Joystick Control

Attention

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View Package on GitHub

Overview

This package can be used to control the movements of any X-Series robotic arm using a SONY PS3/PS4 controller or Microsoft Xbox360 controller (untested) via Bluetooth. In this demo, the ‘arm’ joints are set to work in ‘position’ control mode while the gripper operates in ‘PWM’ mode. Refer to the joystick button map below to see how to operate the robot. Specifically, some of the joystick controls manipulate individual joints while others are used to perform ‘inverse kinematics’ on all the joints to get the end-effector of the robot (defined at ‘ee_gripper_link’) to move as if it’s in Cartesian space. This is done using the modern_robotics code library offered by Northwestern University.

Structure

../_images/xsarm_joy_flowchart.png

As shown above, the interbotix_xsarm_joy package builds on top of the interbotix_xsarm_control package. To get pointers about the nodes in that package, please look at its README. The other nodes are described below:

  • joy - a ROS driver for a generic Linux joystick; it reads data from a joystick over Bluetooth and publishes sensor_msgs/Joy messages to the commands/joy_raw topic
  • xsarm_joy - responsible for reading in raw sensor_msgs/Joy messages from the commands/joy_raw topic and converting them into ArmJoy messages; this makes the code more readable and allows users to remap buttons very easily later.
  • xsarm_robot - responsible for reading in ArmJoy messages and sending joint and gripper commands to the xs_sdk node; while the ‘waist’ joint can be directly controlled via the PS3/PS4 joystick, other buttons allow position-ik to be performed using all the arm joints.

Usage

After pairing your Bluetooth joystick controller using the Pairing Your Controller Guide, type the following in a terminal (let’s say to control the WidowX-200 arm):

$ roslaunch interbotix_xsarm_joy xsarm_joy.launch robot_model:=wx200

A red error message might appear in the screen saying Couldn't open joystick force feedback!. This is normal and will not affect the joystick operation. To further customize the launch file at run-time, look at the table below:

Argument Description Default Value
robot_model model type of the Interbotix Arm such as ‘wx200’ or ‘rx150’ “”
robot_name name of the robot (typically equal to robot_model, but could be anything) $(arg robot_model)
base_link_frame name of the ‘root’ link on the arm; typically ‘base_link’, but can be changed if attaching the arm to a mobile base that already has a ‘base_link’ frame base_link’
use_rviz launches RViz true
mode_configs the file path to the ‘mode config’ YAML file refer to xsarm_control.launch
threshold value from 0 to 1 defining joystick sensitivity; a larger number means the joystick should be less sensitive 0.75
controller type of controller (‘ps3’, ‘ps4’, or ‘xbox360’) ps4
launch_driver true if the xsarm_control.launch file should be launched - set to false if you would like to run your own version of this file separately true
use_sim if true, the Dynamixel simulator node is run; use RViz to visualize the robot’s motion; if false, the real Dynamixel driver node is run false

To understand how the joystick buttons map to controlling the robot, look at the diagram and table below. Note that while the Xbox360 has a slightly different naming convention, the button placement is essentially the same:

../_images/ps3.jpg
Button Action
START/OPTIONS move robot arm to its Home pose
SELECT/SHARE move robot arm to its Sleep pose
R2 rotate the ‘waist’ joint clockwise
L2 rotate the ‘waist’ joint counterclockwise
Triangle increase gripper pressure in 0.125 step increments (max is 1)
X decrease gripper pressure in 0.125 step increments (min is 0)
O open gripper
Square close gripper
D-pad Up increase the control loop rate in 1 Hz step increments (max of 40)
D-pad Down decrease the control loop rate in 1 Hz step increments (min of 10)
D-pad Left coarse’ control - sets the control loop rate to a user-preset ‘fast’ rate
D-pad Right fine’ control - sets the control loop rate to a user-preset ‘slow’ rate
Right stick Up/Down increase/decrease pitch of the end-effector
Right stick Left/Right increase/decrease roll of the end-effector
R3 reverses the Right stick Left/Right control
Left stick Up/Down move the end-effector (defined at ‘ee_gripper_link’) vertically in Cartesian space
Left stick Left/Right move the end-effector (defined at ‘ee_gripper_link’) horizontally in Cartesian space
L3 reverses the Left stick Left/Right control
R1 if the arm has 6dof, this moves the end-effector in a negative direction along its own ‘y’ axis
L1 if the arm has 6dof, this moves the end-effector in a positive direction along its own ‘y’ axis
PS if torqued on, holding for 3 seconds will torque off the robot; if torqued off, tapping the button will torque on the robot

Video Tutorials

Using a Joystick to Control X-Series Arms


Joystick X-Series Arm Demo