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02---控制移动底座5

2024-09-11 06:42:47   217人阅读

在大多数时间都是依靠ROS节点来发布恰当的Twist消息。举个简单的例子，假设我们想编程使机器人向前移动1m，旋转180度，然后返回开始的位置。我们会尝试用不同的方法来完成这个任务，这些方法很好地表现了ROS不同层次的运动控制。

1、通过定时和定速估计距离和角度

我们第一个尝试是用定时的Twist命令去让机器人花一定时间向前移动一定的距离，旋转180度后，然后以相同的速度进行相同时长的向前移动，不出意外的话它会回到开始的位置。最后我们会让机器人旋转180度回到最初的方向。

这段脚本可以在子目录rbx1_nav/nodes下的timed_out_and_back.py中找到。

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2、在ArbotiX模拟器上进行计时前进并返回运动

为了保证模拟的TurtleBot回到开始的位置，按下“Ctrl-C”让模拟的TurtleBot中正在运行的启动文件停止运行，然后用以下命令让它重新运行：

roslaunch rbx1_bringup fake_turtlebot.launch

如果你愿意的话，可以用对应Pi Robot或者你自己的机器人的文件替换掉fake_turtlebot.launch，这不会使结果有差别。

如果RViz并不是正在运行，那么就让它开始运行：

rosrun rviz rviz -d `rospack find rbx1_nav`/sim.rviz

或者按下Reset按钮删除掉在上一部分留下的Odometry箭头。

最后运行timed_out_and_back.py节点：

rosrun rbx1_nav timed_out_and_back.py

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3、计时前进并返回运动的脚本

以下是计时前进并返回节点的完整脚本。

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#!/usr/bin/env python

import rospy
from geometry_msgs.msg import Twist
from math import pi

class OutAndBack():
    def __init__(self):
        # Give the node a name
        rospy.init_node(‘out_and_back‘, anonymous=False)

        # Set rospy to execute a shutdown function when exiting       
        rospy.on_shutdown(self.shutdown)
        
        # Publisher to control the robot‘s speed
        self.cmd_vel = rospy.Publisher(‘/cmd_vel‘, Twist, queue_size=1)
        
        # How fast will we update the robot‘s movement?
        rate = 50
        
        # Set the equivalent ROS rate variable
        r = rospy.Rate(rate)
        
        # Set the forward linear speed to 0.2 meters per second 
        linear_speed = 0.2
        
        # Set the travel distance to 1.0 meters
        goal_distance = 1.0
        
        # How long should it take us to get there?
        linear_duration = goal_distance / linear_speed
        
        # Set the rotation speed to 1.0 radians per second
        angular_speed = 1.0
        
        # Set the rotation angle to Pi radians (180 degrees)
        goal_angle = pi
        
        # How long should it take to rotate?
        angular_duration = goal_angle / angular_speed
     
        # Loop through the two legs of the trip  
        for i in range(2):
            # Initialize the movement command
            move_cmd = Twist()
            
            # Set the forward speed
            move_cmd.linear.x = linear_speed
            
            # Move forward for a time to go the desired distance
            ticks = int(linear_duration * rate)
            
            for t in range(ticks):
                self.cmd_vel.publish(move_cmd)
                r.sleep()
            
            # Stop the robot before the rotation
            move_cmd = Twist()
            self.cmd_vel.publish(move_cmd)
            rospy.sleep(1)
            
            # Now rotate left roughly 180 degrees  
            
            # Set the angular speed
            move_cmd.angular.z = angular_speed

            # Rotate for a time to go 180 degrees
            ticks = int(goal_angle * rate)
            
            for t in range(ticks):           
                self.cmd_vel.publish(move_cmd)
                r.sleep()
                
            # Stop the robot before the next leg
            move_cmd = Twist()
            self.cmd_vel.publish(move_cmd)
            rospy.sleep(1)    
            
        # Stop the robot
        self.cmd_vel.publish(Twist())
        
    def shutdown(self):
        # Always stop the robot when shutting down the node.
        rospy.loginfo("Stopping the robot...")
        self.cmd_vel.publish(Twist())
        rospy.sleep(1)
 
if __name__ == ‘__main__‘:
    try:
        OutAndBack()
    except:
        rospy.loginfo("Out-and-Back node terminated.")
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02---控制移动底座5


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