quadrotor_decoupled_6d.h

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/*
 * Copyright (c) 2017, The Regents of the University of California (Regents).
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 *    2. Redistributions in binary form must reproduce the above
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 *       contributors may be used to endorse or promote products derived
 *       from this software without specific prior written permission.
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 * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS AS IS
 * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
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 * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
 * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
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 * Please contact the author(s) of this library if you have any questions.
 * Authors: David Fridovich-Keil   ( dfk@eecs.berkeley.edu )
 */

//
// Defines the QuadrotorDecoupled6D class, which uses PositionVelocity as the
// state and QuadrotorControl as the control, and models the dynamics as a
// three decoupled 2D systems.
//

#ifndef FASTRACK_DYNAMICS_QUADROTOR_DECOUPLED_6D_H
#define FASTRACK_DYNAMICS_QUADROTOR_DECOUPLED_6D_H

#include <fastrack/control/quadrotor_control.h>
#include <fastrack/control/quadrotor_control_bound_box.h>
#include <fastrack/dynamics/dynamics.h>
#include <fastrack/state/position_velocity.h>

#include <math.h>

namespace fastrack {
namespace dynamics {

using control::QuadrotorControl;
using control::QuadrotorControlBoundBox;
using state::PositionVelocity;

template <typename CB>
class QuadrotorDecoupled6D
  : public Dynamics<PositionVelocity, QuadrotorControl, CB, Empty> {
 public:
  ~QuadrotorDecoupled6D() {}
  explicit QuadrotorDecoupled6D()
    : Dynamics<PositionVelocity, QuadrotorControl, CB, Empty>() {}
  explicit QuadrotorDecoupled6D(const CB& bound)
    : Dynamics<PositionVelocity, QuadrotorControl, CB, Empty>(bound) {}
  explicit QuadrotorDecoupled6D(const std::vector<double>& params)
    : Dynamics<PositionVelocity, QuadrotorControl, CB, Empty>(params) {}

  // Derived classes must be able to give the time derivative of state
  // as a function of current state and control.
  inline PositionVelocity Evaluate(const PositionVelocity &x,
                                   const QuadrotorControl &u) const {
    // Position derivatives are just velocity.
    const Vector3d position_dot(x.Velocity());

    // Velocity derivatives are given by simple trigonometric functions
    // of the pitch/roll, scaled by G since we assume that thrust is
    // approximately equal to G.
    const Vector3d velocity_dot(constants::G * std::tan(u.pitch),
                                -constants::G * std::tan(u.roll),
                                u.thrust - constants::G);

    return PositionVelocity(position_dot, velocity_dot);
  }

  // Derived classes must be able to compute an optimal control given
  // the gradient of the value function at the specified state.
  // In this case (linear dynamics), the state is irrelevant given the
  // gradient of the value function at that state.
  inline QuadrotorControl OptimalControl(
      const PositionVelocity &x, const PositionVelocity &value_gradient) const {
    // Check initialization.
    if (!this->control_bound_)
      throw std::runtime_error(
          "QuadrotorDecoupled6D: uninitialized call to OptimalControl.");

    // Map the negative value gradient's control coefficients to
    // QuadrotorControl, so we get a negative gradient.
    QuadrotorControl negative_grad;
    negative_grad.yaw_rate = 0.0;
    negative_grad.pitch = -value_gradient.Vx();
    negative_grad.roll = value_gradient.Vy();
    negative_grad.thrust = -value_gradient.Vz();

    // Project onto control bound and make sure to zero out yaw_rate.
    QuadrotorControl c = this->control_bound_->ProjectToSurface(negative_grad);
    c.yaw_rate = 0.0;

    return c;
  }

  // Convert to the appropriate service response type.
  inline Empty ToRos() const {
    throw std::runtime_error("QuadrotorDecoupled6D: ToRos is unimplemented.");
    return Empty();
  }

  // Convert from the appropriate service response type.
  inline void FromRos(const Empty &res) {
    throw std::runtime_error("QuadrotorDecoupled6D: FromRos is unimplemented.");
  }

};  //\class QuadrotorDecoupled6D

}  // namespace dynamics
}  // namespace fastrack

#endif