ROS2 Python Joystick controller

Remotely control your robot via cmd_vel topic
Input: 3x axis analog joystick (X + Y + Z/Twist)
Output: ROS node (ROS2) that publish topic /cmd_vel with msg.type twist_stamped

• Angular = X-axis = Pull stick Left/Right
• Linear = Y-axis = Pull stick Up/Down
• Twist = Z-axis = Turn/Twist stick (Not used right now)

ROS2 Package/Module Behaviour

1. Once: Read/Set all the parameters
2. Repeatedly: Read analog joystick via ADC
3. Repeatedly: Transform indata to a +/-100% values
4. Repeatedly: Map where the stick are => Depending om location, then adjust behivaiur.
5. Repeatedly: Transform X, Y movment into Linear & Angaular according to twist msg.type
6. Repeatedly: Publish ros-topic

flowchart TD
    Init      --> Read_A/D
    Joystick  --> |0-3.3V|Read_A/D
    Read_A/D --> Joystick
    Read_A/D --> |0-32000|Transform
    Transform --> |-100..+100|Map
    Map       --> |-100..+100|Twistify
    Twistify  --> |m/s + rad/s|Publish
    Publish   --> |Loop|Read_A/D

Prerequisite: Hardware

• Single Board Computer(SBC): Raspberry Pi 3/4
• A/D converter: KY-053 Analog Digital Converter (ADS1115, 16-bit) via default I2C adr.=0x48
• Joystick: 3x analog 10K resistors. X-, Y- and Twist-axis.

🌐Google tips to find/order Joystick from eBay/AliExpress/Wish/Amazon/...
1) "3-axis analog joystick"
2) "XYZ analog joystick"

# Prerequisite: Software * Ubuntu 20.04 (64bit) or newer * Robot Operating System 2, ROS2 (Version Galactic)

...do the ROS2-installation stuff...

Prerequisite: I2C-interface Raspberry Pi 4 / Ubuntu

Prepared by adding additional, i2c communication, Linux-software-packages
Ubuntu Shell

~$ sudo apt install i2c-tools
~$ sudo apt install python3-pip
~$ sudo pip3 install smbus2
~$ sudo pip3 install adafruit-ads1x15
~$ sudo i2cdetect -y 1
        0  1  2  3  4  5  6  7  8  9  a  b  c  d  e  f
   00:          -- -- -- -- -- -- -- -- -- -- -- -- -- 
   10: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
   20: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
   30: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
   40: -- -- -- -- -- -- -- -- 48 -- -- -- -- -- -- -- 
   50: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
   60: -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- 
   70: -- -- -- -- -- -- -- --    
$ sudo chmod a+rw /dev/i2c-1

Dowload and install this ROS2 packages

Create a ROS2 workspace (in my exampel '~/ws_ros2/')
Dowload ROS2 package by using 'git clone'

🤔There is probably better tutorials how to do this...
...but here is how I made it.

Ubuntu Shell

~$ mkdir -p ~/ws_ros2/src
~$ cd ~/ws_ros2/src
~/ws_ros2/src$ git clone https://github.com/Pet-Series/pet_ros2_joystick_pkg.git
~/ws_ros2/src$ cd ..
~/ws_ros2$ colcon build --symlink-install
~/ws_ros2$ source /opt/ros/galactic/setup.bash
~/ws_ros2$ source ./install/setup.bash

ROS2 Launch sequence

Ubuntu Shell

~/ws_ros2$ ros2 run pet_ros2_joystick_pkg pet_joystick_node
  [INFO] [1645471061.181057770] [joystick_node]: joystick_node has started
  [INFO] [1645471061.183638877] [joystick_node]: - A/D: 0x48, X-chn: 3, Y-chn: 1, Twist-chn: 2
  [INFO] [1645471061.186369983] [joystick_node]: - A/D sampling: 10.0Hz, Topic: twist/cmd_vel

ROS2 Topics used by this package

The pet_joystick_node parallel publishes three variants of topics messages.

