编写一段ros中驱动直流电机的节点代码

下面是一个简单的ROS节点代码，用于驱动直流电机：

#include <ros/ros.h>
#include <std_msgs/Float64.h>
#include <geometry_msgs/Twist.h>

ros::Publisher left_wheel_pub;
ros::Publisher right_wheel_pub;

void cmd_vel_callback(const geometry_msgs::Twist::ConstPtr& msg)
{
    double linear_vel = msg->linear.x;
    double angular_vel = msg->angular.z;
    
    double left_wheel_vel = linear_vel - angular_vel;
    double right_wheel_vel = linear_vel + angular_vel;
    
    std_msgs::Float64 left_wheel_vel_msg;
    std_msgs::Float64 right_wheel_vel_msg;
    left_wheel_vel_msg.data = left_wheel_vel;
    right_wheel_vel_msg.data = right_wheel_vel;
    
    left_wheel_pub.publish(left_wheel_vel_msg);
    right_wheel_pub.publish(right_wheel_vel_msg);
}

int main(int argc, char** argv)
{
    ros::init(argc, argv, "motor_driver");
    
    ros::NodeHandle nh;
    left_wheel_pub = nh.advertise<std_msgs::Float64>("left_wheel/cmd_vel", 10);
    right_wheel_pub = nh.advertise<std_msgs::Float64>("right_wheel/cmd_vel", 10);
    ros::Subscriber cmd_vel_sub = nh.subscribe("cmd_vel", 10, cmd_vel_callback);
    
    ros::spin();
    
    return 0;
}

该节点监听 `cmd_vel` 话题，接收控制指令并计算左右轮的速度，然后分别发布到 `left_wheel/cmd_vel` 和 `right_wheel/cmd_vel` 话题上。在这里，我们假设左右轮分别由两个不同的电机驱动。这里使用 `std_msgs/Float64` 消息类型来表示轮子的速度。