Vamos Automotive Simulator git

//  A brake for a wheel.
//
//  Copyright (C) 2001-2019  Sam Varner
//
//  This file is part of Vamos Automotive Simulator.
//
//  Vamos is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  Vamos is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with Vamos.  If not, see <http://www.gnu.org/licenses/>.
//  along with this program; if not, write to the Free Software
//  Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

#include "Brake.hpp"
#include "../geometry/Numeric.hpp"

#include <cmath>

Vamos_Body::Brake::Brake(double sliding, double radius, double area, double max_pressure,
                         double bias)
    : m_friction(sliding),
      m_radius(radius),
      m_area(area),
      m_max_pressure(max_pressure * bias),
      m_bias(bias),
      m_threshold(4.0e-4),
      m_is_locked(false)
{
}

double Vamos_Body::Brake::torque(double factor, double rotational_speed)
{
    using Vamos_Geometry::sign;
    // `factor' is the fraction of maximum pressure applied.
    double pressure = factor * m_bias * m_max_pressure;
    double normal = pressure * m_area;
    double velocity = m_radius * rotational_speed;
    m_is_locked = std::abs(velocity) < m_threshold * normal;
    return m_is_locked ? 0.0 : m_friction * normal * m_radius * sign(velocity);
}