Integrating NexDroid with ROS

Video

We have produced a video tutorial on connecting the NexDroid system to ROS.

1. Initializing the ROS Environment

Installing the ROS System

This section covers the complete installation steps and how to resolve any errors that may occur.

1. Configure `sources.list`

Configure the computer to install software from packages.ros.org.

sudo sh -c 'echo "deb http://packages.ros.org/ros/ubuntu $(lsb_release -sc) main" > /etc/apt/sources.list.d/ros-latest.list'

If the download is too slow, configure the Tsinghua mirror:

sudo sh -c '. /etc/lsb-release && echo "deb http://mirrors.tuna.tsinghua.edu.cn/ros/ubuntu/ `lsb_release -cs` main" > /etc/apt/sources.list.d/ros-latest.list'

Note: if the download fails, try configuring Alibaba Cloud, Tsinghua, or other mirrors for Ubuntu. An Alibaba Cloud mirror configuration is provided below.

Back up the source list

The default sources configured for Ubuntu are not hosted on servers in China, so downloading and updating software is slow. First, back up the source list file sources.list
```
sudo cp /etc/apt/sources.list /etc/apt/sources.list_backup
```

Open the sources.list file to modify it

sudo gedit /etc/apt/sources.list

Edit the /etc/apt/sources.list file and add the Alibaba Cloud mirror at the top:

deb http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-security main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-updates main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-proposed main restricted universe multiverse
deb-src http://mirrors.aliyun.com/ubuntu/ bionic-backports main restricted universe multiverse

Refresh the package list

sudo apt-get update
sudo apt-get upgrade
sudo apt-get install build-essential

2. Set Up the GPG Key

sudo apt-key adv --keyserver 'hkp://keyserver.ubuntu.com:80' --recv-key C1CF6E31E6BADE8868B172B4F42ED6FBAB17C654

3. Install

sudo apt update
sudo apt install ros-melodic-desktop-full

4. Initialize `rosdep`

If initialization fails, follow the fixes in step 6; after initialization completes, proceed to configure the environment variables.

sudo rosdep init
rosdep update

5. Set Environment Variables

echo "source /opt/ros/melodic/setup.bash" >> ~/.bashrc
source ~/.bashrc

6. Fixing `rosdep` Errors

Due to server issues, you may encounter the following problems, which require modifying the configuration files:

sudo rosdep init
ERROR: cannot download default sources list from:
https://raw.githubusercontent.com/ros/rosdistro/master/rosdep/sources.list.d/20-default.list
Website may be down.

rosdep update
reading in sources list data from /etc/ros/rosdep/sources.list.d
ERROR: error loading sources list:
('The read operation timed out')

Open the file containing the resource-download function:

sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/sources_list.py

Add

url="https://ghproxy.com/"+url

Modify the DEFAULT_INDEX_URL in the /usr/lib/python2.7/dist-packages/rosdistro/__init__.py file

sudo gedit /usr/lib/python2.7/dist-packages/rosdistro/__init__.py

DEFAULT_INDEX_URL = 'https://ghproxy.com/https://raw.githubusercontent.com/ros/rosdistro/master/index-v4.yaml'

Modify the addresses in the other four files by prepending https://ghproxy.com/ to https://raw.githubusercontent.com/

$ sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/gbpdistro_support.py
//modify the address on line 36
$ sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/sources_list.py  //go to line 72
$ sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/rep3.py
//modify line 39
$ sudo gedit /usr/lib/python2.7/dist-packages/rosdistro/manifest_provider/github.py
//modify lines 68 and 119

Fix the "Hit" error on the fifth address

sudo gedit /usr/lib/python2.7/dist-packages/rosdep2/gbpdistro_support.py
//Add the following code on line 204 (i.e., the first line of that function block)
gbpdistro_url = "https://ghproxy.com/" + gbpdistro_url
//Note: the double quotes around the proxy address in the original URL are Chinese quotes; copy-pasting them directly will cause a character-recognition error

If the "Hit" error on the fifth address still persists, modify

sudo gedit /etc/resolv.conf

Comment out the existing nameserver line and add the following two lines:

nameserver 8.8.8.8 #Google DNS server
nameserver 8.8.4.4 #Google DNS server

Save and exit, then run

sudo  apt-get update

Then run

sudo rosdep init
ERROR: default sources list file already exists:
/etc/ros/rosdep/sources.list.d/20-default.list
Please delete if you wish to re-initialize

Solution:

Run the following command to delete the existing initialization file:

sudo rm /etc/ros/rosdep/sources.list.d/20-default.list

Then run again

sudo rosdep init

Installing ROS Packages

sudo apt-get install ros-melodic-moveit
sudo apt-get install ros-melodic-joint-state-publisher
sudo apt-get install ros-melodic-robot-state-publisher
sudo apt install ros-melodic-gazebo-ros-pkgs
sudo apt-get install ros-melodic-gazebo-ros-control
sudo apt-get install  ros-melodic-joint-trajectory-controller

Creating a ROS Workspace

mkdir -p ~/inexbot/src
cd ~/inexbot/src
catkin_init_workspace
cd ../
catkin_make

Modify the ~/.bashrc file

gedit ~/.bashrc

Add the following at the end of the file:

source ~/inexbot/devel/setup.bash

Copy all iNexBot packages into the inexbot/src directory.

