Joystick Control

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Overview

This package can be used to control the movements of any rover in the Interbotix X-Series LoCoBot Family using a SONY PS3 or PS4 controller via Bluetooth. In this demo, the ‘arm’ (if equipped) and ‘pan/tilt’ servos work in ‘position’ control mode, the gripper operates in ‘PWM’ mode, and the Kobuki base operates in ‘velocity’ control 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/xslocobot_joy_flowchart.png

As shown above, the interbotix_xslocobot_joy package builds on top of the interbotix_xslocobot_control package. To get familiar with the nodes in the interbotix_xslocobot_control 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 SONY PS3 or PS4 controller joystick over Bluetooth and publishes sensor_msgs/Joy messages to the /<robot_name>/commands/joy_raw topic
  • xslocobot_joy - responsible for reading in raw sensor_msgs/Joy messages from the /<robot_name>/commands/joy_raw topic and converting them into LocobotJoy messages; this makes the code more readable and allows users to remap buttons very easily later. The new messages are then published on the /<robot_name>/commands/joy_processed topic.
  • xslocobot_robot - responsible for reading in LocobotJoy messages from the /<robot_name>/commands/joy_processed topic and publishing joint, gripper, and pan/tilt commands to the xs_sdk node; while the ‘waist’ joint is directly controlled via the PS3/PS4 joystick, other buttons allow position-ik to be performed using all the arm joints. It also publishes velocity commands to the Kobuki base.

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 locobot_wx200 robot with no lidar):

$ roslaunch interbotix_xslocobot_joy xslocobot_joy.launch robot_model:=locobot_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 Locobot such as ‘locobot_base’ or ‘locobot_wx250s’ “”
robot_name name of the robot (could be anything but defaults to ‘locobot’) “locobot”
use_rviz launches RViz; if you are SSH’d into the robot, DON’T set this to true false
rviz_frame fixed frame in RViz; this should be changed to map or <robot_name>/odom if mapping or using local odometry respectively $(arg robot_name)/odom
use_base if true, the Kobuki ROS nodes are launched true
use_lidar if true, the RPLidar node is launched false
show_lidar set to true if the lidar is installed on the robot; this will load the lidar related links to the ‘robot_description’ parameter $(arg use_lidar)
use_camera if true, the RealSense D435 camera nodes are launched false
threshold value from 0 to 1 defining joystick sensitivity; a larger number means the joystick should be less sensitive 0.75
controller type of PlayStation controller (‘ps3’ or ‘ps4’) ps4
mode_configs the file path to the ‘mode config’ YAML file refer to xslocobot_joy.launch
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:

../_images/ps3.jpg

Base Control Mode

Button Action
Left stick Up/Down drive the Kobuki base forward/backward between 0.7 to -0.7 m/s
R2 rotate the Kobuki base clockwise between 0 and -3.14 rad/s
L2 rotate the Kobuki base counterclockwise between 0 and 3.14 rad/s
SELECT/SHARE Reset the odometry of the base to an ‘x’, ‘y’, and ‘theta’ of 0 (the base chirps as well)
Right stick Up/Down tilt the RealSense camera Up/Down
Right stick Left/Right pan the RealSense camera Left/Right
START/OPTIONS move the pan/tilt servo to ‘0’ radians

Arm Control Mode

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
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

Both Modes

Button Action
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
PS shift to the other Control Mode