Control PhantomX Pincher Arm

In this tutorial, we will show you how to configure and remotely control PhantomX Pincher Robot connected to the Rover.

source: trossenrobotics.com

Prerequisites

Before you begin, make sure you have internet connection on your Rover.

Also, you need to have ROS installed on your computer.

And, of course, assembled Pincher Arm together with ArbotiX-M Robocontroller connected to your Rover.

1. On your computer

1.1 Flash ArbotiX-M Robocontroller board

To program Arbotix board, you can follow the Getting Started Guide from Trossen Robotics.

If everything works, open and upload the following sketch

File -> Sketchbook -> ArbotiX Sketches -> ros

1.2 Install Arbotix ROS drivers

You can install arbotix ROS packages from repository (ros-kinetic-arbotix package), but for the pincher gripper to fully work, you need to build an unrealeased 0.11.0 version which adds support for prismatic joints.

To build it, you can follow these steps:

source /opt/ros/kinetic/setup.bash
mkdir -p ~/ros_ws/src && cd ~/ros_ws/src
git clone https://github.com/corb555/arbotix_ros
cd ~/ros_ws
rosdep update
rosdep install --from-paths src -iry
catkin build

1.3 Set Dynamixel IDs

Connect Arbotix-M board to your computer through FTDI-USB Cable

Source your catkin workspace (either /opt/ros/kinetic or ~/ros_ws/devel depending on how you installed Arbotix ROS drivers) and run:

arbotix_terminal

arbotix_terminal by default, assumes the board is connected on /dev/ttyUSB0 port. If it is attached to another device, you can specify it like this:

arbotix_terminal [PORT]

To check which port the device connects to, you can, for instance, run dmesg -w (Ctrl+C to exit), connect the device and check kernel logs.

If you are using Ubuntu on Windows Subsytem for Linux , you need to open Device Manager and look under Ports for COM port number of the device. COM[N] corresponds to /dev/ttyS[N] path. (e.g. COM4 -> /dev/ttyS4). You might need to run:

sudo chmod 666 /dev/ttyS[N]

A terminal prompt should appear. Type help for list of commands.

Connect the Dynamixel you want to set id to. Then type ls to see id of connected servo and mv [source] [target] to change it. For example, when the servo has id 1 and we want to set it to 2, just type mv 1 2.

On PhantomX pincher arm, servo ids should look like this:

source: trossenrobotics.com

When done, type Ctrl+C to exit the terminal

1.4 Test Arbotix ROS drivers

We will create a package that tests arbotix driver. Let's start by creating an empty package

source /opt/ros/kinetic/setup.bash
mkdir -p ~/ros_ws/src && cd ~/ros_ws/src
catkin create pkg arbotix_test --catkin-deps arbotix_python

Inside your package, create config/test.yaml file with following content (change port if needed):

port: /dev/ttyUSB0
rate: 15
joints: {
servo1: {id: 1},
servo2: {id: 2},
servo3: {id: 3},
servo4: {id: 4},
servo5: {id: 5}
}

You can set more parameters for each joint, like maximum speed, minimum and maximum angle etc. A brief documentation (Unfortunately, a little outdated) can be found here

And launch/test.launch with following:

<launch>
<node name="arbotix" pkg="arbotix_python" type="arbotix_driver" output="screen">
<rosparam file="$(find arbotix_test)/config/test.yaml" command="load" />
</node>
</launch>

Now, build your workspace

cd ~/ros_ws
catkin build

From now on, you need to run source ~/ros_ws/devel/setup.bash on every terminal session you open (or add it to ~/.bashrc)

Run Master node on one terminal

roscore

And on another, run your launch file

roslaunch arbotix_test test.launch

Now, check available topics and services

rostopic list
rosservice list

You should see command topics that let you set position (in radians) for each servo and joint_states topic that informs about position and velocity of each joint. There should also be services that allow enabling, relaxing or setting speed (in radians/sec) for each servo.

Let's try to move servo1 joint.

