void testMcKibbenActuator()
{
double pressure = 5 * 10e5; // 5 bars
double num_turns = 1.5; // 1.5 turns
double B = 277.1 * 10e-4; // 277.1 mm
using namespace SimTK;
std::clock_t startTime = std::clock();
double mass = 1;
double ball_radius = 10e-6;
Model *model = new Model;
model->setGravity(Vec3(0));
Ground& ground = model->updGround();
McKibbenActuator *actuator = new McKibbenActuator("mckibben", num_turns, B);
OpenSim::Body* ball = new OpenSim::Body("ball", mass ,Vec3(0), mass*SimTK::Inertia::sphere(0.1));
ball->scale(Vec3(ball_radius), false);
actuator->addNewPathPoint("mck_ground", ground, Vec3(0));
actuator->addNewPathPoint("mck_ball", *ball, Vec3(ball_radius));
Vec3 locationInParent(0, ball_radius, 0), orientationInParent(0), locationInBody(0), orientationInBody(0);
SliderJoint *ballToGround = new SliderJoint("ballToGround", ground, locationInParent, orientationInParent, *ball, locationInBody, orientationInBody);
ballToGround->updCoordinate().setName("ball_d");
ballToGround->updCoordinate().setPrescribedFunction(LinearFunction(20 * 10e-4, 0.5 * 264.1 * 10e-4));
ballToGround->updCoordinate().set_prescribed(true);
model->addBody(ball);
model->addJoint(ballToGround);
model->addForce(actuator);
PrescribedController* controller = new PrescribedController();
controller->addActuator(*actuator);
controller->prescribeControlForActuator("mckibben", new Constant(pressure));
model->addController(controller);
ForceReporter* reporter = new ForceReporter(model);
model->addAnalysis(reporter);
SimTK::State& si = model->initSystem();
model->getMultibodySystem().realize(si, Stage::Position);
double final_t = 10.0;
double nsteps = 10;
double dt = final_t / nsteps;
RungeKuttaMersonIntegrator integrator(model->getMultibodySystem());
integrator.setAccuracy(1e-7);
Manager manager(*model, integrator);
manager.setInitialTime(0.0);
for (int i = 1; i <= nsteps; i++){
manager.setFinalTime(dt*i);
manager.integrate(si);
model->getMultibodySystem().realize(si, Stage::Velocity);
Vec3 pos;
model->updSimbodyEngine().getPosition(si, *ball, Vec3(0), pos);
double applied = actuator->computeActuation(si);;
double theoretical = (pressure / (4* pow(num_turns,2) * SimTK::Pi)) * (3*pow(pos(0), 2) - pow(B, 2));
ASSERT_EQUAL(applied, theoretical, 10.0);
manager.setInitialTime(dt*i);
}
std::cout << " ******** Test McKibbenActuator time = ********" <<
1.e3*(std::clock() - startTime) / CLOCKS_PER_SEC << "ms\n" << endl;
}
void testClutchedPathSpring()
{
using namespace SimTK;
// start timing
std::clock_t startTime = std::clock();
double mass = 1;
double stiffness = 100;
double dissipation = 0.3;
double start_h = 0.5;
//double ball_radius = 0.25;
//double omega = sqrt(stiffness/mass);
// Setup OpenSim model
Model* model = new Model;
model->setName("ClutchedPathSpringModel");
model->setGravity(gravity_vec);
//OpenSim bodies
const Ground* ground = &model->getGround();
// body that acts as the pulley that the path wraps over
OpenSim::Body* pulleyBody =
new OpenSim::Body("PulleyBody", mass ,Vec3(0), mass*Inertia::brick(0.1, 0.1, 0.1));
// body the path spring is connected to at both ends
OpenSim::Body* block =
new OpenSim::Body("block", mass ,Vec3(0), mass*Inertia::brick(0.2, 0.1, 0.1));
block->attachGeometry(new Brick(Vec3(0.2, 0.1, 0.1)));
block->scale(Vec3(0.2, 0.1, 0.1), false);
//double dh = mass*gravity_vec(1)/stiffness;
WrapCylinder* pulley = new WrapCylinder();
pulley->set_radius(0.1);
pulley->set_length(0.05);
// Add the wrap object to the body, which takes ownership of it
pulleyBody->addWrapObject(pulley);
// Add joints
WeldJoint* weld =
new WeldJoint("weld", *ground, Vec3(0, 1.0, 0), Vec3(0), *pulleyBody, Vec3(0), Vec3(0));
SliderJoint* slider =
new SliderJoint("slider", *ground, Vec3(0), Vec3(0,0,Pi/2),*block, Vec3(0), Vec3(0,0,Pi/2));
double positionRange[2] = {-10, 10};
// Rename coordinates for a slider joint
slider->updCoordinate().setName("block_h");
slider->updCoordinate().setRange(positionRange);
model->addBody(pulleyBody);
model->addJoint(weld);
model->addBody(block);
model->addJoint(slider);
ClutchedPathSpring* spring =
new ClutchedPathSpring("clutch_spring", stiffness, dissipation, 0.01);
spring->updGeometryPath().appendNewPathPoint("origin", *block, Vec3(-0.1, 0.0 ,0.0));
int N = 10;
for(int i=1; i<N; ++i){
double angle = i*Pi/N;
double x = 0.1*cos(angle);
double y = 0.1*sin(angle);
spring->updGeometryPath().appendNewPathPoint("", *pulleyBody, Vec3(-x, y ,0.0));
}
spring->updGeometryPath().appendNewPathPoint("insertion", *block, Vec3(0.1, 0.0 ,0.0));
// BUG in defining wrapping API requires that the Force containing the GeometryPath be
// connected to the model before the wrap can be added
model->addForce(spring);
PrescribedController* controller = new PrescribedController();
controller->addActuator(*spring);
// Control greater than 1 or less than 0 should be treated as 1 and 0 respectively.
