ROS机器人要动起来首先需要对底盘的驱动，在ROS的控制模型中，一般会把对底盘的驱动，及马达的PID调节放在一起称之为base controller，ROS社区已经有针对Arduino封装好的Package—rosserial_arduino，wiki地址为：http://wiki.ros.org/rosserial_arduino/Tutorials，接下来我们一步一步来实现一个Arduino Base conroller
1.rosserial_arduino的安装
安装必须在linux下进行，安装好后可以把Library 拷贝到windows，Mac下的arduino libarary下使用。也可以直接到网盘下载https://pan.baidu.com/s/1eS9MiVg
a.下载
进入你的workspace目录下的src目录，catkin_ws是workspace
cd ~/catkin_ws/src
git clone https://github.com/ros-drivers/rosserial.git- 1
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b.编译，在workspace目录编译
cd <catkin_ws>
catkin_make- 1
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c.在Arduino的/libraries目录下生产Ros包
一般情况Arduino的libraries目录是/home/username/sketchbook/libraries ,其中username代表的是登录linux的用户名
cd /home/username/sketchbook/libraries
rosrun rosserial_arduino make_libraries.py- 1
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如果提示找不到rosserial_arduino make_libraries.py，则需要执行如下代码：
rosserial_arduino make_libraries.py- 1
这时候libraries目录下就会有一个ros_lib的目录，重启Arduino IDE既可以看到Ros_lib包了，可以copy出来在其他电脑上使用
2.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>- 1
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b. 在声明部分什么node句柄
ros::NodeHandle nh;- 1
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- 1
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d .在loog中执行
nh.spinOnce();- 1
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
3.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- 1
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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- 1
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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);
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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);- 1
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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
PID处理函数
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");
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在本中PID调节在两个中断处理函数中调用
// 左侧车轮电机的编码器码盘计数中断子程序
void Code1()
{
//为了不计入噪音干扰脉冲，
//当2次中断之间的时间大于2ms时，计一次有效计数
//Serial.println("Code1");
if ((millis() - time1) > 2) {
//当编码器码盘的OUT脉冲信号下跳沿每中断一次，
count_left++; // 编码器码盘计数加一
if ((millis() - left_old_time) > 100) { ////////100ms进行一次PID调节
PID_left();
left_old_time = millis();
count_left = 0;//把脉冲计数值清零，以便计算下一秒的脉冲计数
}
time1 == millis();
}
}
// 右侧车轮电机的编码器码盘计数中断子程序
void Code2()
{
//Serial.println("Code2");
if ((millis() - time2) > 2) {
//当编码器码盘的OUT脉冲信号下跳沿每中断一次，
count_right++; // 编码器码盘计数加一
if ((millis() - right_old_time) > 100) { ////////100ms进行一次PID调节
PID_right();
right_old_time = millis();
count_right = 0; //把脉冲计数值清零，以便计算下一秒的脉冲计数
}
time2 == millis();
}
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之所以在中断处理函数中调用，ROS Twist的发布时按照一定的频率不断的发送给下位机的，在主loop中不断的接收Twist消息并设定行驶的线速度，和角速度，而PID调节必须比ROS发布短的周期里面去调节速度，如果不能这样PID调节其实就没什么意义了。
3.完整代码
#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() {
// Serial.println("*************************************loop");
// t.header.frame_id = odom;
// t.child_frame_id = base_link;
// t.transform.translation.x = 1.0;
// t.transform.rotation.x = 0.0;
// t.transform.rotation.y = 0.0;
// t.transform.rotation.z = 0.0;
// t.transform.rotation.w = 1.0;
// t.header.stamp = nh.now();
// broadcaster.sendTransform(t);
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;