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Here is a solution by using /joint_states topic

the Arduino subscribes to this topic and controls 5 servo motors in this example

https://github.com/smart-methods/arduino_robot_arm_gripper/blob/main/arduino_code/arduino_code.ino

this a python code publishes to /joint_states topic

#!/usr/bin/env python

import rospy
from sensor_msgs.msg import JointState
from std_msgs.msg import Header


def talker():
    pub = rospy.Publisher('joint_states', JointState, queue_size=10)
    rospy.init_node('joint_state_publisher')
    rate = rospy.Rate(10) # 10hz
    joints_str = JointState()
    joints_str.header = Header()
    joints_str.header.stamp = rospy.Time.now()
    joints_str.name = ['base_joint', 'shoulder', 'elbow', 'wrist', 'gripper']
    joints_str.position = [0.5, 0.5, 0.5, 0.5, 0.0]
    while not rospy.is_shutdown():
      joints_str.header.stamp = rospy.Time.now()
      pub.publish(joints_str)
      rospy.loginfo("position updated")
      rate.sleep()

if __name__ == '__main__':
    try:
        talker()
    except rospy.ROSInterruptException:
        pass

Here is a solution by using /joint_states topic

the Arduino subscribes to this topic and controls 5 servo motors in this example

https://github.com/smart-methods/arduino_robot_arm_gripper/blob/main/arduino_code/arduino_code.ino

this a python code publishes to /joint_states topic

#!/usr/bin/env python

import rospy
from sensor_msgs.msg import JointState
from std_msgs.msg import Header


def talker():
    pub = rospy.Publisher('joint_states', JointState, queue_size=10)
    rospy.init_node('joint_state_publisher')
    rate = rospy.Rate(10) # 10hz
    joints_str = JointState()
    joints_str.header = Header()
    joints_str.header.stamp = rospy.Time.now()
    joints_str.name = ['base_joint', 'shoulder', 'elbow', 'wrist', 'gripper']
    joints_str.position = [0.5, 0.5, 0.5, 0.5, 0.0]
    while not rospy.is_shutdown():
      joints_str.header.stamp = rospy.Time.now()
      pub.publish(joints_str)
      rospy.loginfo("position updated")
      rate.sleep()

if __name__ == '__main__':
    try:
        talker()
    except rospy.ROSInterruptException:
        pass