double timePts[4] = {0.0, 5.0, 6.0, 10.0};
double clutchOnPts[4] = {1.5, -2.0, 0.5, 0.5};
PiecewiseConstantFunction* controlfunc =
new PiecewiseConstantFunction(4, timePts, clutchOnPts);
controller->prescribeControlForActuator("clutch_spring", controlfunc);
model->addController(controller);
model->print("ClutchedPathSpringModel.osim");
//Test deserialization
delete model;
model = new Model("ClutchedPathSpringModel.osim");
// Create the force reporter
ForceReporter* reporter = new ForceReporter(model);
model->addAnalysis(reporter);
model->setUseVisualizer(false);
SimTK::State& state = model->initSystem();
CoordinateSet& coords = model->updCoordinateSet();
coords[0].setValue(state, start_h);
model->getMultibodySystem().realize(state, Stage::Position );
//==========================================================================
// Compute the force and torque at the specified times.
RungeKuttaMersonIntegrator integrator(model->getMultibodySystem() );
integrator.setAccuracy(integ_accuracy);
Manager manager(*model, integrator);
manager.setWriteToStorage(true);
manager.setInitialTime(0.0);
double final_t = 4.99999;
manager.setFinalTime(final_t);
manager.integrate(state);
// tension is dynamics dependent because controls must be computed
model->getMultibodySystem().realize(state, Stage::Dynamics);
spring = dynamic_cast<ClutchedPathSpring*>(
&model->updForceSet().get("clutch_spring"));
// Now check that the force reported by spring
double model_force = spring->getTension(state);
double stretch0 = spring->getStretch(state);
// the tension should be half the weight of the block
double analytical_force = -0.5*(gravity_vec(1))*mass;
cout << "Tension is: " << model_force << " and should be: " << analytical_force << endl;
// error if the block does not reach equilibrium since spring is clamped
ASSERT_EQUAL(model_force, analytical_force, 10*integ_accuracy);
// unclamp and continue integrating
manager.setInitialTime(final_t);
final_t = 5.99999;
manager.setFinalTime(final_t);
manager.integrate(state);
// tension is dynamics dependent because controls must be computed
model->getMultibodySystem().realize(state, Stage::Dynamics);
// tension should go to zero quickly
model_force = spring->getTension(state);
cout << "Tension is: " << model_force << " and should be: 0.0" << endl;
// is unclamped and block should be in free-fall
ASSERT_EQUAL(model_force, 0.0, 10*integ_accuracy);
// spring is reclamped at 7s so keep integrating
manager.setInitialTime(final_t);
final_t = 10.0;
manager.setFinalTime(final_t);
manager.integrate(state);
// tension is dynamics dependent because controls must be computed
model->getMultibodySystem().realize(state, Stage::Dynamics);
// tension should build to support the block again
model_force = spring->getTension(state);
double stretch1 = spring->getStretch(state);
cout << "Tension is: " << model_force << " and should be: "<< analytical_force << endl;
// is unclamped and block should be in free-fall
ASSERT_EQUAL(model_force, analytical_force, 10*integ_accuracy);
cout << "Steady stretch at control = 1.0 is " << stretch0 << " m." << endl;
cout << "Steady stretch at control = 0.5 is " << stretch1 << " m." << endl;
ASSERT_EQUAL(2*stretch0, stretch1, 10*integ_accuracy);
manager.getStateStorage().print("clutched_path_spring_states.sto");
model->getControllerSet().printControlStorage("clutched_path_spring_controls.sto");
// Save the forces
reporter->getForceStorage().print("clutched_path_spring_forces.mot");
model->disownAllComponents();
cout << " ********** Test clutched spring time = ********** " <<
1.e3*(std::clock()-startTime)/CLOCKS_PER_SEC << "ms\n" << endl;
}
