Hi, I'm running Ubuntu 18.04, melodic.
I'm very new to ROS in general (1 week new), so hopefully you guys can be a bit more patient. So anyway, I wrote a Python publisher for my (differential drive) car. It supposed to send the joint state of my two wheels to RVIZ, and in RVIZ, I supposed to see my car moving with the set speed coming from python side.
It didn't happen. I think maybe I'm missing something, or misunderstood something? If you guys can point that out, it would be great!
Here's my Python side:
Hi, I'm very new to ROS in general (1 week new), so hopefully you guys can be a bit more patient. So anyway, I wrote a Python publisher for my (differential drive) car. It supposed to send the joint state of my two wheels to RVIZ, and in RVIZ, I supposed to see my car moving with the set speed coming from python side.
It didn't happen. I think maybe I'm missing something, or misunderstood something? If you guys can point that out, it would be great!
Here's my Python side:
#!/usr/bin/env python
import rospy
from std_msgs.msg import Header
from sensor_msgs.msg import JointState
def talker():
pub = rospy.Publisher('joint_states', JointState, queue_size=10)
rospy.init_node('joint_state_publisher', anonymous = True)
rate = rospy.Rate(10) # 10hz
while not rospy.is_shutdown():
jointState_msg = JointState()
jointState_msg.header = Header()
jointState_msg.header.stamp = rospy.Time.now()
jointState_msg.name = ['left_wheel_holder_to_left_wheel', 'right_wheel_holder_to_right_wheel']
jointState_msg.position = []
jointState_msg.velocity = [1, 1]
jointState_msg.effort = []
pub.publish(jointState_msg)
rate.sleep()
if __name__ == '__main__':
try:
talker()
except rospy.ROSInterruptException:
pass
Here's my launch file:
<launch>
<param name="robot_description" textfile="$(find rover_project)/rover_description/urdf/rover.urdf"/>
<node name="robot_state_publisher" pkg="robot_state_publisher" type="state_publisher" />
<node name="rviz" pkg="rviz" type="rviz" args="-d $(find rover_project)/rover_description/launch/rviz_config.rviz" />
<node pkg="robot_state_publisher" type="robot_state_publisher" name="rob_st_pub">
<param name="use_gui" value="True"/>
</node>
<node name="joint_state_publisher" pkg="joint_state_publisher" type="joint_state_publisher">
<param name="use_gui" value="True"/>
</node>
</launch>
And most importantly, and this is where I think went wrong, my urdf file:
<?xml version="1.0"?>
<robot xmlns:xacro="http://www.ros.org/wiki/xacro" name="Rover Platform">
<material name="blue">
<color rgba="0 0 0.8 1"/>
</material>
<material name="grey">
<color rgba="0.2 0.2 0 1"/>
</material>
<xacro:macro name="default_origin">
<origin rpy="0 0 0" xyz="0 0 0"/>
</xacro:macro>
<link name="base_link">
<visual>
<geometry>
<box size="1.0 1.0 0.2"/>
</geometry>
<xacro:default_origin />
<material name="blue"/>
</visual>
<collision>
<geometry>
<box size="1.0 1.0 0.2"/>
</geometry>
</collision>
<inertial>
<mass value="5"/>
<inertia ixx="0.83333" ixy="0.0" ixz="0.0" iyy="0.433333" iyz="0.0" izz="0.433333"/>
</inertial>
</link>
<link name="right_wheel_holder_link">
<visual>
<xacro:default_origin />
<geometry>
<box size="0.3 0.2 0.2"/>
</geometry>
<material name="blue"/>
</visual>
<collision>
<geometry>
<box size="0.3 0.2 0.2"/>
</geometry>
</collision>
<inertial>
<mass value="1"/>
<inertia ixx="0.011" ixy="0.0" ixz="0.0" iyy="0.0067" iyz="0.0" izz="0.011"/>
</inertial>
</link>
<link name="left_wheel_holder_link">
<visual>
<xacro:default_origin />
<geometry>
<box size="0.3 0.2 0.2"/>
</geometry>
<material name="blue"/>
</visual>
<collision>
<geometry>
<box size="0.3 0.2 0.2"/>
</geometry>
</collision>
<inertial>
<mass value="1"/>
<inertia ixx="0.011" ixy="0.0" ixz="0.0" iyy="0.0067" iyz="0.0" izz="0.011"/>
</inertial>
</link>
<link name="right_wheel_link">
<visual>
<origin rpy="0 0 0" xyz="0 0 0"/>
<geometry>
<cylinder length="0.05" radius="0.25"/>
</geometry>
<material name="grey"/>
</visual>
<collision>
<geometry>
<cylinder length="0.05" radius="0.25"/>
</geometry>
</collision>
<inertial>
<mass value="1"/>
<inertia ixx="0.00021" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.00021"/>
</inertial>
</link>
<link name="left_wheel_link">
<visual>
<origin rpy="0 0 0" xyz="0 0 0"/>
<geometry>
<cylinder length="0.05" radius="0.25"/>
</geometry>
<material name="grey"/>
</visual>
<collision>
<geometry>
<cylinder length="0.05" radius="0.25"/>
</geometry>
</collision>
<inertial>
<mass value="1"/>
<inertia ixx="0.00021" ixy="0.0" ixz="0.0" iyy="0.0" iyz="0.0" izz="0.00021"/>
</inertial>
</link>
<joint name="base_to_right_wheel_holder" type="fixed">
<parent link="base_link"/>
<child link="right_wheel_holder_link"/>
<origin rpy="0 0 0" xyz="0.4 0.2 -0.2"/>
</joint>
<joint name="base_to_left_wheel_holder" type="fixed">
<parent link="base_link"/>
<child link="left_wheel_holder_link"/>
<origin rpy="0 0 0" xyz="-0.4 0.2 -0.2"/>
</joint>
<joint name="left_wheel_holder_to_left_wheel" type="continuous">
<axis xyz="0 0 1"/>
<parent link="left_wheel_holder_link"/>
<child link="left_wheel_link"/>
<origin rpy="0 -1.57075 0" xyz="-0.15 0 0"/>
</joint>
<joint name="right_wheel_holder_to_right_wheel" type="continuous">
<axis xyz="0 0 1"/>
<parent link="right_wheel_holder_link"/>
<child link="right_wheel_link"/>
<origin rpy="0 1.57075 0" xyz="0.15 0 0"/>
</joint>
<transmission>
<type>transmission_interface/SimpleTransmission</type>
<joint name="left_wheel_holder_to_left_wheel">
<hardwareInterface>EffortJointInterface</hardwareInterface>
</joint>
<actuator name="motor_left">
<hardwareInterface>EffortJointInterface</hardwareInterface>
<mechanicalReduction>1</mechanicalReduction>
</actuator>
<joint name="right_wheel_holder_to_left_wheel">
<hardwareInterface>EffortJointInterface</hardwareInterface>
</joint>
<actuator name="motor_right">
<hardwareInterface>EffortJointInterface</hardwareInterface>
<mechanicalReduction>1</mechanicalReduction>
</actuator>
</transmission>
</robot>
I also did not modify my CMakeLists file, I wonder if I have to though...
