ROS与Arduino学习（八）电机控制(基于rosserial_arduino)

ROS与Arduino学习（八）电机控制(基于rosserial_arduino)

 

Tutorial Level:小案例节点通信

Next Tutorial：ros_arduino_brige固件

 

Tips 1 Arduino上实现ROS Node，订阅Twist msg

a.首先需要包含ros的头文件

#include <PID_v1.h>
#include <ArduinoHardware.h>
#include <ros.h>
#include <geometry_msgs/Twist.h>
#include <ros/time.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>

b. 在声明部分什么node句柄

ros::NodeHandle nh;

 c.定义收到Twist msg后的处理函数

void motor_cb(const geometry_msgs::Twist& vel)
{
  linear = vel.linear.x * 100; //ROS中的单位是m/s;这里换算成cm的单位，在Diego机器人中使用CM作为单位
  angular = vel.angular.z;
}
ros::Subscriber<geometry_msgs::Twist> sub("/turtle1/cmd_vel", motor_cb);/////这里先暂时订阅Turtle1 package的Twist消息，后面根据自己的需要可以修改

 d .在loog中执行

nh.spinOnce();

 到这里Arduino已经可以作为一个Node的节点接收上位机的Twist msg了

Tips 2 底盘驱动及PID控制

 

a. 引脚定义
底盘马达驱动采用了L298P模块

#define E_left 5 //L298P直流电机驱动板的左轮电机使能端口连接到数字接口5
#define M_left 4 //L298P直流电机驱动板的左轮电机转向端口连接到数字接口4
#define E_right 6 //连接小车右轮电机的使能端口到数字接口6
#define M_right 7 //连接小车右轮电机的转向端口到数字接口7

 电机马达码盘中断，

#define Pin_left 2 //外部中断0,左轮
#define Pin_right 3 //外部中断1,右轮

 b.底盘前进控制

void advance()//前进
{
  digitalWrite(M_left, HIGH);
  analogWrite(E_left, val_left);
  digitalWrite(M_right, HIGH);
  analogWrite(E_right, val_right);
}
void back()//后退
{
  digitalWrite(M_left, LOW);
  analogWrite(E_left, val_left);
  digitalWrite(M_right, LOW);
  analogWrite(E_right, val_right);
}
void Stop()//停止
{
  digitalWrite(E_right, LOW);
  digitalWrite(E_left, LOW);
}

 c.PID控制

采用Ardunio的PID控制包Arduino-PID-Library https://github.com/br3ttb/Arduino-PID-Library/

由于需要分别对两个马达控制所以需要分别设定两个马达的PID控制参数

//////PID
double left_Setpoint, left_Input, left_Output, left_setpoint;
double left_kp = 1, left_ki = 0.005, left_kd = 0.0001; 
PID left_PID(&left_Input, &left_Output, &left_Setpoint, left_kp, left_ki, left_kd, DIRECT);

double right_Setpoint, right_Input, right_Output, right_setpoint;
double right_kp = 0.8, right_ki = 0.005, right_kd = 0.0021; 
PID right_PID(&right_Input, &right_Output, &right_Setpoint, right_kp, right_ki, right_kd, DIRECT);

 

       即使相同型号的电机，其PID的调节参数都可能不一样，需要单独调节，需要反复测试调节，相关调节方法可以到百度

#include <PID_v1.h>
//#include <ArduinoHardware.h>
#include <ros.h>
#include <geometry_msgs/Twist.h>
#include <ros/time.h>
#include <tf/transform_broadcaster.h>
#include <nav_msgs/Odometry.h>
#define Pin_left 2 //外部中断0,左轮
#define Pin_right 3 //外部中断1,右轮

#define max_linear  20 //最大线速度cm/秒
#define max_turn_line 18 //最大转弯线速度
//#define max_angular 1.45
#define max_linear_pwd  255

#define hole_number 2 //码盘孔数
#define diameter 18.535 //轮cm直径
#define diamete_ratio 1.12167 //左轮相对于右轮轮径比系数,往左偏,调小,往右偏调大
#define center_speed 220 //小车电机的PWM功率初始值
#define gear_ratio 75 //转速比
#define car_width 27 //小车宽度
#define car_length 27 //小车长度

#define E_left 5 //L298P直流电机驱动板的左轮电机使能端口连接到数字接口5
#define M_left 4 //L298P直流电机驱动板的左轮电机转向端口连接到数字接口4
#define E_right 6 //连接小车右轮电机的使能端口到数字接口6
#define M_right 7 //连接小车右轮电机的转向端口到数字接口7


int val_right_count_target = 0; //小车右轮码盘每秒计数PID调节目标值,根据这个值PID val_rigth;
int val_right = 0; //小车右轮电机的PWM功率值
int val_left_count_target = 0; //小车左轮码盘每秒计数PID调节目标值,根据这个值PID val_left;
int val_left = 0; //左轮电机PWM功率值。以左轮为基速度,PID调节右轮的速度
int count_left = 0;  //左轮编码器码盘脉冲计数值;用于PID调整
int count_right = 0; //右轮编码器码盘脉冲计数值;用于PID调整
/////////
char run_direction = 'f'; //f:前进;b:后退;s:stop
int linear = 0;//15; //cm/second线速度
int angular = 0;//1; //角速度,ros的angular.z
///转弯半径一定要大于小车宽度的一半,也就是linear / angular一定是大于13.5,也就是最小转弯半径是13.5
/////////
unsigned long left_old_time = 0, right_old_time = 0; // 时间标记
unsigned long time1 = 0, time2 = 0; // 时间标记

