tgSpringCable.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 "tgSpringCable.h"
#include "tgSpringCableAnchor.h"

#include <iostream>
#include <stdexcept>
#include <cassert>

tgSpringCable::tgSpringCable( const std::vector<tgSpringCableAnchor*>& anchors,
                                                                double coefK,
                                                                double dampingCoefficient,
                                                                double pretension) :
m_damping(0.0),
m_velocity(0.0),
m_coefK (coefK),
m_dampingCoefficient(dampingCoefficient)
{
                // Anchors will be stored in child classes
                assert(anchors.size() >= 2);
                assert(coefK > 0.0);
                assert(dampingCoefficient >= 0.0);
                
                std::size_t n = anchors.size();
                
                btVector3 pos1 = anchors[0]->getWorldPosition();
                btVector3 pos2 = anchors[n - 1]->getWorldPosition();
                
                m_restLength = pos1.distance(pos2) - pretension / coefK;
                
                if (m_restLength <= 0.0)
                {
                                throw std::invalid_argument("Pretension causes string to shorten past rest length!");
                }
                
                m_prevLength = m_restLength;
}

tgSpringCable::~tgSpringCable()
{
}

const double tgSpringCable::getRestLength() const
{
    return m_restLength;
}

void tgSpringCable::setRestLength( const double newRestLength)
{
    // Assume we've already put this through a motor model
    // But check anyway
    assert(newRestLength > 0.0);
    
    m_restLength = newRestLength;
}