T6RestLengthController.cpp

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/*
 * Copyright © 2012, United States Government, as represented by the
 * Administrator of the National Aeronautics and Space Administration.
 * All rights reserved.
 * 
 * The NASA Tensegrity Robotics Toolkit (NTRT) v1 platform is 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.
 */

// This module
#include "T6RestLengthController.h"
// This application
#include "T6Model.h"
// This library
#include "core/tgLinearString.h"
// The C++ Standard Library
#include <cassert>
#include <stdexcept>
#include <vector>

T6RestLengthController::T6RestLengthController(const double restLengthDiff) :
    m_restLengthDiff(restLengthDiff) 
{
    if (restLengthDiff < 0.0)
    {
        throw std::invalid_argument("You tried to push a rope!");
    }
}

void T6RestLengthController::onSetup(T6Model& subject)
{
    // Do a one-time update of all cable rest lengths
    // First, get all muscles (cables)
    const std::vector<tgLinearString*> muscles = subject.getAllMuscles();

    // then, iterate over all muscles
    for (size_t i = 0; i < muscles.size(); ++i)
    {
        tgLinearString * const pMuscle = muscles[i];
                assert(pMuscle != NULL);

                // set rest length of the i-th muscle
                // NOTE that we don't technically have a dt here: this is pre-simualtion.
                // However, the dt is only used in tgLinearString for upper-bounding
                // velocity and acceleration of our imaginary "motors," so we can
                // choose whatever we want here.
                double dt = 0.01;
                double desiredRestLength = pMuscle->getStartLength() - m_restLengthDiff;
                pMuscle->setRestLength(desiredRestLength, dt);
    }
}

// This method is included for now: this SHOULD really work without the update
// each timestep... but just including it in onSetup doesn't seem to work.
void T6RestLengthController::onStep(T6Model& subject, double dt)
{
    if (dt <= 0.0)
    {
        throw std::invalid_argument("dt is not positive");
    }
    else
    {
        // Do an update of all cable rest lengths
        // First, get all muscles (cables)
        const std::vector<tgLinearString*> muscles = subject.getAllMuscles();

                // then, iterate over all muscles
                for (size_t i = 0; i < muscles.size(); ++i)
                {
                    tgLinearString * const pMuscle = muscles[i];
                    assert(pMuscle != NULL);

                    // set rest length of the i-th muscle
                    double desiredRestLength = pMuscle->getStartLength() - m_restLengthDiff;
                    pMuscle->setRestLength(desiredRestLength, dt);
                }
    }
}