exampleSlidingMass.py

This is Moco's simplest example.

# -------------------------------------------------------------------------- #
# OpenSim Moco: exampleSlidingMass.py                                        #
# -------------------------------------------------------------------------- #
# Copyright (c) 2017 Stanford University and the Authors                     #
#                                                                            #
# Author(s): Christopher Dembia                                              #
#                                                                            #
# Licensed under the Apache License, Version 2.0 (the "License"); you may    #
# not use this file except in compliance with the License. You may obtain a  #
# copy of the License at http://www.apache.org/licenses/LICENSE-2.0          #
#                                                                            #
# Unless required by applicable law or agreed to in writing, software        #
# distributed under the License is distributed on an "AS IS" BASIS,          #
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.   #
# See the License for the specific language governing permissions and        #
# limitations under the License.                                             #
# -------------------------------------------------------------------------- #

import os
import opensim as osim

model = osim.Model()
model.setName('sliding_mass')
model.set_gravity(osim.Vec3(0, 0, 0))
body = osim.Body('body', 2.0, osim.Vec3(0), osim.Inertia(0))
model.addComponent(body)

# Allows translation along x.
joint = osim.SliderJoint('slider', model.getGround(), body)
coord = joint.updCoordinate()
coord.setName('position')
model.addComponent(joint)

actu = osim.CoordinateActuator()
actu.setCoordinate(coord)
actu.setName('actuator')
actu.setOptimalForce(1)
model.addComponent(actu)

body.attachGeometry(osim.Sphere(0.05))

model.finalizeConnections()

# Create MocoStudy.
# ================
study = osim.MocoStudy()
study.setName('sliding_mass')

# Define the optimal control problem.
# ===================================
problem = study.updProblem()

# Model (dynamics).
# -----------------
problem.setModel(model)

# Bounds.
# -------
# Initial time must be 0, final time can be within [0, 5].
problem.setTimeBounds(osim.MocoInitialBounds(0.), osim.MocoFinalBounds(0., 5.))

# Position must be within [-5, 5] throughout the motion.
# Initial position must be 0, final position must be 1.
problem.setStateInfo('/slider/position/value', osim.MocoBounds(-5, 5),
                     osim.MocoInitialBounds(0), osim.MocoFinalBounds(1))
# Speed must be within [-50, 50] throughout the motion.
# Initial and final speed must be 0. Use compact syntax.
problem.setStateInfo('/slider/position/speed', [-50, 50], [0], [0])

# Applied force must be between -50 and 50.
problem.setControlInfo('/actuator', osim.MocoBounds(-50, 50))

# Cost.
# -----
problem.addGoal(osim.MocoFinalTimeGoal())

# Configure the solver.
# =====================
solver = study.initCasADiSolver()
solver.set_num_mesh_intervals(100)

# Now that we've finished setting up the study, print it to a file.
study.printToXML('sliding_mass.omoco')

# Solve the problem.
# ==================
solution = study.solve()

solution.write('sliding_mass_solution.sto')

if os.getenv('OPENSIM_USE_VISUALIZER') != '0':
    study.visualize(solution);