First, set speed to a safe value (0.2 r/s in this case):

rosservice call /servo1/set_speed 0.2

Move servo to a default neutral value:

rostopic pub /servo1/command std_mgs/Float64 -- 0.0

The maximum angle range for a dynamixel servo is [-150, 150] degrees which is equal to approximately [-2.62, 2.62] in radians

Relax joint:

rosservice call /servo1/relax

You can also use arbotix_gui to control each joint. Just type:

arbotix_gui

A graphical application should appear:

Enable and relax servos by clicking on checkboxes and set position by moving sliders.

Summary

Here's a recording of a terminal session in which we do things mentioned in the tutorial up to this point:

asciicast

1.5 Install turtlebot_arm packages

The turtlebot_arm packages contain very useful utilities for PhantomX Pincher arm such as:

  • configuration for arbotix driver

  • URDF model of the arm

  • Moveit! configuration package

  • IKFast Kinematics solver plugin

  • MoveIt! pick and place demo

Let's build it

source ~/ros_ws/devel/setup.bash
cd ~/ros_ws/src
git clone https://github.com/turtlebot/turtlebot_arm.git -b kinetic-devel
cd ~/ros_ws
rosdep install --from-paths src -iry
catkin build

To use this packages with PhantomX Pincher, you need to have TURTLEBOT_ARM1 environment variable set to pincher . To set it automatically on every terminal session, add export command to .bashrc file:

echo "export TURTLEBOT_ARM1=pincher" >> ~/.bashrc
source ~/.bashrc

Make sure to have roscore running, then type:

roslaunch turtlebot_arm_bringup arm.launch

This should run Arbotix driver, robot_state_publisher and set robot_description parameter.

To view robot arm model with actual position:

  • Open rviz

  • For Fixed Frame select arm_base_link

  • Click Add in Displays panel

  • Select RobotModel and click Ok

To test Motion Planning with MoveIt! :

  • Run turtlebot_arm_moveit launch file:

    roslaunch turtlebot_arm_moveit_config turtlebot_arm_moveit.launch sim:=false
  • Click on Planning tab in Motion Planning display

  • Move interactive marker to intended position

  • Click on Plan to see Motion visualization and then Execute or just click on Plan and Execute

  • Run pick and place demo (in another terminal session)

    rosrun turtlebot_arm_moveit_demos pick_and_place.py

2. On your Rover

2.1 Prepare catkin workspace

Let's prepare a catkin workspace for pincher arm. Start by sourcing the workspace you want to extend. If you don't have an existing development workspace, just do:

source /opt/ros/kinetic/setup.bash

Download necessary packages

mkdir -p ~/ros_ws/src && cd ~/ros_ws/src
git clone https://github.com/corb555/arbotix_ros.git
git clone https://github.com/turtlebot/turtlebot_arm.git

We only need turtlebot_arm_bringup and turtlebot_arm_description packages, so we can remove the rest

cd ~/ros_ws/src/turtlebot_arm
mv turtlebot_arm_bringup turtlebot_arm_description ~/ros_ws/src
cd ~/ros_ws/src
rm -rf turtlebot_arm

Use rosdep to install missing dependencies

cd ~/ros_ws
rosdep update
rosdep install --from-paths src -iry

Now, build the workspace

catkin build -j 2

2.2 Start necessary Nodes

Source your workspace

source ~/ros_ws/devel/setup.bash

For ROS to work on multiple machines, you need to set specific Environment Variables:

export TURTLEBOT_ARM1=pincher
export ROS_IP=10.0.0.1
export ROS_MASTER_URI=http://10.0.0.1:11311

Add these lines to ~/.bashrc to set them automatically

Now, run Master node on one terminal

roscore

And on another, type:

roslaunch turtlebot_arm_bringup arm.launch

2.3 Control the arm from your computer

Source your workspace containing turtlebot_arm packages

source ~/ros_ws/devel/setup.bash

Set required variables

export TURTLEBOT_ARM1=pincher
export ROS_IP=X.X.X.X
export ROS_MASTER_URI=http://10.0.0.1:11311

Replace X.X.X.X with your local IP address. To check your address, you can use ip address command

You can now use the examples we described earlier, e.g.:

arbotix_gui

or MoveIt! demo:

roslaunch turtlebot_arm_moveit_config turtlebot_arm_moveit.launch sim:=false