Joint Position Example

Summary

The Joint Position Control Examples demonstrate how to use position control to move and sense the arm based on joint angles. Examples include keyboard or joystick based user control of arm angles, along with complementary example programs to record and playback joint positions.

Code Walkthrough

Joint Position Joystick - Code Walkthrough, Joint Position Recorder - Code Walkthrough, Joint Position File Playback - Code Walkthrough

Overview

The joint_position example allows control of Baxter's arm in joint position mode. Either the keyboard or a joystick can be used as a controller. Joint names are labeled below.

Note: For control of Head Joints, see the Head Wobbler Example.

Keyboard Control

Start the example joint_position program using the keyboard to control Baxter:

   $ rosrun baxter_examples joint_position_keyboard.py

Joystick Control

To run the example joint_position program using a joystick game controller to control the joints:

First ensure that joy drivers are installed.

   $ rospack find joy

If it returns an error.

   [rospack] Error: stack/package joy not found

then run:

   $ sudo apt-get install ros-indigo-joystick-drivers

Run the above rospack command again to ensure that the drivers are successfully installed. If it again returns an error <redirect to troubleshooting section that shows to source the bash script>

To run the example:

   $ roslaunch baxter_examples joint_position_joystick.launch joystick:=<joystick_type>

Where <joystick_type> is 'xbox', 'logitech', or 'ps3'. (If using a ps3, make sure you run the node from the ROS ps3joy package in a separate sudo terminal. See instructions here: ps3joy )

Joystick Button Mappings

NOTE: Don't forget to calibrate each gripper before using gripper open/close.

Buttons	Action	Buttons	Action
Function 1 or 2 (e.g. Select/Select)	Help	<Any Keyboard key>	Quit
Left Button (X)	right: gripper calibrate	Right Button (B)	left: gripper calibrate
Top Button (Y)		Bottom Button (A)
Left Trigger [PRESS]	right: gripper close	Right Trigger [PRESS]	left: gripper close
Left Trigger [RELEASE]	right: gripper open	Right Trigger [RELEASE]	left: gripper open
Left Bumper	right: cycle `<current joints> +1`	Right Bumper	left: cycle `<current joints> +1`

Stick Axes	Action
Left Stick Horizontal	right: increase/decrease `<current joint 1>` (s0)
Left Stick Vertical	right: increase/decrease `<current joint 2>` (s1)
Right Stick Horizontal	left: increase/decrease `<current joint 1>` (s0)
Right Stick Vertical	left: increase/decrease `<current joint 2>` (s1)

NOTE: The 'joystick left <-> robot right' mappings are not typos; they assume the user is in front of the robot when using the joystick. Press any keyboard key to quit.

NOTE: The left and right bumper buttons will cycle through the joints that are controlled with the left and right stick (<current joint 1> and <current joint 2>). The order the joints are cycled through is S0-S1-E0-E1-W0-W1-W2.

Alternative Manual Start

Alternatively, you can run the joint_position example and the joy_node (joystick driver) independently in their own shells:

1. Initialize an environment and run the joy_node:

   $ cd ~/ros_ws
   $ ./baxter.sh
   $ rosrun joy joy_node

2. From another shell, repeat the initialization and run the example program:

   = repeat lines 1-2 above =
   $ rosrun baxter_examples joint_position_joystick.py -j xbox

For the joystick examples to work, the joy_node driver must be running at the same time as the example. Using any of the other one-line launch commands to start the joystick examples is really just using a short-cut to start two programs at once.

Recording Joint Positions

To start recording the joint positions at any time use:

   $ rosrun baxter_examples joint_recorder.py -f <filename>

NOTE: You can open and close the grippers while recording by using Baxter's cuff buttons: Oval = Close, Circle = Open

After you have finished recording, stop the joint_position program using <Ctrl-C> or hit one of the function 1 or 2 buttons on the game controller.

Playback Recordings

To playback the recording use:

   $ rosrun baxter_examples joint_position_file_playback.py -f <filename>