AirBrakesPI.cpp

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/* Copyright (c) 2021-2022 Skyward Experimental Rocketry
 * Authors: Vincenzo Santomarco, Alberto Nidasio, Emilio Corigliano
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */
 
#include "AirBrakesPI.h"
 
#include <logger/Logger.h>
#include <math.h>
#include <utils/Constants.h>
 
#include <limits>
 
#include "drivers/timer/TimestampTimer.h"
#include "utils/Debug.h"
 
using namespace std;
 
namespace Boardcore
{
 
AirBrakesPI::AirBrakesPI(
    std::function<TimedTrajectoryPoint()> getCurrentPosition,
    const TrajectorySet& trajectorySet, const AirBrakesPIConfig& config,
    std::function<void(float)> setActuator)
    : getCurrentPosition(getCurrentPosition), config(config),
      setActuator(setActuator), pi(config.KP, config.KI, config.TS),
      trajectorySet(trajectorySet)
{
}
 
bool AirBrakesPI::init() { return true; }
 
void AirBrakesPI::begin()
{
    if (running)
        return;
 
    lastPosition = getCurrentPosition();
    chooseTrajectory(lastPosition);
    Algorithm::begin();
}
 
void AirBrakesPI::step()
{
    auto currentPosition = getCurrentPosition();
 
    // Do nothing if we have no new data
    if (lastPosition.timestamp >= currentPosition.timestamp)
        return;
 
    lastPosition = currentPosition;
 
    auto setPoint = getSetpoint(currentPosition);
    float rho     = getRho(currentPosition.z);
 
    float targetDrag = piStep(currentPosition, setPoint, rho);
    float surface    = getSurface(currentPosition, rho, targetDrag);
    setActuator(surface / config.SURFACE);
}
 
float AirBrakesPI::getRho(float z)
{
    return Constants::RHO_0 * expf(-z / Constants::Hn);
}
 
float AirBrakesPI::getSurface(const TimedTrajectoryPoint& currentPosition,
                              float rho, float targetDrag)
{
    float bestDDrag   = numeric_limits<float>::infinity();
    float bestSurface = 0;
 
    // TODO: Drags are monotone, here the algorithm can be more efficient
    for (uint8_t step = 0; step < config.DRAG_STEPS; step++)
    {
        float surface = (step / (config.DRAG_STEPS - 1)) * config.SURFACE;
 
        float extension = getExtension(surface);
        float cd        = getCD(currentPosition, extension);
        float drag      = getDrag(currentPosition, cd, rho);
        float dDrag     = abs(targetDrag - drag);
 
        if (dDrag < bestDDrag)
        {
            bestDDrag   = dDrag;
            bestSurface = surface;
        }
    }
 
    return bestSurface;
}
 
float AirBrakesPI::getExtension(float surface)
{
    // clang-format off
    return
        config.EXT_POL_1 * powf(surface, 4) +
        config.EXT_POL_2 * powf(surface, 3) +
        config.EXT_POL_3 * powf(surface, 2) +
        config.EXT_POL_4 * surface;
    // clang-format on
}
 
float AirBrakesPI::getCD(TimedTrajectoryPoint currentPosition, float extension)
{
    const float mach1 = currentPosition.getMac();
    const float mach2 = powf(mach1, 2);
    const float mach3 = powf(mach1, 3);
    const float mach4 = powf(mach1, 4);
    const float mach5 = powf(mach1, 5);
    const float mach6 = powf(mach1, 6);
 
    const float extension2 = powf(extension, 2);
 
    // clang-format off
    return
        config.N000 +
        config.N100 * mach1 +
        config.N200 * mach2 +
        config.N300 * mach3 +
        config.N400 * mach4 +
        config.N500 * mach5 +
        config.N600 * mach6 +
        config.N010 * extension +
        config.N020 * extension2 +
        config.N110 * extension  * mach1 +
        config.N120 * extension2 * mach1 +
        config.N210 * extension  * mach2 +
        config.N220 * extension2 * mach2 +
        config.N310 * extension  * mach3 +
        config.N320 * extension2 * mach3 +
        config.N410 * extension  * mach4 +
        config.N420 * extension2 * mach4 +
        config.N510 * extension  * mach5 +
        config.N520 * extension2 * mach5 +
        config.N001 * currentPosition.z;
    // clang-format on
}
 
float AirBrakesPI::getDrag(TimedTrajectoryPoint currentPosition, float cd,
                           float rho)
{
    return 0.5 * rho * config.S0 * cd * currentPosition.vz *
           currentPosition.vMod;
}
 
void AirBrakesPI::chooseTrajectory(TrajectoryPoint currentPosition)
{
    float minDistance   = numeric_limits<float>::infinity();
    uint8_t trjIndexMin = trajectorySet.length() / 2;
 
    for (uint8_t trjIndex = 0; trjIndex < trajectorySet.length(); trjIndex++)
    {
        Trajectory& trajectory = trajectorySet.trajectories[trjIndex];
 
        for (uint32_t ptIndex = 0; ptIndex < trajectory.size(); ptIndex++)
        {
            TrajectoryPoint point = trajectory.points[ptIndex];
            float distance =
                TrajectoryPoint::distanceSquared(point, currentPosition);
 
            if (distance < minDistance)
            {
                minDistance            = distance;
                trjIndexMin            = trjIndex;
                lastSelectedPointIndex = ptIndex;
                chosenTrajectory       = &trajectory;
            }
        }
    }
 
    chosenTrajectory = &(trajectorySet.trajectories[trjIndexMin]);
}
 
TrajectoryPoint AirBrakesPI::getSetpoint(TrajectoryPoint currentPosition)
{
    if (chosenTrajectory == nullptr)
        return {};
 
    float minDistance = numeric_limits<float>::infinity();
 
    uint32_t end = chosenTrajectory->size();
    for (uint32_t ptIndex = lastSelectedPointIndex; ptIndex < end; ptIndex++)
    {
        float distanceFromCurrentInput =
            abs(chosenTrajectory->points[ptIndex].z - currentPosition.z);
 
        if (distanceFromCurrentInput < minDistance)
        {
            minDistance            = distanceFromCurrentInput;
            lastSelectedPointIndex = ptIndex;
        }
    }
 
    return chosenTrajectory->points[lastSelectedPointIndex];
}
 
float AirBrakesPI::piStep(TimedTrajectoryPoint currentPosition,
                          TrajectoryPoint setPoint, float rho)
{
    const float cdMin   = getCD(currentPosition, 0);
    const float dragMin = getDrag(currentPosition, cdMin, rho);
 
    const float cdMax   = getCD(currentPosition, config.EXTENSION);
    const float dragMax = getDrag(currentPosition, cdMax, rho);
 
    // Get target surface percentage
    const float cdRef   = getCD(currentPosition, chosenTrajectory->extension);
    const float dragRef = getDrag(currentPosition, cdRef, rho);
 
    // PI update
    const float error = currentPosition.vz - setPoint.vz;
    const float dragPi =
        pi.antiWindUp(pi.update(error) + dragRef, dragMin, dragMax);
 
    return dragPi;
}
 
}  // namespace Boardcore