1. /raw/joystick using msg.type Joy from sensor_msgs.msg
2. /twist/cmd_vel using msg.type Twist from geometry_msgs.msg
3. /twist_stamped/cmd_vel using msg.type TwistStamped from geometry_msgs.msg

Ubuntu Shell

~/ws_ros2$ ros2 topic list
  /raw/joystick
  /twist/cmd_vel
  /twist_stamped/cmd_vel

ROS2 Parameters used by this package

Save a "dump" of all the parameters that pet_joystick_node uses. Ubuntu Shell

~/ws_ros2/data$ ros2 param dump /joystick_node
  Saving to:  ./joystick_node.yaml

In the following list you can see all the parameters that pet_joystick_node uses. And their default values.
./joystick_node.yaml

/joystick_node:
 ros__parameters:
   adc_i2c_address: '0x48'
   adc_x_channel: 3
   adc_y_channel: 1
   adc_z_channel: 2
   angular_only: 30
   angular_scaling: 0.01
   cycle_timer: 0.1
   cycles_publish: 10
   granularity: 5
   linear_scaling: 0.02
   ros_topic_raw: raw/joystick
   ros_topic_twist: twist/cmd_vel
   ros_topic_twist_stamped: twist_stamped/cmd_vel
   x_polarity: -1
   y_polarity: 1
   z_polarity: -1
   zero_range_max: 5
   zero_range_min: -5

Test the Joystick node

ROS2 Test pet_joystick_node using TurtleSim (indivudal start)

Objective is to control the simulated turtle on screen by using pet_joystick_node.

🤔Most probably have you already the TurtleSim installed as a part of ROS2.
...I will not cover that here!

Initiate ROS2 & launch TurtleSim
Ubuntu Shell #1

~/ws_ros2$ source /opt/ros/galactic/setup.bash
~/ws_ros2$ ros2 run turtlesim turtlesim_node

Show/list used ros-topics that TurtleSim using and look for the "cmd_vel"
Ubuntu Shell #2

~/ws_ros2$ ros2 topic list
	/turtle1/cmd_vel   <- This is the topic name that TurtleSim using.
	/turtle1/color_sensor
	/turtle1/pose
~/ws_ros2$

Set the output ros-topic name for the pet_joystick_node to match the topic-name that TurtleSim using = /turtle1/cmd_vel
One way to do this is set the parameter -p ros_topic_twist:=turtle1/cmd_vel when launching pet_joystick_node
Ubuntu Shell #3

~/ws_ros2$ ros2 run pet_ros2_joystick_pkg pet_joystick_node --ros-args -p ros_topic_twist:=turtle1/cmd_vel
  [INFO] [1645466678.951719930] [joystick_node]: joystick_node has started
  [INFO] [1645466678.954457277] [joystick_node]: - A/D: 0x48, X-chn: 3, Y-chn: 1, Twist-chn: 2
  [INFO] [1645466678.957577325] [joystick_node]: - A/D sampling: 10.0Hz, Topic: turtle1/cmd_vel

ROS2 Launch pet_joystick_node and TurtleSim node via .launch.py file

The same test case as above - TurtleSim Node + Joystick Node.
But this time we launch in one step, via a .launch file.

Ubuntu Shell

~/ws_ros2$ $ ros2 launch pet_ros2_joystick_pkg turtle_joystick.launch.py 
  [INFO] [launch]: All log files can be found below /home/ubuntu/.ros/log/2022-03-06-21-16-49-679386-raspikull8-178148
  [INFO] [launch]: Default logging verbosity is set to INFO
  [INFO] [turtlesim_node-1]: process started with pid [178150]
  [INFO] [pet_joystick_node-2]: process started with pid [178152]

  [turtlesim_node-1] [INFO] [1646597810.933757565] [turtlesim]: Starting turtlesim with node name /turtlesim
  [turtlesim_node-1] [INFO] [1646597810.943631886] [turtlesim]: Spawning turtle [turtle1] at x=[5,544445], y=[5,544445], theta=[0,000000]
  
  [pet_joystick_node-2] [INFO] [1646597813.077173940] [joystick_node]: joystick_node has started
  [pet_joystick_node-2] [INFO] [1646597813.079749163] [joystick_node]: - A/D: 0x48, X-chn: 3, Y-chn: 1, Z-chn: 2
  [pet_joystick_node-2] [INFO] [1646597813.082246831] [joystick_node]: - A/D sampling: 10.0Hz, Topic: turtle1/cmd_vel
~/ws_ros2$

ROS2 Test pet_joystick_node via ROS1_Bridge to TurtleSim on another PC running ROS1

If the target system is based on ROS1 (some legacy robot...). Then this is how you bridge the ROS2 based Joystick_node over to a ROS1 based target system (in this example running TurtleSim under ROS1).