////ros
ros::NodeHandle nh;
//geometry_msgs::TransformStamped t;
//tf::TransformBroadcaster broadcaster;
//char base_link[] = "/base_link";
//char odom[] = "/odom";
//nav_msgs::Odometry odom1;
void motor_cb(const geometry_msgs::Twist& vel)
{
  linear = vel.linear.x * 100; //ROS中的单位是m/s;这里换算成cm的单位
  angular = vel.angular.z;
}
ros::Subscriber<geometry_msgs::Twist> sub("/turtle1/cmd_vel", motor_cb);

//////PID
double left_Setpoint, left_Input, left_Output, left_setpoint;
double left_kp = 1, left_ki = 0.005, left_kd = 0.0001; //kp = 0.040,ki = 0.0005,kd =0.0011;
PID left_PID(&left_Input, &left_Output, &left_Setpoint, left_kp, left_ki, left_kd, DIRECT);

double right_Setpoint, right_Input, right_Output, right_setpoint;
double right_kp = 0.8, right_ki = 0.005, right_kd = 0.0021; //kp = 0.040,ki = 0.0005,kd =0.0011;
PID right_PID(&right_Input, &right_Output, &right_Setpoint, right_kp, right_ki, right_kd, DIRECT);

void setup() {
  // put your setup code here, to run once:
  Serial.begin(9600);    // 启动串口通信，波特率为9600b/s
  // reserve 200 bytes for the inputString

  pinMode(M_left, OUTPUT);   //L298P直流电机驱动板的控制端口设置为输出模式
  pinMode(E_left, OUTPUT);
  pinMode(M_right, OUTPUT);
  pinMode(E_right, OUTPUT);

  //定义外部中断0和1的中断子程序Code(),中断触发为下跳沿触发
  //当编码器码盘的OUT脉冲信号发生下跳沿中断时，
  //将自动调用执行中断子程序Code()。
  left_old_time = millis();
  right_old_time = millis();
  attachInterrupt(0, Code1, FALLING);//小车左车轮电机的编码器脉冲中断函数
  attachInterrupt(1, Code2, FALLING);//小车右车轮电机的编码器脉冲中断函数

  nh.initNode();
  nh.subscribe(sub);
  //broadcaster.init(nh);
  left_PID.SetOutputLimits(-254, 254);
  left_PID.SetSampleTime(500);
  left_PID.SetMode(AUTOMATIC);
  left_PID.SetTunings(left_kp, left_ki, left_kd);

  right_PID.SetOutputLimits(-254, 254);
  right_PID.SetSampleTime(500);
  right_PID.SetMode(AUTOMATIC);
  right_PID.SetTunings(right_kp, right_ki, right_kd);

}
//子程序程序段
void advance()//前进
{
  digitalWrite(M_left, HIGH);
  analogWrite(E_left, val_left);
  digitalWrite(M_right, HIGH);
  analogWrite(E_right, val_right);
}
void back()//后退
{
  digitalWrite(M_left, LOW);
  analogWrite(E_left, val_left);
  digitalWrite(M_right, LOW);
  analogWrite(E_right, val_right);
}
void Stop()//停止
{
  digitalWrite(E_right, LOW);
  digitalWrite(E_left, LOW);
}
void loop() {

  nh.spinOnce();

  // put your main code here, to run repeatedly:

  if (angular == 0) { //直行
    if (linear > 0) { //前进
      Serial.println("Go Forward!\n");
      if (linear > max_linear)
        linear = max_linear;

      float linear_left = linear; //左内圈线速度
      float linear_right = linear; //右外圈线速度


      val_right_count_target = linear_right * gear_ratio / (diameter / hole_number); //左内圈线速度对应的孔数
      val_left_count_target = linear_left * gear_ratio / (diameter * diamete_ratio / hole_number); //右外圈线速度对应的孔数

      val_right = linear_right * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,左轮
      val_left = linear_left * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,右

      left_Setpoint = val_left_count_target;
      right_Setpoint = val_right_count_target;

      advance();
      run_direction = 'f';
    } else if (linear < 0) { //后退
      Serial.println("Go Backward!\n");
      linear = abs(linear);
      if (linear > max_linear)
        linear = max_linear;
      float linear_left = linear; //左内圈线速度
      float linear_right = linear; //右外圈线速度


