrono_types::make_shared<chrono::ChLinkLockPointLine>();
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my_link_CA->SetName("TransJointRodGround");
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my_link_CA->Initialize(my_body_C, my_body_A, chrono::ChFrame<>(chrono::ChVector3d(6, 0, 0)));
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sys.AddLink(my_link_CA);
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std::cout << "Unknown exception occured" << std::endl;
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// .. a motor between crank and truss
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auto my_link_AB = chrono_types::make_shared<chrono::ChLinkMotorRotationSpeed>();
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my_link_AB->Initialize(my_body_A, my_body_B, chrono::ChFrame<>(chrono::ChVector3d(0, 0, 0)));
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my_link_AB->SetName("RotationalMotor");
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sys.AddLink(my_link_AB);
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auto my_speed_function = chrono_types::make_shared<chrono::ChFunctionConst>(chrono::CH_PI); // speed w=3.145 rad/sec
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my_link_AB->SetSpeedFunction(my_speed_function);
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chrono::irrlicht::ChVisualSystemIrrlicht visual;
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prepare_visualization(visual);
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visual.AttachSystem(&sys);
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// Simulation loop
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// Timer for enforcing soft real-time
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chrono::ChRealtimeStepTimer realtime_timer;
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// bool removed = false;
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while (visual.Run()) {
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// Irrlicht must prepare frame to draw
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visual.BeginScene();
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// Irrlicht now draws simple lines in 3D world representing a
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// skeleton of the mechanism, in this instant:
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//
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// .. draw items belonging to Irrlicht scene, if any
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visual.Render();
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// .. draw a grid
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tools::drawGrid(&visual, 0.5, 0.5);
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// .. draw GUI items belonging to Irrlicht screen, if any
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visual.GetGUIEnvironment()->drawAll();
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// .. draw the rod (from joint BC to joint CA)
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tools::drawSegment(&visual, my_link_BC->GetMarker1()->GetAbsCoordsys().pos,
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my_link_CA->GetMarker1()->GetAbsCoordsys().pos,
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chrono::ChColor(0, 1, 0));
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// .. draw the crank (from joint AB to joint BC)
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tools::drawSegment(&visual, my_link_AB->GetFrame2Abs().GetCoordsys().pos,
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my_link_BC->GetMarker1()->GetAbsCoordsys().pos,
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chrono::ChColor(1, 0, 0));
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// .. draw a small circle at crank origin
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tools::drawCircle(&visual, 0.1, chrono::ChCoordsys<>(chrono::ChVector3d(0, 0, 0), chrono::QUNIT));
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/* test: delete a link after 10 seconds
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if (sys.GetChTime() >10 && (!removed))
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{
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sys.RemoveLink(my_link_AB);
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removed = true;
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}*/
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// ADVANCE SYSTEM STATE BY ONE STEP
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sys.DoStepDynamics(DT);
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// Enforce soft real-time
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realtime_timer.Spin(DT);
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// Irrlicht must finish drawing the frame
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visual.EndScene();
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}
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return 0;
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}
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#else
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#include <iostream>
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int main()
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{
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std::cerr<<"You need PROJECTCHRONO configured with "
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<<"bitrl in order to run this example "
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<<"Reconfigure bitrl and set ENABLE_CHRONO=ON"<<std::endl;
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return 1;
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}
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#endif

‎examples/example_13/example_13.md‎

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\page bitrl_example_13 BitRL Example 13 Using chrono::ChSystemSMC
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Example \ref bitrl_example_11 discussed _ChBody_. Specifically, how to create a _ChBodyEasyBox_.
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Understanding rigid bodies is fundamental to robotics. In this example we will discuss _ChSystem_.
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This is the cornerstone of a Chrono simulation. Most information in this example
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can be found in the official doumentation here: <a href="https://api.projectchrono.org/9.0.0/simulation_system.html">Simulation system</a>.
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A _ChSystem_ is an abstract class. The Chrono library provides the following subclasses:
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- _ChSystemNSC_ for Non Smooth Contacts (NSC): in case of contacts a complementarity solver will take care of them using non-smooth dynamics; this is very efficient even with large time steps.
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- _ChSystemSMC_ for SMooth Contacts (SMC): contacts are handled using penalty methods, i.e. contacts are deformable
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Note that if there are no contacts or collisions in your system, it is indifferent to use _ChSystemNSC_ or _ChSystemSMC_.
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In this example we will create and simulate a differential drive system using Chrono
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@code{.cpp}
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@endcode
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