2. Configuring MoveIt and the Robot

Before connecting, align the rotation directions, joint angle limits, and maximum joint velocity and acceleration of each axis between ROS and the robot so that they match.

The robot can be configured on the settings screen of the teach pendant.

In ROS, modify the parameters under the axis and limit tags for each joint in the xacro file so that the model's rotation directions and limits match the robot's. Modify max_velocity and max_acceleration in qj_config/config/joint_limits to change the maximum joint velocity and acceleration of the ROS model.

If the rotation directions, joint angle limits, or maximum joint velocity and acceleration are inconsistent, the teach pendant will report angle limit exceeded and servo alarm errors during operation.

......
<joint
name="robot_joint2"		<!--joint name-->
type="revolute">
<origin
  xyz="0 0.18 -0.0525"
  rpy="0 0 0" />
<parent
  link="robot_Link1" />
<child
  link="robot_Link2" />
<axis
  xyz="1 0 0" />    <!--1 for positive direction, -1 for negative-->
<limit
  lower="-3.14"
  upper="3.14"
  effort="100"
  velocity="1" />  <!--lower is the lower joint angle limit, upper is the upper limit; ROS uses radians while the teach pendant uses degrees-->
<dynamics damping="0" friction="1"/>
  </joint>
......

joint_limits:
   robot_joint1:
has_velocity_limits: true
max_velocity: 1
has_acceleration_limits: ture
max_acceleration: 1
<!--max_velocity is the maximum joint velocity, max_acceleration is the maximum joint acceleration, in radians-->
......

3. ROS–Controller Communication

Using a six-axis robot as an example, this section describes how ROS connects to the NRC robot controller.

1. Start the Controller

2. Start the Rviz and Gazebo Co-Simulation Environment

roslaunch inexbot_qj robot_bringup.launch

3. Add the Robot Model

Click Add in the bottom-right corner of the Displays panel, then select Robot Model to add the robot model.

4. Start the ROS Node and Connect to the Controller

rosrun inexbot_service rostopic_joint5

4. Controlling the Robot with MoveIt

1. Goal State Control

Click Plan to generate a planned trajectory; the computation time is displayed at the bottom as Time.

Click Execute to run the trajectory, or click Plan & Execute to plan and run immediately.

2. Drag the Planner Control

Drag the green ball at the front of the planner. When the cursor is placed on the ball, a 3D coordinate frame appears below it. Drag the ball to the target point, click Plan to generate a planned trajectory, then click Execute to run it; you can also click Plan & Execute to plan and run immediately.

5. Controlling the Robot with C++ Programming

1. Create a ROS Package to Store the Program Files

cd ~/inexbot/src
catkin_create_pkg inexbot_code std_msgs rospy roscpp
cd ../
catkin_make

2. Joint-Space Planning

Create `moveit_joint_demo.c`

Place the file under ~/inexbot/src/inexbot_code/src.

//moveit_joint_demo.c
#include <ros/ros.h>
#include <moveit/move_group_interface/move_group_interface.h>

int main(int argc, char **argv)
{
//ROS initialization
ros::init(argc, argv, "moveit_joint_demo");
ros::AsyncSpinner spinner(1);
spinner.start();

//manipulator is the planning group configured in MoveIt
moveit::planning_interface::MoveGroupInterface arm("manipulator");

//allowed error tolerance
arm.setGoalJointTolerance(0.001);
//maximum acceleration
arm.setMaxAccelerationScalingFactor(0.2);
//maximum velocity
arm.setMaxVelocityScalingFactor(0.2);

// Set the goal state to first return the arm to its home position
//home is the preset position in MoveIt
arm.setNamedTarget("home");
//run
arm.move();
sleep(1);
//Set the angles of the six joints in joint space
double targetPose[6] = {0.391410, -0.676384, -0.376217, 0.0, 1.052834, 0.454125};
std::vector<double> joint_group_positions(6);
joint_group_positions[0] = targetPose[0];
joint_group_positions[1] = targetPose[1];
joint_group_positions[2] = targetPose[2];
joint_group_positions[3] = targetPose[3];
joint_group_positions[4] = targetPose[4];
joint_group_positions[5] = targetPose[5];

arm.setJointValueTarget(joint_group_positions);
arm.move();
sleep(1);

// Return the arm to its home position
arm.setNamedTarget("home");
arm.move();
sleep(1);

ros::shutdown();

return 0;
}

Modify the `CMakeLists.txt` File

Add the following above the install section:

add_executable(moveit_joint_demo src/moveit_joint_demo.cpp)
target_link_libraries(moveit_joint_demo ${catkin_LIBRARIES})
#############
## Install ##
#############

Compile the Code

cd ~/inexbot
catkin_make

Run

rosrun inexbot_code moveit_joint_demo