      val_right_count_target = linear_right * gear_ratio / (diameter * diamete_ratio / hole_number); //左内圈线速度对应的孔数
      val_left_count_target = linear_left * gear_ratio / (diameter / hole_number); //右外圈线速度对应的孔数

      val_right = linear_right * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,左轮
      val_left = linear_left * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,右轮

      left_Setpoint = val_left_count_target;
      right_Setpoint = val_right_count_target;

      back();
      run_direction = 'b';
    }

  } else if (angular > 0) { //左转
    Serial.println("Turn Left!\n");
    if (linear > max_turn_line) //////限制最大转弯线速度
    {
      angular = angular * max_turn_line / linear;
      linear = max_turn_line;
    } else if (linear == 0) {
      linear = max_turn_line;
    }

    float radius = linear / angular; //计算半径

    if (radius < car_width / 2) ///////如果计算的转弯半径小于最小半径,则设置为最小转弯半径
      radius = car_width / 2;

    float radius_left = radius - car_width / 2; //左内圈半径
    float radius_right = radius + car_width / 2; //右外圈半径

    float linear_left = radius_left * angular; //左内圈线速度
    float linear_right = radius_right * angular; //右外圈线速度

    if (linear == max_turn_line) {
      linear_left = 255 * (linear_left / linear_right);
      linear_right = 255;
    }


    val_right_count_target = linear_right * gear_ratio / (diameter / hole_number); //左内圈线速度对应的孔数
    val_left_count_target = linear_left * gear_ratio / (diameter * diamete_ratio / hole_number); //右外圈线速度对应的孔数

    val_right = linear_right * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,左轮
    val_left = linear_left * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,右轮

    left_Setpoint = val_left_count_target;
    right_Setpoint = val_right_count_target;

    run_direction = 'f';
    advance();

  } else if (angular < 0) { //右转
    Serial.println("Turn Right!");
    if (linear > max_turn_line) //////限制最大转弯线速度
    {
      angular = angular * max_turn_line / linear;
      linear = max_turn_line;

    } else if (linear == 0) {
      linear = max_turn_line;
    }


    float radius = linear / angular;
    if (radius < car_width / 2) ///////如果计算的转弯半径小于最小半径,则设置为最小转弯半径
      radius = car_width / 2;

    float radius_left = radius + car_width / 2;
    float radius_right = radius - car_width / 2;

    float linear_left = radius_left * angular;
    float linear_right = radius_right * angular;

    if (linear == max_turn_line) {
      linear_right = 255 * (linear_right / linear_left);
      linear_left = 255;
    }

    val_right_count_target = linear_right * gear_ratio / (diameter / hole_number); //左内圈线速度对应的孔数
    val_left_count_target = linear_left * gear_ratio / (diameter * diamete_ratio / hole_number); //右外圈线速度对应的孔数

    val_right = linear_right * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,左轮
    val_left = linear_left * (max_linear_pwd / max_linear); //根据轮径参数计算出来的线速度对应的PWD值,右轮

    left_Setpoint = val_left_count_target;
    right_Setpoint = val_right_count_target;

    advance();
    run_direction = 'f';
  }
  delay(1000);
  val_left_count_target = 0;
  left_Setpoint = 0;
  val_right_count_target = 0;
  right_Setpoint = 0;
  linear = 0;
  angular = 0;
  Stop();
  run_direction = 's';
}

void PID_left() {
  Serial.println("********************************begin PID left");

  left_Input = count_left * 10;
  left_PID.Compute();

  val_left = val_left + left_Output;
  if (val_left > 255)
    val_left = 255;
  if (val_left < 0)
    val_left = 0;
  if (run_direction == 'f') //根据刚刚调节后的小车电机PWM功率值，及时修正小车前进或者后退状态
    advance();
  if (run_direction == 'b')
    back();
  Serial.println("********************************end PID Left");
}
void PID_right() {
  Serial.println("********************************begin PID Right");

  right_Input = count_right * 10;
  right_PID.Compute();
  val_right = val_right + right_Output;
  if (val_right > 255)
    val_right = 255;
  if (val_right < 0)
    val_right = 0;
  if (run_direction == 'f') //根据刚刚调节后的小车电机PWM功率值，及时修正小车前进或者后退状态
    advance();
  if (run_direction == 'b')
    back();
  Serial.println("********************************end PID Right");
}

 

        实践证明ROS_lib是非常占用arduino资源的，如果要订阅Twist，同时发布TF，Odometry消息则至少需要3k的SRAM, Arduino UNO只能作为接收Twist消息，来控制底盘，如果用rosserial_arduino做到完整的Base Controller就只能上Arduino Mega2560了，这无疑会增加不少成本，所以笔者认为又更好的选择，那就是使用ros_arduino_bridge作为Base Controller，把逻辑的运算放在上位机上运行，Arduino单纯的作为硬件的控制器，在下一篇，将为大家讲解如何用ros_arduino_bridge作为base controller。